State of California

California Environmental Protection Agency

Air Resources Board

ASSESSMENT OF THE IMPACTS OF TRANSPORTED POLLUTANTS ON OZONE

CONCENTRATIONS IN CALIFORNIA

March 2001

Staff Report: Initial Statement of Reasons

For consideration on

April 26, 2001

Prepared by

Planning and Technical Support Division

Principal Authors

Cynthia Garcia

Steve Gouze

Jeff Wright

Contributing Staff

Rich Hackney

Supervision

Bob Fletcher, Chief, Planning and Technical Support Division

Don McNerny, Chief, Modeling & Meteorology Branch

Debora Popejoy, Manager, Air Quality Analysis Section

John DaMassa, Control Strategy Modeling Section

This report has been reviewed by the staff of the California Air Resources Board and

approved for publication. Approval does not signify that the contents necessarily reflect

the views and policies of the California Environmental Protection Agency or the Air

Resources Board, nor does mention of trade names or commercial products constitute

endorsement or recommendation for use.
TABLE OF CONTENTS

Chapter Page

Summary and Overview................................................................................................. i

I. Background ..............................................................................................................1

A. Introduction ...........................................................................................................1

B. Previous Transport Assessment ...........................................................................1

C. Transport Impact Mitigation ..................................................................................2

D. Public Consultation Process .................................................................................3

E. Definitions and Terminology .................................................................................3

II. Proposed Regulatory Changes...............................................................................5

A. Transport Couples Identification Changes............................................................5

B. Transport Assessment Changes...........................................................................5

III. Transport Couple Assessments .............................................................................7

A. Broader Sacramento Area to Upper Sacramento Valley.......................................7

B. San Francisco Bay Area Air Basin to North Coast Air Basin...............................14

C. San Francisco Bay Area and San Joaquin Valley Air Basins

to South Central Coast Air Basin (San Luis Obispo County) ..............................18

IV. Impact Analysis......................................................................................................25

A. Public Health, Welfare, and Environmental Impacts ...........................................25

B. Economic Impacts...............................................................................................25

C. Alternatives to the Staff’s Proposed Amendments..............................................26

V. Recommendations for Further Research.............................................................27

References ...................................................................................................................29

Appendix Page

A. Text of Health and Safety Code ......................................................................... A-1

B. Public Workshop Notice...................................................................................... B-1

C. Transport Workshop Participants ...................................................................... C-1

D. Glossary................................................................................................................ D-1

E. Proposed Text of Regulation Identifying Areas Which Are Impacted by

Transported Air Pollutants .................................................................................. E-1

F. Technical Support for Assessments .................................................................. F-1

1. Broader Sacramento Area to Upper Sacramento Valley................................... F-2

2. San Francisco Bay Area Air Basin to North Coast Air Basin........................... F-10

3. San Francisco Bay Area and San Joaquin Valley Air Basins

to South Central Coast Air Basin (San Luis Obispo County) .......................... F-15
Summary and Overview i

ASSESSMENT AND MITIGATION OF THE IMPACTS OF TRANSPORTED

POLLUTANTS ON OZONE CONCENTRATIONS IN CALIFORNIA

SUMMARY AND OVERVIEW

The Air Resources Board (ARB or Board) is required1 to 1) identify upwind air basins

or subregions which cause or contribute to violations of the State ozone standard in

downwind air basins or subregions, 2) assess the relative contributions of upwind

emissions to downwind ozone concentrations, and 3) update this assessment at least

every three years. The Board approved the first assessment in August 1990 (ARB

1990). Subsequent updates occurred in August 1993 (ARB 1993) and November 1996

(ARB 1996). This report, which is the third update of the ozone transport couples,

reviews and updates the 1996 assessment.

The ARB staff reviews all the available data in order to determine if there are

impacts in a downwind region from the transport of pollutants from an upwind region. If

transport exists, the staff recommends to the Board that they amend the transport

identification regulation to identify upwind and downwind regions as a transport couple.

As a non-regulatory action, the staff also recommends to the Board that the relative

contribution of the transport be assigned as the classification of “overwhelmed”,

“significant”, or “inconsequential”.

This report proposes to amend two separate regulations: the transport identification

regulation (California Code of Regulations, Title 17, section 70500(c)) and the transport

mitigation regulation (California Code of Regulations, Title 17, section 70600). The

identification regulation lists the upwind and downwind areas, referred to as transport

couples. The transport mitigation regulation requires air basins, which are identified as

upwind areas in the transport identification regulation to adopt best available retrofit

control technology for some existing stationary sources of ozone precursor emissions.

In addition, air basins, which are classified as causing “overwhelming” transport, must

adopt sufficient control measures to attain the State ozone standard in the downwind

areas when conditions are conducive to “overwhelming” transport.

Based on the available data, the ARB staff recommends that two new transport

couples be added to the transport identification regulation:

• The San Francisco Bay Area/North Coast couple; and

• The San Francisco Bay Area/South Central Coast couple.

The ARB staff also recommends the following non-regulatory changes to the ozone

transport assessments:

• A classification of “overwhelming” transport from the San Francisco Bay Area Air

Basin to the northern Sonoma County portion of the North Coast Air Basin;

 

1 Section 39610 of the Health and Safety Code
Summary and Overview ii

• A classification of “significant” transport from the San Francisco Bay Area Air

Basin to the San Luis Obispo County portion of the South Central Coast Air

Basin; and

• A classification of “inconsequential” transport from the Broader Sacramento Area

to the Upper Sacramento Valley.

Table 1 lists all the air basins, which have been identified as transport couples

and the assigned transport classifications. Figure 1 shows where these air basins are

located.

The new assessments, associated with the classification of the transport couples,

requires that the transport mitigation regulation also be amended to reflect the

classification of “overwhelming” transport from the San Francisco Bay Area Air Basin to

the northern Sonoma County portion of the North Coast Air Basin. The other two

assessments do not require amendments to the mitigation regulation, because the San

Joaquin Valley Air Basin and the Broader Sacramento Area were previously identified

as upwind areas and are already subject to the mitigation regulation requirements.

The staff also recommends that future transport analyses take advantage of two

regional field studies which in the aggregate cover many of the ozone non-attainment

areas of the State: the 1997 Southern California Ozone Study and the 2000 Central

California Ozone Study. It is anticipated that the data from these studies will allow for

better three-dimensional characterization of transport and will provide data to examine

transport from a regional, rather than transport couple, perspective.

The ARB 1989, 1990, 1993, and 1996 transport documents on transport couple

identification, assessment, and mitigation are included as part of this report by

reference. (See References )
Summary and Overview iii

Table 1

Summary of Transport Couple Characterizations*

Transport

Transport Couples Characterization**

Previous Proposed

Broader Sacramento Area to Mountain Counties O O

Broader Sacramento Area to San Joaquin Valley S, I S, I

Broader Sacramento Area to San Francisco Bay Area S, I S, I

Broader Sacramento Area to Upper Sacramento Valley O, S O, S, I

California Coastal Waters to South Central Coast S S

Mexico to Salton Sea O, S O, S

Mexico to San Diego O, S, I O, S, I

San Francisco Bay Area to Broader Sacramento Area O, S, I O, S, I

San Francisco Bay Area to Mountain Counties S S

San Francisco Bay Area to North Central Coast O, S O, S

San Francisco Bay Area to North Coast — O

San Francisco Bay Area to San Joaquin Valley O, S, I O, S, I

San Francisco Bay Area to South Central Coast — S

San Joaquin Valley to Broader Sacramento Area S, I S, I

San Joaquin Valley to Great Basin Valleys O O

San Joaquin Valley to Mountain Counties O O

San Joaquin Valley to Mojave Desert O O

San Joaquin Valley to North Central Coast S S

San Joaquin Valley to South Central Coast S, I S, I

South Coast to Mojave Desert O, S O, S

South Coast to Salton Sea O, S O, S

South Coast to San Diego O, S, I O, S, I

South Coast to South Central Coast S, I S, I

South Central Coast to South Coast S, I S, I

* Staff recommended changes shown in bold

** O = Overwhelming, S = Significant, I = Inconsequential
Summary and Overview iv

Fresno

Sonoma

Solano

Alameda

San Mateo

Santa Cruz

Santa Clara

Sonoma

Marin

Contra Costa

San Francisco

Napa

Solano

Merced

Monterey

San Luis Obispo

San Benito

Stanislaus

San Joaquin

Sacramento

Calaveras

Amador

Colusa

Tehama

Mendocino

Lake

Glenn

Del Norte

Humboldt Shasta

Trinity

Siskiyou

Nevada

Placer

Sutter

Yolo

Yuba

El Dorado

Placer

Plumas

Butte

Lassen

Sierra

Modoc

Santa Barbara

Los Angeles

Ventura

Los Angeles

Riverside

San Diego

Orange

Imperial

Riverside

Riverside

San Bernardino

San Bernardino

Alpine

Madera

Kings

Kern

Mariposa

Tuolumne

El Dorado

Placer

Tulare

Kern

Inyo

Mono

4. SOUTH CENTRAL COAST

13. MOUNTAIN COUNTIES

3. NORTH CENTRAL COAST

2. SAN FRANCISCO BAY AREA

9. SAN JOAQUIN VALLEY

7. NORTHEAST PLATEAU 1.NORTH COAST

8. SACRAMENTO VALLEY

14. LAKE COUNTY

11. MOJAVE DESERT

5. SOUTH COAST

6. SAN DIEGO

12. SALTON SEA

15. LAKE TAHOE

10. GREAT BASIN VALLEYS

D

 MILES

0 50 100 150 200 250

Figure 1

California Counties and Air Basins
Background 1

CHAPTER I

Background

A. Introduction

The California Clean Air Act of 1988 (the “Act,” Stats. 1988, Chapter 1568; as

amended by AB 2783, Stats. 1992, Chapter 945) requires each air pollution control and

air quality management district (district) in which a State ambient air quality standard for

ozone, carbon dioxide, sulfur dioxide, or nitrogen dioxide is exceeded to develop a plan

and an emission control program to attain the standard(s). The Act recognizes that

ozone and ozone precursors can be carried by winds over long distances and thereby

contribute to air quality problems outside the district or air basin where they originated.

To address this, the Act requires upwind districts to mitigate the impacts on downwind

areas of pollutants emitted in the upwind districts (see section 39610 of the Health and

Safety Code). The Act directs the Air Resources Board (ARB or Board) to assess the

impacts of such transport and to establish mitigation requirements for upwind districts.

This chapter provides background information related to the assessment of transport

impacts and describes the public consultation process.

B. Previous Transport Assessments

The Act directs the ARB to:

1) Identify downwind areas affected by transported air pollutants and the upwind air

basins or regions that are the sources of the pollutants;

2) Assess the relative contribution of upwind emissions to downwind ozone

concentrations as “overwhelming”, “significant”, “inconsequential”, or some

combination thereof, to the extent permitted by available data (Health and Safety

Code, section 39610(a) and (b)); and

3) Update this analysis at least once every three years (Health and Safety Code,

section 39610(d)).

The assessment of transport couples depends upon the exceedance values at any

given site. All values that exceed the State standard are considered exceedances.

However, the assessment process also considers the expected peak day concentration

(EPDC) threshold. This ozone concentration is a statistically calculated value, which is

not expected to occur more than one time per year. Thus, ozone concentrations greater

than the EPDC are, theoretically, expected to occur less than one time per year on the

average. Those ozone concentrations, which are greater than the State standard, and

less than or equal to the EPDC, are considered violations of the State standard. Those

values which are greater than the EPDC are considered extreme concentrations,

because of the nature of their occurrence. Given that they are extreme concentrations,
Background 2

the staff considers them beyond reasonable regulatory control. Thus, they are not used

in the transport assessment process.

More than one assessment may apply to a transport couple. The assessments rely

on, but are not limited to, meteorological data such as wind speed and direction. As

these parameters vary from day to day, the assessments also vary. Therefore, while

there may be a finding of “inconsequential” transport impacts on one or more violation

days, other days may be assessed as “overwhelming” and/or “significant”. Likewise, an

area that is the upwind air basin on one day may be the downwind air basin on another

day.

In December 1989 (ARB 1989), the ARB adopted a regulation identifying

14 transport couples, each consisting of an upwind area that is the source of

transported ozone or ozone precursors and a downwind receptor area impacted by

those pollutants (Title 17, California Code of Regulations, section 70500). In May 1992,

the ARB approved changes to the transport identification regulation, which redefined the

boundaries of the Upper Sacramento Valley and the Broader Sacramento Area.

In August 1990 (ARB 1990), the ARB approved a qualitative assessment of the

relative contributions of upwind emissions to downwind concentrations. In that

assessment, the relative contribution was qualitatively classified as “overwhelming”,

“significant”, or “inconsequential”. In August 1993 (ARB 1993a), the ARB approved the

first update to the 1990 assessments. In that update, new transport couples were

identified and assessed, the number of areas with mitigation responsibility was

increased, and some previous assessments were updated. In November 1996 (ARB

1996), the ARB approved the second update to the transport assessments. Only a few

minor changes to the assessments took place.

This report represents the third update to the 1990 assessments. The staff

recommends identifying two new couples and modifying the transport characterizations

for one existing couple.

C. Transport Impact Mitigation

Health and Safety Code section 39610(b) directs the ARB to establish mitigation

requirements for upwind districts commensurate with their contributions to the air quality

problems in downwind areas. This was first done with the August 1990 transport

assessment. Three parts to the mitigation requirements applicable to upwind districts

were established:

1) Adopt a “no-net-increase” permitting program for all new or modified stationary

sources;

2) Commit to adopt best available retrofit control technology (BARCT) for some existing

stationary sources of reactive organic gas (ROG) and oxides of nitrogen (NOx)

emissions; and
Background 3

3) Where “overwhelming” transport exists, include sufficient measures in the air quality

plans to ensure expeditious attainment of the State ozone standard in the downwind

district(s).

In March 1993 (ARB 1993b), the ARB approved the deletion of the “no-net-increase”

requirement from the mitigation regulation (section 70600). The effect of this deletion is

that permitting requirements for all districts are those specified in the Act based on the

districts’ nonattainment classification, whether or nor the district is a source of

transported pollutants. (See Health and Safety Code section 40918 et. seq. found in

Appendix A) The remaining two mitigation requirements were not changed. The staff is

not proposing to change the mitigation requirements of upwind areas at this time. The

staff only recommends amendments that redefine which areas are subject to the

mitigation requirements.

D. Public Consultation Process

ARB staff participated in several transport working groups to share data, analyses,

and recommendations for the proposed assessments. In addition, the staff conducted a

public consultation workshop on November 4, 1999. A copy of the workshop notice is

provided in Appendix B, and the list of workshop participants is shown in Appendix C.

E. Definitions and Terminology

Below are some terms used frequently in this report. See Appendix D for a glossary

of many other commonly used terms:

Inconsequential – ozone transport classification describing a condition when upwind

emissions were not transported or did not appear to contribute significantly to a

violation of the State ozone standard in the downwind area. A violation not impacted

by transported emissions is considered local and results when the wind flow patterns

and atmospheric conditions do not strongly suggest responsibility from an upwind

area. The responsibility of “inconsequential” transport lies with the downwind area.

Overwhelmed – ozone transport classification describing a condition when the

emissions from the upwind area independently result in a violation of the State

ozone standard in the downwind area on any given day. Significant emission

sources in the downwind area were not in the pathway of the air parcel that was

transported from the upwind area. The responsibility for a violation caused by

“overwhelming” transport lies with the upwind area.

Significant – ozone transport classification describing a condition in which the

emissions from the upwind area contributed measurably to a violation of the State

ozone standard in the downwind area on any given day, but did not “overwhelm” the

area. A violation is considered caused by “significant” transport if the emissions

from sources within the downwind area combine with the transported parcel carrying

ozone or ozone precursors from the upwind area. A violation classified as
Background 4

“significant” is considered shared, with responsibility lying with both the upwind and

downwind areas.
Proposed Regulatory Changes 5

CHAPTER II

Proposed Regulatory Changes*

A. Transport Couples Identification Changes

The staff proposes to identify two new transport couples. One new couple is the

San Francisco Bay Area Air Basin to the North Coast Air Basin, based on assessment

of impacts to the Sonoma County portion of the North Coast Air Basin. The staff

recommends this couple be incorporated into the transport identification regulation

(California Code of Regulations, Title 17, Subchapter 1.5, Article 5, section 70500(c)).

See Appendix E for the text of the proposed regulation.

The other new couple is the San Francisco Bay Area Air Basin to the South Central

Coast Air Basin, based on the assessment of impacts to San Luis Obispo County. The

staff recommends that this couple be incorporated into the transport identification

regulation (California Code of Regulations, Title 17, Subchapter 1.5, Article 5, section

70500(c)). See Appendix E for the text of the proposed regulation.

B. Transport Assessment Changes

The staff recommends the assessment of transport impacts from the San Francisco

Bay Area Air Basin to the North Coast Air Basin be classified as “overwhelming”. The

new assessment associated with this “overwhelming” classification, requires the

transport mitigation regulation (California Code of Regulations, Title 17, Subchapter 1.5,

Article 6, section 70600(b)) to be amended to reflect the classification of “overwhelming”

transport from the San Francisco Bay Air Basin to the Sonoma County portion of the

North Coast Air Basin. See Appendix E for text of the regulation.

The transport mitigation regulation requires air basins, which are identified as

upwind areas in the transport identification regulation, to adopt best available retrofit

control technology for some existing stationary sources of ozone precursor emissions.

In addition, air basins, which are classified as causing “overwhelming” transport, must

adopt sufficient control measures to attain the State ozone standard in the downwind

areas when conditions are conducive to “overwhelming” transport.

 

*

In addition to the changes identified, the staff also assessed transport for two exisitng transport

couples. The staff found that on some days, there is “inconsequential” transport from the

Broader Sacramento Area to the Upper Sacramento Valley, and that on some days threre is

“significant” transport from the SanJoaquin Valley Air Basin to San Luis Obispo County in the

South Central Coast Air Basin. However, thes findings will not result in any amendments to the

transport regulations, because the Broader Sacramento Area/Upper Sacramento Valley and the

San Joaquin Valley Air Basin/South Central Coast Air Basin were previously identified as

transport couples.
Proposed Regulatory Changes 6

Chapter III provides the details of the staff’s analyses to support the proposed

changes to both the transport couple identifications and assessments.
Transport Couple Assessments 7

CHAPTER III

Transport Couple Assessments

A. Broader Sacramento Area to Upper Sacramento Valley

1. Recommendation

The Air Resources Board (the Board or ARB) staff recommends, based on the

recent analyses, to re-instate the classification of “inconsequential” to the Upper

Sacramento Valley (USV). In addition to the 1996 transport assessment of “significant”

and “overwhelmed”, the transport of pollutants from the Broader Sacramento Area

(BSA) was found to be “inconsequential” as measured at the monitoring site at Redding

in Shasta County. “Inconsequential” transport means that little or no transport impacted

the monitor and that the exceedance was due to local emissions. This assessment

does not require a regulatory change because this transport couple has been identified

previously, and this work illustrates that emissions in the Upper Sacramento Valley can,

on occasion, cause exceedances of the State ozone standard without a transport

component.

2. Background

a. Previous Assessments

Based on previous assessments, the ARB concluded that historically, the Upper

Sacramento Valley (USV) was impacted by “overwhelming”, “significant”, and

“inconsequential” transport from the Broader Sacramento Area (BSA). Based on the

1993 and 1996 assessments, transport from the BSA was found to be “overwhelming”

at the following air monitoring sites:

Chico (Butte County) Arbuckle (Colusa County)

Willows (Glenn County) Redding (Shasta County)

Yuba City (Sutter County) Red Bluff (Tehama County)

Based on the 1990 and 1996 assessments, transport was found to be “significant” at

the following air monitoring sites:

Chico (Butte County) Colusa and Arbuckle (Colusa County)

Willows (Glenn County) Redding and Anderson (Shasta County)

Yuba City (Sutter County) Red Bluff (Tehama County).

Based on the 1990 assessment, transport was found to be “inconsequential” at:

Redding and Anderson (Shasta County).
Transport Couple Assessments 8

In the 1996 assessment, it was found that none of the sites had “inconsequential”

transport during the period 1994 through 1996 and therefore, the “inconsequential”

transport assessment was removed.

b. Transport Working Group

The ARB staff and the Shasta County district staff formed the Shasta County

Transport Working Group. This group shared data, analyses, suggestions, and

pertinent recommendations. Group members met once in June 1999 and also

discussed the analyses during several phone calls. Since the number of State ozone

exceedance days in Shasta County increased significantly during 1996-98 compared to

the previous three year period and because both “significant” and “overwhelming”

transport episodes have already been well documented, the Working Group focused on

analyzing for an “inconsequential” transport episode.

3. Geographical Features

A detailed description of the geography of the Sacramento Valley can be found on

page VII.7 of the 1993 transport "Assessment and Mitigation of the Impacts of

Transported Pollutants on Ozone Concentrations in California." The important features

related to this analysis are that Shasta County is located at the northern end of the

Sacramento Valley. Shasta County is surrounded by mountains on three sides,

providing a bowl, which allows, under some meteorological conditions, for emissions

and pollutants to accumulate and/or recirculate. Figure 2 is a map of the Sacramento

Valley, which shows the major geographic features.

4. Emissions

Shasta County is the second highest emitter of NOx and ROG within the Sacramento

Valley Air Basin (SVAB), with Sacramento County being the highest. The highest

emitting facilities of NOx in the SVAB are located in Shasta County. The highest emitter

of NOx within the SVAB is Calaveras Cement Company with 559 tons/year located in

the city of Redding. Three other high emitting facilities of NOx within the SVAB are

located in the city of Anderson: Simpson Paper Company with 377 tons/year,

Wheelabrator Energy with 364 tons/year, and Wheelabrator Lassen with 227 tons/year.

In addition, the city of Burney has a high emitting facility for NOx, the PG&E plant

producing 220 tons/year.

5. Population

Shasta County has the second highest population in the USV, second to Butte

County. Shasta County's immediate neighboring counties to the south are Tehama

and Butte County. Together these three counties constitute approximately

70 percent of the USV population with a total 1998 population of 418,100. The

average growth for these three counties between 1990-1998 was 10 percent.
Transport Couple Assessments 9

Figure 2

Geographic Features of the Sacramento Valley
Transport Couple Assessments 10

6. Analysis

Shasta County had its worst year on record in 1998 with 40 State ozone

exceedances. In addition, the ozone trend for Shasta County has remained flat

between 1980 through 1998, whereas the ozone trend for this same period in

Sacramento County shows a downward trend. This prompted the ARB staff to reevaluate transport to determine if Shasta County was affected by “inconsequential”

transport resulting in local exceedance days.

The ARB staff screened 1997 and 1998 ozone exceedances (1996 data have been

independently evaluated by Sonoma Technology Inc.) and identified three possible local

days. These proposed local exceedances occurred on August 4, 1997,

August 19, 1998, and September 24, 1998.

Air quality and meteorological data were evaluated for evidence of transport impacts.

Both spatial and temporal analyses were done to establish the extent of the

exceedances and the time of day that they occurred. Diurnal profiles, which are the

ozone concentrations that occurred throughout the day, were used to understand the

behavior of the ozone concentrations. Maximum concentrations which occur in the

early morning may indicate the possibility of ozone trapped aloft which fumigates to the

surface as the surface temperatures increase. The assessment of transport impacts

requires a three dimensional analysis. Therefore, air quality and meteorological data for

different altitudes is helpful in understanding the possibility of transport of air pollutants

aloft. The monitors located on top of the Sutter Buttes and Tuscan Buttes in the

Sacramento Valley area represent the air quality aloft. Sutter Buttes is located at

2,132 feet in Sutter County and Tuscan Buttes is at 1,868 feet in Tehama County. (See

Appendix F for more detailed technical description of the analyses.)

a. Analysis of the August 4, 1997 Exceedance

Summary

The staff found that the exceedance on this day was caused by local emissions and

not transported pollutants from the Broader Sacramento Area (BSA). Both surface and

aloft wind directions and speeds were not conducive for transport from the BSA to

Shasta County. In addition, the temporal and spatial characteristics of the exceedance

are consistent with a locally generated ozone exceedance.

Air Quality

Shasta County exceeded the State ozone standard on August 4, 1997, with a daily

maximum concentration of 0.097 ppm. The analysis included data for the period of

August 2, 1997, through August 4, 1997. The air quality for the entire Sacramento

Valley Air Basin (SVAB) was reviewed for spatial and temporal relationships.
Transport Couple Assessments 11

The exceedance in Shasta County occurred near the noon hour, indicating

contribution from locally generated emissions. Only one monitor in the BSA had an

exceedance during this period, which occurred at noon on the same day as in Shasta

County. In addition, the concentrations at Tuscan and Sutter Buttes were low which

indicate no significant contribution to Shasta County exceedance from BSA transport

aloft.

Meteorology

The surface winds were affected by a high pressure system located at the most

northern extent of the Sacramento Valley (Shasta County), and a low pressure system

located over most of the remainder of the Sacramento Valley. (High-pressure systems

are conducive for ozone formation, whereas, low-pressure systems are conducive for

the dispersion, and dilution of emissions and pollutant concentrations.) For most of this

period, there were weak northerly surface winds in the northern portion of the USV.

Moreover, an early morning calm was observed for each of these three days, allowing

local emissions to build. These meteorological conditions are not conducive for surface

transport from the BSA to Shasta County.

The aloft winds were also affected by these two pressure systems. The day prior to

the exceedance, the wind direction at Sutter Buttes for the evening was from the south

and the wind speed was very low (1 mile per hour). In addition, the wind direction at the

Tuscan Butte site for the morning hours was from the north and the wind speed was 4

miles per hour. The aloft wind directions and speeds are not conducive for the transport

of significant pollutants from the BSA to Shasta County.

b. Analysis of the August 19, 1998 Exceedance

Summary

The staff found that the exceedance on this day was caused by local emissions, and

not by transported pollutants from the BSA. Both surface and aloft wind directions and

speeds were not conducive for transport from the BSA to Shasta County. In addition,

the temporal and spatial characteristics of the exceedance are consistent with a locally

generated ozone exceedance.

Air Quality

Shasta County exceeded the State ozone standard on August 19, 1998 with a daily

maximum concentration of 0.100 ppm. The analysis included data for the period of

August 17, 1998 through August 19, 1998. Air quality for the entire SVAB was reviewed

for spatial and temporal relationships.

For the duration of this period, Shasta County was the only area within the SVAB

that exceeded the State ozone standard. The exceedance occurred near the noon hour

indicating contribution from locally generated emissions. In addition, the aloft
Transport Couple Assessments 12

concentrations at Tuscan and Sutter Buttes were low, indicating that transport aloft from

the BSA did not contribute to the Shasta County exceedance.

Meteorology

The surface winds for this three day period were affected by a shifting surface high

pressure system located near or around the most northern extent of the Sacramento

Valley (Shasta County), and a surface low pressure system located over most of the

remainder of the Sacramento Valley. On each of the three days, an early morning calm

or northerly wind was observed, allowing local emissions to build or potentially to

recirculate.

The aloft winds were also affected by these two pressure systems. The day prior to

the exceedance, the wind direction at Sutter Buttes was from the south and the wind

speed was very low (3 miles per hour). The wind direction at the Tuscan Buttes site

was from the north and the wind speed was 5 miles per hour. These aloft wind

directions and speeds are not conducive for the transport of pollutants from the BSA to

Shasta County.

c. Analysis of the September 24, 1998 Exceedance

Summary

The staff found that the exceedance on this day was caused by local emissions, and

not by transported pollutants from the BSA. Both surface and aloft wind directions and

speeds were not conducive for transport from the BSA to Shasta County. In addition,

the temporal and spatial characteristics of the exceedance are consistent with a locally

generated ozone exceedance.

Air Quality

Shasta County exceeded the State ozone standard on September 24, 1998, with a

daily maximum concentration of 0.100 ppm. The analysis included data for the period

of September 21, 1998, through September 24, 1998. The air quality for the entire

SVAB was reviewed for spatial and temporal relationships.

For the duration of this period, Shasta County was the only area within the SVAB

that exceeded the State ozone standard. The exceedance occurred mid-afternoon,

indicating contribution from locally generated emissions from within Shasta County,

where some emissions from adjacent counties within the USV could have contributed.

The aloft concentrations at Tuscan and Sutter Buttes were low. The maximum

concentrations at the monitors on the Tuscan and Sutter Buttes occurred at the same

time as the maximum concentration at Redding. On the evening prior to the

exceedance day, the ozone concentrations at the Sutter Buttes site were also low.

During the early morning of the exceedance day, the ozone concentrations at the
Transport Couple Assessments 13

Tuscan Buttes site were also low. This indicates that the ozone aloft did not appear to

contribute significantly to the exceedance.

Meteorology

During this period, Shasta County had higher ambient temperatures than in

Sacramento County. This indicates that Shasta County's temperature was more

conducive for ozone formation.

On September 21, 1998, a northerly wind was prevalent for most of the day, which

allowed for the clean day in the SVAB. The period from September 22-24 had very

similar meteorological conditions. During all three days, an evening and early morning

calm was observed, allowing local emissions to build.

During the last three days of this period, the highest ozone concentration occurred

about the same time as the daily temperature peaked. The temperature peaked at 27°C

in Redding, and peaked at 24.9°C in Folsom. The wind trajectory model runs were

consistent with the above analysis, indicating that the emissions, which impacted the

Redding monitor most likely, originated in Tehama and Shasta Counties.

7. Conclusions

The ARB staff determined that the ozone exceedances on August 4, 1997,

August 19, 1998, and September 24, 1998, at Redding in Shasta County had little or no

impact from transport of upwind emissions from the Broader Sacramento Area. Based

on these recent analyses, the staff recommends that the USV transport classification

include that of “inconsequential” transport in addition to that of the 1996 assessment of

“significant” and “overwhelming” impacts. The staff’s findings indicate that Shasta

County, as well as the neighboring counties, has a responsibility to reduce emissions to

attain the State ozone standard in the USV.
Transport Couple Assessments 14

B. San Francisco Bay Area Air Basin to North Coast Air Basin

1. Recommendation

The staff’s analysis indicates that transport from the San Francisco Bay Area Air

Basin (SFBAAB) caused exceedances of the State ozone standard in the Sonoma

County portion of the North Coast Air Basin (NCAB). This conclusion is based on

screening all nine exceedance days in Healdsburg (the only ozone monitoring site

located in the Sonoma County portion of the NCAB) during 1996-98 and analyzing all

five exceedance days that were not excluded as extreme concentrations. There are no

indications that the Sonoma County portion of the NCAB (northern Sonoma County) is

capable of exceeding the State ambient air quality standard for ozone without transport

from an upwind area. The September 24, 1997 exceedance is presented as an

example of an exceedance due to “overwhelming” transport.

The staff recommends that the Board classify the transport of ozone (and its

precursors) from the SFBAAB to the NCAB as “overwhelming”. The staff also

recommends that the air quality attainment plan of the Bay Area Air Quality

Management District include sufficient measures to attain the State ozone standard

within northern Sonoma County.

2. Background

In 1999, the Sonoma County portion of the NCAB (northern Sonoma County) was

designated nonattainment for the State ozone standard for the first time. As a newly

designated nonattainment area with few stationary sources and low vehicle volumes,

the staff believed that a transport assessment was necessary.

3. Geographical Features

Figure 3 shows the geographic setting of this transport couple. The SFBAAB

comprises all or parts of nine counties: Alameda, Contra Costa, Marin, Napa,

San Francisco, San Mateo, Santa Clara, the western portion of Solano, and the

southern portion of Sonoma County. However, due to their spatial relationship with

northern Sonoma County and the predominant windflow pattern throughout the

SFBAAB, Marin, Napa, and the southern portion of Sonoma County have the greatest

potential to impact air quality in northern Sonoma County. The NCAB is comprised of

all or parts of five counties: Del Norte, Humboldt, Mendocino, Trinity, and northern

Sonoma County. However, due to the rugged topography of much of the NCAB, the

only emissions in the NCAB that are likely to contribute to exceedances in Healdsburg

are those occurring in northern Sonoma County.

Healdsburg is located at the north end of the Santa Rosa Plain where it narrows

from approximately 15 miles wide near Santa Rosa to about five miles wide at

Healdsburg. The Santa Rosa Plain extends roughly in a north-south direction.
Transport Couple Assessments 15

Therefore, the predominant onshore flow observed during the summer and fall months

result in the frequent southerly winds observed throughout the Santa Rosa Plain.

4. Emissions

The staff used the 1996 emission inventory data for statewide, air basin, and county

totals. While such emission totals provide only general information, they are useful for

determining the relative difference in emissions between various areas. Emissions in

the SFBAAB for both NOx and ROG are roughly ten times greater than that of the

NCAB. Emissions in the Sonoma County portion of the SFBAAB are about 3-4 times

greater than the Sonoma County portion of the NCAB. Emissions from the northern

counties of the SFBAAB (southern Sonoma, Marin, and Napa Counties) are about

7 times greater than in northern Sonoma County. Additionally, there are no major

stationary sources of ROG or NOx between the basin boundary and the Healdsburg

monitor.

5. Population

Healdsburg, with a mere population of 10,000, is located just five miles north of the

basin boundary separating the SFBAAB and the NCAB. In addition, Healdsburg is only

approximately 15 miles north of Santa Rosa, a fast growing metropolitan area with an

estimated population of 140,000. Windsor, an area of new development, is a town

10 miles north of Santa Rosa and only two miles south of the basin boundary.

Windsor’s population is estimated to be 20,000. The population of Sonoma County

south of the basin boundary (the SFBAAB portion) is approximately seven times greater

than its northern counterpart (the NCAB portion). In addition, the combined population

of the SFBAAB portion of Sonoma County, Marin County, and Napa County is more

than 13 times greater than the population of northern Sonoma County. Finally, the

population of the entire SFBAAB is approximately 20 times greater than the NCAB.

6. Analysis of the September 24, 1997 Exceedance

Summary

There were nine exceedance days measured in Healdsburg during 1996-98. Four of

these days can be excluded as extreme concentrations. (An extreme concentration is a

concentration that is statistically expected to recur less frequently than once every

year.) Exceedances identified as extreme concentrations are not considered violations

and were not included in this transport assessment because attainment designations

are based only on violations. Those days not considered extreme concentration events

are violations days. The staff analyzed all five violation days and found all five violation

days to be “overwhelmed” by transport of ozone and/or ozone precursor emissions from

the SFBAAB. The September 24, 1997 exceedance is presented as an example of an

exceedance due to “overwhelming” transport. (See Appendix F for more detailed

technical description of the analyses.)
Transport Couple Assessments 16

Figure 3

Geographic features of Sonoma County and Surroundings
Transport Couple Assessments 17

Air Quality

The analysis included data for the period of September 22, 1997 through

September 24, 1997. Ozone maximums on September 22 were very low (near

background levels) except at Healdsburg which recorded 0.07 parts per million (ppm).

Ozone concentrations in Healdsburg and southward increased on September 23. The

upward trend continued on September 24, 1997, when Healdsburg exceeded the State

ozone standard with a 0.10 ppm for four consecutive hours.

On September 24, high ozone values were observed from San Rafael to

Healdsburg. The exceedance at Healdsburg lasted until early evening, which is an

indication that the ozone concentrations may be impacted by transport.

Meteorology

Surface wind observations along the transport route from the SFBAAB to

Healdsburg predominantly measured wind coming from a southerly direction from

September 22 up until the mid-afternoon exceedance on September 24. Sites

recording south winds include Petaluma, Santa Rosa, Windsor, and Healdsburg.

Surface wind trajectories were simulated for this episode. The trajectories

consistently point toward the Santa Rosa area as the upwind area contributing to

Healdsburg’s ozone concentrations. It is also possible that carry-over emissions from

areas south of Santa Rosa may have contributed to Healdsburg’s ozone exceedances.

The staff also examined upper-level winds for indications of transport. The upper air

meteorological sites that were analyzed include Oakland, Reno, Bodega Bay, and

Sacramento. In addition, data from surface sites located on mountain peaks were used

to approximate upper level winds at their corresponding elevations.

For the hours leading up the exceedance in Healdsburg on September 24, 1997,

winds aloft were generally southeasterly and easterly. Therefore, the immediate upwind

region is the SFBAAB.

7. Conclusion

The ARB staff concluded that all five violation days in northern Sonoma County were

caused by “overwhelming” transport from the SFBAAB based on the evaluation of the

topography, airflows, temporal and spatial extent of the ozone concentrations, and a

comparison of the emissions and populations. The staff’s findings indicate that the

San Francisco Bay Area Air Basin is responsible for the attainment of the State ozone

standard in the Sonoma County portion of the North Coast Air Basin. Since local

emissions in northern Sonoma County do not contribute significantly to the

exceedances, the Northern Sonoma County Air Pollution Control District will not need to

comply with the planning requirements of the California Clean Air Act.
Transport Couple Assessments 18

C. San Francisco Bay Area and San Joaquin Valley Air Basins to South Central

Coast Air Basin (San Luis Obispo County)

1. Recommendations

The staff recommends that the Board continue to classify the transport from the

San Joaquin Valley Air Basin to the South Central Coast as “significant” and

“inconsequential” as was found in the 1993 transport assessment report. The staff also

recommends that “significant” transport from the San Francisco Bay Area Air Basin and

the San Joaquin Valley Air Basin, collectively, can “overwhelm” the South Central Coast

Air Basin (San Luis Obispo County portion only). In addition, the staff found that

emissions from the San Francisco Bay and San Joaquin Valley Air Basins combine with

local emissions to cause exceedances in San Luis Obispo County. Therefore, the staff

recommends that the Board identify the San Francisco Bay Area Air Basin to South

Central Coast Air Basin as a new transport couple.

2. Background

A transport assessment was conducted for San Luis Obispo County (the County) at

the request of the San Luis Obispo County Air Pollution Control District (the District).

This request was due to an unusually high number of State 1-hour ozone exceedances

in 1998. 1998 was the worst year on record, with 25 ozone exceedance days.

a. Previous Assessments

In 1993, the Board concluded that the County was impacted by “significant” and

“inconsequential” ozone transport from the San Joaquin Valley Air Basin (SJVAB). The

staff found that ozone exceedances in the County could be the result of combined

emissions from within the County and emissions transported from the SJVAB via winds

aloft. An analysis performed by the District for an exceedance in 1989 indicated that

there was no “significant” transport from regions outside the County for that

exceedance. Thus, the analysis indicates “inconsequential” transport from SJVAB.

b. Transport Working Group

In 1993, the Board directed the ARB staff to work more directly with the districts’

staffs to assess transport. A result of this direction was the formation of the San Luis

Obispo County Transport Working Group. This group comprised the staff from the Bay

Area Air Quality Management District, Monterey Bay Unified Air Pollution Control

District, San Joaquin Valley Unified Air Pollution Control District, the District, and the

ARB. The purpose of the working group was to assess the impact of transport on days

exceeding the State ozone standard in the County during 1996-1998. The working

group met three times during 1999 and once in 2000.
Transport Couple Assessments 19

3. Geographical Features

Figure 4 shows the locations of important geographical features referenced in this

discussion. The County is located in the northern section of the South Central Coast Air

Basin. Monterey County borders it to the north, Santa Barbara County to the south, the

Pacific Ocean to the west, and the San Joaquin Valley to the east.

4. Emissions

Comparisons of the 1996 emission inventories for ozone precursors were conducted

for the County, neighboring counties, and air basins. While such emission totals

provide only general information, they are useful for determining the relative difference

in emissions between various areas. There is a wide disparity between emission

inventories in the County and other areas. The NOx emissions in North Central Coast

Air Basin (NCCAB), southern San Francisco Bay Area Air Basin (SFBAAB), San

Joaquin Valley Air Basin, and Monterey plus San Benito Counties are nearly 2 to 15

times the emissions generated in the County. The ROG emissions in North Central

Coast Air Basin, southern San Francisco Bay Area Air Basin, San Joaquin Valley Air

Basin, and Monterey plus San Benito Counties are nearly 2 to 17 times the emissions

generated in the County.

The combined emissions of central and southern San Joaquin Valley Air Basin are

4-6 times the NOx and 4-7 times the ROG inventories of the County. These emission

inventory relationships indicate that emissions in adjacent areas, under appropriate

meteorological conditions, have the potential to significantly and overwhelmingly impact

the County.

5. Population

Population growth for the entire county was 4.6% between 1990 and 1995. The

population rose from 217,162 to 227,225 during this period. The greatest increase in

population occurred in the upper Salinas Valley area. However, this growth represents

less than 4,000 residents. Population growth in the surrounding air basins has

increased from 1990 to 1995. The greatest population growth was within the San

Joaquin Valley Air Basin.

6. Analysis

All 1996 through 1998 ozone exceedance days were first screened to determine

which were violations of the State Ambient Air Quality Standard using the criteria for

extreme concentrations. The working group looked at all the violation days with the

focus on analyzing examples of “overwhelming”, “significant”, and “inconsequential”

ozone transport. The working group identified an ozone episode that represented each

of the
Transport Couple Assessments 20

Figure 4

Geographic Features of Central California
Transport Couple Assessments 21

three kinds of transport impacts. The working group determined that ozone from both

the SJVAB and SFBAAB “overwhelmingly” impacted Paso Robles and “significantly”

impacted Atascadero on August 28, 1998. Paso Robles and Atascadero were

“significantly” impacted by transported ozone from the SJVAB on May 11, 1996. In

addition, the working group determined that emissions solely from within the County

caused the ozone exceedance at Atascadero on September 1, 1996. (See Appendix F

for more detailed technical description of the analyses.)

a. “Overwhelming” and “Significant” Transport Impact – August 28, 1998

Summary

This analysis suggests that significant emissions from the SFBAAB joined significant

emissions from the SJVAB to collectively “overwhelm” Paso Robles on August 28. In

addition, this analysis suggests that these emissions impacting Paso Robles continued

southward to impact Atascadero. However, the combination of these transported

emissions along with sufficient local emissions resulted in a “significant” impact at

Atascadero.

Air Quality

The analysis included data for the period of August 26 through August 28, 1998.

The ozone air quality on August 26 was good except in the isolated areas in central and

southern SJVAB. On August 27, ozone maximum concentrations increased at Paso

Robles and Atascadero, as well as aloft at Black Mountain (the District’s special study

air monitoring site at 3600 feet) and the adjacent air basins. The ozone concentrations

continued to increase on August 28, when both Paso Robles and Atascadero exceeded

the State ozone standard. The State ozone standard was also exceeded in the

adjacent air basins including SFBAAB at Livermore, and throughout central and

southern SJVAB. The NCCAB ozone concentrations remained low except for the inland

site at Hollister and the higher elevation site at Pinnacles National Monument

(1100 feet).

The time of peak ozone concentrations on August 28 occurred in the early evening

in the County, mid to late afternoon at Hollister and Pinnacles National Monument, and

late afternoon in the Santa Clara Valley. These late peak times indicate impacts from

transported emissions. The progression of the hour of peak ozone concentration

extends southward from the southern SFBAAB to Pinnacles then Paso Robles and

Atascadero. This progression suggests that transported emissions from the SFBAAB

impacted the northern County.

Meteorology

On August 27, strong high pressure aloft covered the southwestern United States

and was highest over central California. As the high pressure increased from August 27

to 28, ozone exceedances became more widespread across central California.
Transport Couple Assessments 22

Central California surface winds during August 27 and 28 were generally northwest

to north. Surface back trajectories indicated that the San Jose area was the upwind

area contributing to the ozone concentrations in the County. Data from Fort Ord show

winds aloft were from the north to northeast. Winds at Black Mountain were eastnortheast.

Surface temperatures in southern Monterey County to central San Luis Obispo

County were the highest throughout central California on August 28. Peak

temperatures at Paso Robles reached 104 degrees Fahrenheit on August 28. Peak

temperatures in the SJVAB reached 99 and 97 degrees on August 28 at Fresno and

Bakersfield, respectively. The high surface temperatures on August 28 resulted in deep

vertical mixing. This deep vertical mixing could have served as a mechanism to further

draw air into the area where the exceedances occurred in the County, thus enhancing

transport and vertical interchange.

b. “Significant” Transport Impact – May 11, 1996

Summary

This analysis suggests that significant surface emissions from within the San Luis

Obispo County joined significant aloft emissions from the SJVAB to cause ozone

exceedances in the County on May 11, 1996.

Air Quality

The analysis included data for the period of May 9 through May 11, 1996. Maximum

ozone concentrations on May 9 were low throughout central California. Ozone

concentrations increased at Paso Robles and Atascadero, as well as in the adjacent air

basins on May 10. Concentrations continued to increase on May 11, when both Paso

Robles and Atascadero exceeded the State ozone standard with 0.097 ppm. In

addition, ozone concentrations exceeding the State ozone standard occurred in all the

adjacent air basins. The time of peak ozone concentrations on May 11 occurred in the

early afternoon in the northern County, mid to late afternoon at Hollister and Pinnacles

National Monument, and late afternoon in the Santa Clara Valley. The lack of a

progression of the hours of the peak ozone concentrations from the SFBAAB to Paso

Robles, does not suggest a transport connection.

The timing and distribution of the daily maximum ozone concentration on May 10

suggests that the Hanford exceedance was primarily the result of surface emissions

from the Fresno urban plume and not the SFBAAB. The elevated daily maximum ozone

concentrations at Tracy and Crows Landing on May 11 indicate that some SFBAAB

emissions impacted northern SJVAB, although, these concentrations are below the

State 1-hour ozone standard. In addition, the timing of the daily maximum ozone

concentration at these two northern SJVAB sites is similar to Paso Robles and

Atascadero, not considerably prior. Therefore, it’s doubtful that significant SFBAAB
Transport Couple Assessments 23

emissions via the San Joaquin Valley contributed to the May 11 ozone exceedances at

Paso Robles and Atascadero.

Meteorology

On May 10 high pressure aloft was centered along the western U. S. coast. The

center of this high pressure moved eastward into the Great Basin by the late afternoon

of May 11, becoming stronger as it moved over California. As the high pressure over

California increased from May 10 to 11, ozone exceedances became more widespread

across central California.

This increase in high pressure over California brought light to moderate winds from

the north to northeast in the northern County on May 10-11. Surface back trajectories

indicated that the surface northerly flow was very weak, and therefore, not consistent

with transport from the SFBAAB. The winds aloft on May 11 were generally offshore at

Vandenberg AFB, Fort Ord, Oakland, and Fresno.

Surface temperatures in Paso Robles, Atascadero, and the San Joaquin Valley were

high on May 11. Peak temperatures at Paso Robles and Atascadero reached 95 and

91 degrees Fahrenheit. Peak temperatures at Fresno and Bakersfield were 90 and

88 degrees Fahrenheit, respectively. The high surface temperatures resulted in deep

vertical mixing on May 11 over the County and central and southern SJVAB. This deep

vertical mixing could have served as a mechanism to further draw air into the area

where the exceedances occurred in the northern County, thus enhancing transport and

vertical interchange.

c. “Inconsequential” Transport Impact – September 1, 1996

Summary

This analysis suggests that emissions predominantly within the County resulted in a

1-hour exceedance of the State ozone standard at Atascadero on September 1. As a

result, Atascadero was impacted by “inconsequential” transport on September 1, 1996.

This indicates San Luis Obispo County will need to reduce the emissions within the

County to reach attainment of the State ozone standard.

Air Quality

The analysis included data for the period of August 31 through September 1, 1996.

Maximum ozone concentrations on August 31 were low in the County, moderate in the

NCCAB, and exceeded the state ozone standard in the southern SFBAAB and in the

SJVAB. By September 1 ozone concentrations increased in the northern County, but

decreased in the adjacent air basins.

Elevated concentrations of oxides of nitrogen were measured at Atascadero during

the morning and evening hours of August 31. The local emissions of oxides of nitrogen
Transport Couple Assessments 24

were magnified by the increased Labor Day traffic on U. S. Highway 101. Elevated

concentrations of oxides of nitrogen continued overnight and into the morning hours of

September 1.

Meteorology

On August 31 high pressure was centered over the California’s central coast and

desert interior, causing the buildup of ozone concentrations in the central and southern

portions of California. However, by September 1 lower pressure aloft resulted in

decreased ozone concentrations over portions of central and southern California except

for the northern County.

The nighttime and morning surface winds at Atascadero were calm on August 31

and September 1. Afternoon west-southwest seabreeze winds were light on August 31

and September 1. The winds aloft at Vandenberg AFB, Oakland, and Fresno were

generally onshore both on August 31 and September 1. The surface backward

trajectory from Atascadero indicated that air arriving in Atascadero at the time of the

peak ozone concentration had originated off the coast earlier in the day.

7. Conclusions

The staff concluded that on at least one day during 1996-1998, emissions within San

Luis Obispo County were solely the cause of an exceedance of the State ozone

standard in the County. On at least one other day, significant emissions from within the

County combined with transported emissions from the SJVAB to cause an exceedance.

On another day, the staff found that an exceedance was due to significant emissions

from the SFBAAB and the SJVAB that collectively “overwhelmed” Paso Robles. In

addition, on this day, significant emissions from the SFBAAB, SJVAB, and from within

the County were the cause of an exceedance.

The staff's findings indicate that San Luis Obispo County will need emission

reductions from both the San Francisco Bay Area and the San Joaquin Valley to reach

attainment of the State ozone standard. In addition, the findings indicate that there is a

shared responsibility of San Francisco Bay Area, San Luis Obispo, and San Joaquin

Valley to reduce emissions. Finally, the findings indicate San Luis Obispo will need to

reduce the emissions within the county to reach attainment of the State ozone standard.
Impact analysis 25

CHAPTER IV

Impact Analysis

A. Public Health, Welfare, and Environmental Impacts

The proposed amendments are not expected to affect any existing upwind mitigation

requirements since the staff is not identifying any new upwind areas. Therefore, the

adoption of the proposed amendments is not expected to result in any adverse impacts

on public health and welfare.

B. Economic Impacts

The proposed amendments do not change any of the requirements in place

pursuant to the current version of the regulation. Therefore, these regulations have no

direct economic impact, and the following general determinations are appropriate:

The Executive Officer has determined that adoption of the proposed amendment will

not create costs or savings, as defined in Government Code section 11346.5(a)(6), to

any State agency or in federal funding to the State, costs or mandate to any local

agency or school district whether or not reimbursable by the State pursuant to Part 7

(commencing with section 17500), Division 4, Title 2 of the Government Code, or other

nondiscretionary savings to local agencies.

The Executive Officer also has determined, in accordance with Government Code

section 11346.5(a)(8), that adoption of the proposed amendment will not have a

significant adverse economic impact on businesses, including the ability of California

businesses to compete with businesses in other States. The Executive Officer has

determined that there will be no, or an insignificant, potential cost impact, as defined in

Government Code section 11346.5(a)(9), on private persons or businesses directly

affected as a result of adopting the proposed amendment.

In accordance with Government Code section 11346.3, the Executive Officer has

determined that adoption of the proposed amendment will not affect the creation or

elimination of jobs within the State of California, the creation of new businesses or the

elimination of existing businesses within California, or the expansion of businesses

currently doing business within California.

In accordance with Government Code section 11346.5(a)(11), the Executive Officer

has determined that adoption of the proposed amendment will not have a significant

effect on housing costs.
Impact analysis 26

Finally, the Executive Officer has also determined, pursuant to Government Code

section 11346.5(a)(3)(B), that the proposed regulatory action will not affect small

business, because by itself, the amendment contains no requirements for action and,

therefore, has no direct economic impact.

Before taking final action on the proposed amendment to the regulations, the Board

must determine that no alternative considered by the agency would be more effective in

carrying out the purpose for which the action is proposed or would be as effective and

less burdensome to affected private persons than the proposed action.

C. Alternatives to the Staff’s Proposed Amendments

State law explicitly requires the ARB to assess the contribution of upwind emissions

to downwind ozone concentrations based on the preponderance of evidence, and to

establish transport couples and transport mitigation requirements that are

commensurate with those contributions (Health and Safety Code section 39610(b)).

This mandate precludes consideration of the “no action” alternative with regard to the

proposal for new transport couples, since measured data and not policy determines the

outcome. The identification process leaves little room for alternatives. Each transport

couple is accompanied by discussion of the basis for the identification. Implicit in these

discussions is the consideration of possible alternatives to the transport assessment

classifications, but the available data does not support these alternatives. The staff

considered various alternatives to the mitigation requirements when the regulation was

revised in March 1993. This proposal does not change the requirements; it only

amends the regulation to assign additional responsibilities to previously identified

upwind areas based on new findings of “overwhelming” and “significant” transport.
Recommendations for Further Research 27

CHAPTER V

Recommendations for Further Research

Transport of ozone and precursors is a three-dimensional phenomenon. Surface

transport is only the most obvious process. Mixing of ozone and precursors aloft and

subsequent transport also affects ozone concentrations in downwind and elevated

areas. The routine monitoring networks which supply the data used to assess transport

are primarily surface based. Therefore it has been difficult to understand the full nature

and extent of transport.

Fortunately, two major ozone field studies should provide the three-dimensional data

necessary to fully investigate transport in most of the ozone non-attainment areas of the

State. These studies are the 1997 Southern California Ozone Study (SCOS) (Fujita et

al. 1999a) and the 2000 Central California Ozone Study (CCOS) (Fujita et al. 1999b).

Figure 5 shows the area covered by the two field study domains.

Both studies included enhanced monitoring of meteorology and air quality, both at

the surface and aloft. Data were collected over a large region for several months during

the ozone season, with additional measurements taken during ozone episodes.

These studies were designed to provide the necessary data to support regional

modeling and data analysis efforts, for both attainment planning and transport

assessment. Thus it is anticipated that the resulting data sets and resulting modeling

analyses will allow a unique opportunity to both study and characterize threedimensional transport on a regional basis.
Recommendations for Further Research 28

Figure 5

CCOS and SCOS Domains
References 29

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Transported Air Pollutants Which Contribute to Violations of the State Ambient Air

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Air Resources Board (1990). Assessment and Mitigation of the Impacts of Transported

Pollutants on Ozone Concentrations within California. Staff report prepared by the

Technical Support Division, June 1990.

Air Resources Board (1993a). Assessment and Mitigation of the Impacts of

Transported Pollutants on Ozone Concentrations within California. Staff report

prepared by the Technical Support Division, June 1993.

Air Resources Board (1993b). Public Meeting to Consider the Revision of Emission

Control Requirements to Mitigate the Impact of Transported Pollutants on Ozone

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Air Resources Board (1996). Second Triennial Review of the Assessment of the

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Staff report prepared by the Technical Support Division, November 1996.

Air Resources Board (1998). Proposed Amendments to the Designation Criteria and

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Proposed Maps of the Area Designations for the State and National Ambient Air

Quality Standards. Staff report prepared by the Technical Support Division, August

1998.

Air Resources Board (1998). Emission Inventory 1996. Staff Report prepared by the

Technical Support Division, October 1998.

Air Resources Board (1999). The 1999 California Almanac of Emissions and Air

Quality. Staff report prepared by the Planning and Technical Support Division, 1999.

Fujita, E., M. Green, R. Keislar, D. Koracin, H. Moosmuller, and J. Watson. (1999a).

SCOS97-NARSTO 1997 Southern California Ozone Study and Aerosol Study,

Volume III: Summary of Field Study. February 1999. Prepared by Desert Research

Institute for the ARB.

Fujita, E., R. Keislar, W. Stockwell, H. Moosmuller, D. DuBois, D. Koracin, B. Zielinska,

S. Tanrikulu, and A.J. Ranzieri. (1999b). Central California Ozone Study (CCOS),

Volume I: Conceptual Program Plan Version 2.1. September 1999. Prepared by

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Committees.
References 30

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Main, H. H., L. R. Chinkin, T. L. Haste, P. T. Roberts, and R. Reiss (1997): Shasta

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prepared by Sonoma Technology, Inc. for Shasta County Department of Resource

Management, March 1997.

Niccum, E. M., D. E. Lehrman, and W. R. Knuth (1995). “The Influence of Meteorology

on the Air Quality in the San Luis Obispo County-Southwestern San Joaquin Valley

Region for 3-6 August 1990.” Journal of Applied Meteorology, August 1995, Volume

34, pp. 1834-1847.

San Luis Obispo County Air Pollution Control District (1998). 1998 Clean Air Plan San

Luis Obispo County. San Luis Obispo County Air Pollution Control District, May

1998.

State of California, Department of Finance (1998). County Population Estimates

Components of Change, 1997-1998, with Historical Estimates, 1990-1997.

Sacramento, California. Report E-2, December 1998.

State of California, Department of Finance (1999). City/County Population Estimates,

with Annual Percent Change, January 1, 1998 and 1999. May 1999.
APPENDIX A

TEXT OF HEALTH AND SAFETY CODE
Text of Health and Safety Code A-1

APPENDIX A

TEXT OF HEALTH AND SAFETY CODE

Section 39610

(a) Not later than December 31, 1989, the state board shall identify each air basin,

or subregion thereof, in which transported air pollutants from upwind areas outside the

air basin, or subregion thereof, cause or contribute to a violation of the state ambient air

quality standard for ozone, and shall identify the district of origin of the transported air

pollutants based upon the preponderance of available evidence. The state board shall

identify and determine the priorities of information and studies needed to make a more

accurate determination, including, but not limited to, emission inventories, pollutant

characterization, ambient air monitoring, and air quality models.

(b) The state board shall, in cooperation with the districts, assess the relative

contribution of upwind emissions to downwind ozone ambient air pollutant levels to the

extent permitted by available data, and shall establish mitigation requirements

commensurate with the level of contribution. In assessing the relative contribution of

upwind emissions to downwind ozone ambient air pollutant levels, the state board shall

determine if the contribution level of transported air pollutants is “overwhelming”,

“significant”, “inconsequential”, or some combination thereof. Any determination by the

state board shall be based upon a preponderance of available evidence.

(c) The state board shall make every reasonable effort to supply air pollutant

transport information to heavily impacted districts prior to the development of plans to

attain the state ambient air quality standards, shall consult with affected upwind and

downwind districts, and shall adopt its findings at a public hearing.

(d) The state board shall review and update its transport analysis at least once every

three years.

(e) The state board shall conduct appropriate studies to carry out its responsibilities

under this section.

Section 40918

(a) Each district with moderate air pollution shall, to the extent necessary to meet

the requirements of the plan developed pursuant to Section 40913, include the following

measures in its attainment plan:

(1) A stationary source control program designed to achieve no net increase in

emissions of nonattainment pollutants or their precursors from new or modified

stationary sources which emit or have the potential to emit 25 tons per year or more of

nonattainment pollutants or their precursors. The program shall require the use of best

available control technology for any new or modified stationary source which has the
Text of Health and Safety Code A-2

potential to emit 25 pounds per day or more of any nonattainment pollutant or its

precursors.

(2) The use of reasonably available control technology for all existing stationary

sources, except that stationary sources permitted to emit five tons or more per day or

250 tons or more per year shall be equipped with the best available retrofit control

technology.

(3) Reasonably available transportation control measures sufficient to substantially

reduce the rate of increase in passenger vehicle trips and miles traveled per trip if the

district contains an urbanized area with a population of 50,000 or more.

(4) Provisions to develop areawide source and indirect source control programs.

(5) Provisions to develop and maintain an emissions inventory system to enable

analysis and progress reporting and a commitment to develop other analytical

techniques to carry out its responsibilities pursuant to subdivision (b) of Section 40924.

(6) Provisions for public education programs to promote actions to reduce emissions

from transportation and areawide sources.

(b) Any district with moderate air pollution that is not below the pollutant

concentrations for a moderate classification pursuant to Sections 40921 and 40921.5 by

December 31, 1997, shall comply with Section 40919 if the state board demonstrates

that the additional requirements of Section 40919 will substantially expedite the district's

attainment of the state ambient air quality standards. Any actions taken by the state

board pursuant to this subdivision are

subject to Section 41503.4.

Section 40918.5

(a) Notwithstanding Sections 40918, 40919, and 40920, a district that does not

have extreme air pollution may elect to not include a no-net-increase permitting program

in its attainment plan if all of the following actions are taken:

(1) The governing board of the district finds, at a public hearing, that the no-netincrease permitting program is not necessary to achieve and maintain the state ambient

air quality standards by the earliest practicable date.

(2) Prior to making the finding specified in paragraph (1), the governing board does

both of the following:

(A) Reviews an estimate of the growth in emissions, if any, that is likely to occur as a

result of the elimination of a no-net-increase permitting program.

(B) Complies with Section 40914 either by having adopted, or having scheduled for

adoption, all feasible measures to achieve and maintain state ambient air quality

standards, or by the use of an alternative emission reduction strategy.

(3) The governing board of the district submits its finding to the state board, and,

within 60 days from the date of the submittal of the finding, the state board makes a

determination based on quantifiable and substantial evidence that a no-net-increase

permitting program is not necessary to comply with the mitigation requirements

established pursuant to Section 39610 and that the no-net-increase permitting program

is not necessary to achieve and maintain the state ambient air quality standards by the

earliest practicable date. If the state board does not make any determination within that
Text of Health and Safety Code A-3

60-day period, and the district does not agree to an extension of that time period, the

district may make the election authorized by this subdivision.

(b) Nothing in this section shall relieve a district from the obligation to require the

use of the best available control technology pursuant to Section 40918, 40919, or

40920.

Section 40918.6.

Following the implementation of Section 40918.5, both of the following shall occur:

(1) The district governing board's finding pursuant to paragraph (1) of subdivision

(a) of Section 40918.5 shall, by operation of law, become part of the district's attainment

plan.

(2) The state board shall, during any subsequent review of the district's

attainment plan pursuant to subdivision (a) of Section 41500, determine based on

quantifiable and substantial evidence whether or not a no-net-increase permitting

program is necessary to comply with mitigation requirements established pursuant to

Section 39610 or to achieve and maintain state ambient air quality standards by the

earliest practicable date. If the state board determines that a no-net-increase permitting

program is necessary to comply with those requirements, the district shall then adopt

and implement a no-net-increase permitting program pursuant to Section 40918, 40919,

or 40920.
APPENDIX B

PUBLIC WORKSHOP NOTICE


APPENDIX C

TRANSPORT WORKSHOP PARTICIPANTS
APPENDIX C

TRANSPORT WORKSHOP PARTICIPANTS

(November 4, 1999)

Ann Eli

DTSC

(916) 327-7732

Alex Saschin

Northern Sonoma County

APCD

(707) 433-5911

Randall Woodward

Northern Sonoma County

APCD

(707) 433-5911

Patrick Way

Glenn County APCD

(530) 939-6500

Linsey Marr

UC Berkeley

(510) 642-6582

Robert Nunes

Monterey Bay Unified

APCD

(831) 647-9411

Larry Allen

San Luis Obispo APCD

(805) 781-5912

Paul Allen

San Luis Obispo APCD

(805) 781-5912

Mark Nordheim

Chevron / WSPA

(916) 441-3638

Evan Shipp

San Joaquin Valley

Unified APCD

(559) 230-5809

ARB Attendees

Ken Bowers

John DaMassa

Cynthia Garcia

Steve Gouze

Richard Hackney

Nehzat Motallebi

Debbie Popejoy

Peggy Taricco

Dennis Wade

Jeff Wright
APPENDIX D

GLOSSARY
Glossary D-1

APPENDIX D

GLOSSARY

The following definitions are provided as an aid to the reader.

Adiabat/Adiabatic – see Lapse rate.

APOB – acronym for Airplane observation.

air basin – an area wherein there are similar meteorological and geographic conditions;

also defined by political boundaries; an area in which the air mass is homogeneous;

an area usually bounded by topographical features.

aircraft soundings – temperature and/or pollutant measurements aloft obtained by

aircraft either at multiple levels over one location (referred to as a spiral), at one level

over several locations (referred to as a traverse), or at multiple levels over several

locations (referred to as a dolphin).

airflow charts – the Air Resources Board’s Meteorology Section prepares charts that

include wind speed and wind direction for many sites. The winds are analyzed with

lines showing airflow patterns; a modified streamline chart produced by the Air

Resources Board’s Meteorology Section.

airflow type/pattern – the Air Resources Board’s Meteorology Section first plots wind

speed and direction at various locations statewide, they then analyze the plots using

a modified streamline method, then they categorize, or type, airflow patterns in the

larger, predominant regions of the state.

aloft – above the earth’s surface, generally 50 feet elevation and higher; as opposed to

the surface, is not exactly at the surface but usually anywhere from 2 to 30 feet

above the ground.

ambient – surrounding, on all sides; in situ; for use in air pollution, ambient refers to

free moving air as opposed to, possibly, in a laboratory setting.

anti-cyclonic – clockwise; wind flow around an area of high pressure.

AUSPEX – San Joaquin Valley Air Quality Study/Atmospheric Utility Signatures,

Predictions, and Experiments (SJVAQS/AUSPEX); a field program conducted in

1990.
Glossary D-2

background – for ozone studies, background refers to an area’s normal minimum

ozone concentration, or that concentration normally experienced by an area without

influence or transport from an upwind area. For instance, clean air, such as the air

mass over the Pacific Ocean has a normal background concentration of 4 pphm.

Areas in the mountains may have background concentrations of 5 or 6 pphm

because there is not a presence of NOx for ozone scavenging as there is in the

urban areas. Urban areas often have background ozone concentration levels of 0 or

1 pphm.

backward trajectory – a pictorial technique that estimates the path an air parcel took

over a specified period of time. This path is estimated using wind speed and wind

direction at various sites in the domain, which have been analyzed into successive

hours of wind fields. Terrain and meteorology are also considered in this analysis.

In the case of backward trajectory, the site of the ozone concentration in question is

used as the start point and then a figurative air parcel is “backed up” to determine

the approximate source area of the polluted air mass.

bimodal – an analysis in which there are two areas where a certain value, number, or

concentration occurs with high frequency.

biogenic emissions – hydrocarbon emissions from plant species including alcohols,

acetates, aldehydes, ketones, ethers, esters, alkanes, alkenes, aromatics, and, most

prevalently, isoprene and alpha pinene (a monoterpene).

boundary conditions – for use in photochemical modeling, a boundary condition refers

to those pollutant concentrations in air at the boundaries of the domain being

modeled.

boundary sites – for use in transport assessments, a boundary site is a site close to an

air basin boundary line.

break (inversion) – The temperature at the top of the inversion is an indicator of when

the inversion might cease to exist, or break. This break temperature is the

temperature at which the top of the inversion would be if lowered dry adiabatically.

In other words, as a parcel of air changes altitude, it will warm if lowered or cool if

raised approximately 5F per 1000 feet. When the surface temperature equals or

exceeds that of the inversion top temperature lowered adiabatically, vertical mixing

is possible and the inversion is said to have broken or eroded. Vertical mixing is

contained only in layers of the atmosphere where the temperature decreases with

height.

Clean Air Act – The California Clean Air Act was AB 2595, Sher (Chapter 1568,

Statutes of 1988). Referring only to transport, this Act established time frames by

which districts should improve air quality or meet attainment of the ambient air

quality standard for ozone. This Act also established requirements for transport

assessments to be made as well as updates of these assessments. The Federal
Glossary D-3

Clean Air Act was passed in 1977 and amendments were made in 1990. The state’s

transport research is primarily aligned with the California Clean Air Act.

corridor – a common path of airflow, usually unobstructed and long and usually

transects two air basins.

convection/convective (heating) – upward vertical motion in the atmosphere; free

convection is a result of surface heating or vertical motion caused by density

differences within the airmass; forced convection is a mechanical lifting caused by

such things as weather fronts or terrain.

couple – a pair of geographic areas, one considered upwind and one considered

downwind.

decoupled – occurs when the air mass below the inversion is distinctly different than

the air mass above the inversion.

CDEC – acronym for California Data Exchange Center.

character of exceedance – an ozone concentration trend will indicate whether the

ozone exceedance occurred abruptly or if the ozone concentrations gradually built

up to exceed the state standard. The ozone concentration trend also indicates

whether the exceedance was brief or if it spanned many hours. The ozone

concentration trend for the downwind site, compared with trends for upwind sites,

will help support an assessment of transport or no transport.

CIMIS – acronym for California Irrigation Management Information System.

contours – on constant pressure charts, i.e. 500 millibar chart, a contour is a line of

uniform pressure heights.

confluence – the rate at which adjacent flow is converging, or coming together, along

an axis oriented normal to the flow at the point in question; the opposite of

diffluence; referring to direction.

convergence – flowing or running together to form one mass.

conversions –

To this: From this: m/sec mph knots

m/sec – x 2.2369 x 1.9425

mph x 0.44707 – x 0.86839

knots x 0.51479 x 1.1516 –
Glossary D-4

To this: From this: lbs/day tons/day

lbs/day – x 0.0005

tons/day x 2000 –

To this: From this: °F °C

°F – 0.5555 x (°F-32)

°C 32 + (1.8 x °C) –

cyclonic – counter-clockwise; wind flow around an area of low pressure.

differential heating/cooling – when the rate of heating/cooling differs spatially.

difluence – the rate at which adjacent flow is diverging, or moving apart, along an axis

oriented normal to the flow at the point in question; opposite of confluence; referring

to direction.

disperse – to break up and scatter in all directions; in transport, this term refers to the

scattering of air pollutants by wind or by convection.

diurnal – daily; especially pertaining to actions which are completed within twenty-four

hours and which recur every twenty-four hours.

divergence – flowing or moving apart from one common mass; opposite of

convergence; referring to the velocity field.

domain – a field or sphere of activity or influence; in transport, the domain is the area of

which data is input for modeling purposes.

downwind – The direction toward which the wind is blowing; with the wind.

drainage flow – general term for gravity-induced, down slope flow of relatively cold air.

duration – normally referring to the duration of the ozone exceedance at a particular

site; the number of hours of ozone exceedance can be determined by reviewing the

ozone concentration trend.

eddy – current of air moving against the main current and with a circular motion; limited

in importance or effect.
Glossary D-5

emission inventory – usually expressed in tons per day; the emission inventory is

used in photochemical modeling and in area comparisons.

exceedance – any ozone concentration greater than the ambient air quality standard

for ozone.

extreme concentration – a concentration that is statistically expected to occur less

frequently than once every year.

forward trajectory – a pictorial technique which estimates the path an air parcel took

over a specified period of time. This path is estimated using wind speed and wind

direction at various sites in the domain, which have been analyzed into successive

hours of wind fields. Terrain and meteorology are also considered in this analysis.

In the case of forward trajectory, an upwind area or site is used at the start point and

then a figurative “air parcel” is then moved forward to determine the possible

impacted area.

fumigate – this occurs when an air mass carrying pollutants becomes unstable, causing

the airmass to mix vertically and the pollutants to come in contact with the earth’s

surface.

GMT – acronym for Greenwich Mean Time, the time in Greenwich, England which is

eight hours later than Pacific Standard Time; also referred to as Zulu or Z time.

gradient – usually refers to temperature or pressure change over a given distance

(usually horizontal); the ratio of change to distance. A “tight” or “strong” gradient

refers to a high ratio or a lot of change per given distance. A “loose” or “weak”

gradient, therefore, is less change over the same given distance.

high pressure – a dominating atmospheric feature; a large area where surface

pressures are higher than the surrounding area; an area of anticyclonic circulation.

hydrocarbons – compounds containing various combinations of hydrogen and carbon

atoms and which contribute to ozone formation.

inconsequential – ozone transport classification describing a condition when upwind

emissions were not transported or did not appear to contribute significantly to a

violation of the ozone standard in the downwind area. A violation not impacted by

transported emissions is considered local and results when the wind flow patterns

and atmospheric conditions do not strongly suggest responsibility from an upwind

area. The responsibility of “inconsequential” transport lies with the downwind area.

intrusion – see Stratospheric Intrusion.

inversion – that portion of the vertically measured atmosphere in which the

temperature increases, rather than decreases, with height.
Glossary D-6

inverted (thermal) trough – a low pressure area induced by surface heating in which

the general flow is from east to west instead of west to east; a meteorological feature

commonly found in California from the Imperial Valley northward through the

Sacramento Valley.

isopleth – a line of equal or constant value of a given quantity with respect to either

space or time.

isotherm – a line connecting points of equal temperature.

isobar – a line connecting points of equal pressure.

jet stream – a channel of increased wind speeds. Some low level jets are mechanically

induced such as jets near the inversion or jets funneled by terrain; upper level jet

streams (25,000 to 50,000 feet) are induced by the temperature differences between

two air masses. Jet streams are usually considered as such when they are a

relatively narrow band of greater wind speeds than the surrounding winds and are

greater than 50 knots.

knot – a rate of speed equal to one nautical mile per hour (therefore, no such term as

knots per hour); equal to 1.1508 statute miles per hour or .5144 meters per second.

lapse rate – this is the rate at which a particular column of air cools. A negative lapse

rate indicates warming with height rather than cooling (see inversion). A lapse rate

that equals the standard atmospheric lapse rate is referred to as the adiabatic lapse

rate. A super-adiabatic lapse rate occurs as a layer of air cools with height quicker

than the adiabatic lapse.

latitude – angular distance, measured in degrees (0-90), north or south from the

equator.

lidar – a system which uses laser technology to measure atmospheric parameters.

local – a transport assessment also referred to as “inconsequential”; a transport

assessment given to an exceedance day in which the emission impact from an

upwind district was either non-existent or so little as to have “inconsequential” impact

on the exceedance; a transport assessment in which it has been determined that

nearly all the emissions causing the exceedance were locally generated.

longitude – distance east or west, measured in degrees (0-180), from the prime

meridian (or longitude) which passes through Greenwich, England.

low pressure/heights – on the surface, an area of low pressure is surrounded by an

higher pressures; aloft, an area of low heights is an area where a constant pressure

is lower than the same pressure is in surrounding areas.
Glossary D-7

magnitude – one dimensional; a number given to a quantity for purposes of

comparison with other quantities of the same class.

marine air – air whose characteristics are developed over an extensive water surface

and which, therefore, has the basic maritime quality of high moisture content in at

least its lower levels; below the inversion, moist, thermally modified air intrudes as

far inland as 100 miles or more into most of California.

marine layer - a layer of marine air from the surface to the base of the inversion.

Marta – a system for retrieving and managing various types of meteorological data

including hourly observations and satellite imagery.

microclimate – the fine climatic structure of the air space which extends from the very

surface of the earth to a height where the effects of the immediate character of the

underlying surface no longer can be distinguished from the general local climate;

generally, four times the height of surface growth or structures defines the level

where micro climatic tones disappear.

millibar (MB) – a unit measure of atmospheric pressure. The worldwide average sea

level pressure is 1013.2 MB; 850 MB is approximately 5000 ft; 700 MB is

approximately 10,000 ft; 500 MB is approximately 18,000 ft.

mitigation – in air pollution control, mitigation refers to those measures that are taken

to prevent or reduce emissions in the atmosphere.

mixing depth – the layer of atmosphere, usually surface-based, where vertical mixing

can occur; this depth is usually defined by the inversion.

model – a computer based representation of atmospheric processes.

moderate – regarding the California Clean Air Act, an area classified as moderate for

ozone 1) is expected to reach attainment by December 31, 1997, and 2) has a once

in one year recurrence rate of 12 pphm or less.

nautical mile – 1852 meters, 6076.103 feet, or 1.1508 statute miles; the length of one

minute of arc along any great circle on the earth's surface. This distance varies

slightly with latitude and therefore the distance of a nautical mile has been reached

by international agreement.

nephanalysis – the analysis of a synoptic chart in terms of the types and amount of

clouds and precipitation.

nitric oxides (NO) – a colorless, poisonous gas found in variable trace quantities in the

atmosphere, especially near industrial areas.
Glossary D-8

nocturnal jet – a low-level jet that exists at night due to the strength of the inversion at

that time.

nocturnal – of, done, or happening during the night.

NOx – oxides of nitrogen (NO and/or NO2).

NOx scavenging – a method by which ozone is removed from the ambient air. When

ozone reacts with nitric oxide, the resulting concentration of ozone is lower.

ozone – a secondary ambient air pollutant generated by photochemical reactions

primarily involving hydrocarbons and nitric oxides.

ozone concentrations – produced by the chemical reaction of nitrogen oxides and

hydrocarbons in the presence of sunlight.

overwhelmed – ozone transport classification describing a condition when the

emissions from the upwind area independently result in a violation of the State

ozone standard in the downwind area on any given day. Significant emission

sources in the downwind area were not in the pathway of the air parcel that was

transported from the upwind area. The responsibility for a violation caused by

“overwhelming” transport lies with the upwind area.

Pacific High – a semi-permanent synoptic condition dominating the eastern Pacific.

parcel – a theoretical “box” of air that may be physically tracked to show movement

from an upwind area to a downwind area; a theoretical “box” of air that contains

certain masses of atmospheric gases.

PGM – Photochemical Grid Model; mathematical representation of the threedimensional atmosphere used to simulate the dispersion and chemical

transformation of pollutant emissions that produce ozone.

photochemical – the effect of light or other radiant energy in producing chemical

action; a chemical reaction which involves either the absorption or emission of

radiation.

pibal – contraction for pilot-balloon observation; this type of observation measures

winds aloft by tracking a balloon with a theodolite.

plume – on a point-source scale, a plume is the airborne discharge from an industrial

stack, an agricultural burn location, or any other single source; on a regional scale, a

plume is considered to be the polluted air mass which may travel away from the

source region.
Glossary D-9

ppb – parts per billion; pphm x 10.

pphm – parts per hundred million; ppm x 100.

ppm – parts per million.

precursors – primary air pollutants which contribute to ozone formation; air pollutants

which haven't undergone chemical processes in the ambient air.

preponderance – term used in California Clean Air Act to describe the types and

amount of data used to make transport assessments; greater in amount, weight,

power, influence, importance; predominant.

profiler – equipment that provides continuous winds aloft measurements using the

Doppler shift principle and radar waves.

PST – Pacific Standard Time.

qualification – making a transport assessment using general, relative terms.

quantification – making a transport assessment using specific numbers.

radiosonde – a balloon-borne instrument for the simultaneous measurement and

transmission of meteorological data - specifically pressure, temperature, and

humidity.

RAOB – contraction for radiosonde observation.

rawinsonde – a radiosonde observation combined with a rawin (winds-aloft)

observation; rawin is a method of winds-aloft observation; use of radiosonde to

determine pressure, temperature, dewpoint, wind speed, and wind direction aloft.

reactive hydrocarbons – photochemically reactive compounds that contain only

hydrogen and carbon atoms.

reactive organic gases – photochemically reactive compounds containing carbon,

excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or

carbonates, and ammonium carbonate, and excluding other compounds identified by

the Air Resources Board.

receptor – a downwind area; downwind from the emission source area.

ridge – as a terrain feature, a ridge is the crest line, or the line which joins the highest

peaks of a mountain range, often the air basin boundary; as a meteorological

feature, a ridge is most commonly referred to as a large area of high pressure such

as the “ridging” over the California coastline or a “ridge” of high pressure.
Glossary D-10

Schultz Eddy – counter-clockwise circulation found in the southwestern portion of the

Sacramento Valley. This phenomena is dependent upon wind speed and direction

from the delta area. Very strong southwest windflow will erode the eddy, while very

light windflow will not support the eddy.

sea breeze - air flowing from the ocean to land; usually occurs in late afternoon through

mid evening and the land has become hotter causing air to rise, cooler marine air

will flow landward to replace the air which has risen; see also marine air.

serious – an area that has a once per year recurrence rate greater than or equal to 12

pphm but less than 16 pphm.

severe – an area which has a once in one year recurrence rate greater than or equal to

16 pphm.

significant – ozone transport classification describing a condition in which the

emissions from the upwind area contributed measurably to a violation of the State

ozone standard in the downwind area on any given day, but did not “overwhelm” the

area. A violation is considered caused by “significant” transport if the emissions

from sources within the downwind area combine with the transported parcel carrying

ozone or ozone precursors from the upwind area. A violation classified as

“significant” is considered shared, with responsibility lying with both the upwind and

downwind areas.

sloshing – a theory that polluted air flows up a mountain with the valley breeze in the

afternoon and down the mountain with drainage flow in the late night and early

morning hours leaving behind some of the polluted air near the inversion. The

theory is that this phenomenon may, over several days, contribute to ozone

exceedances.

sounding – this term is used for any type of vertical atmospheric measurement. These

measurement methods include pibals, APOBs, lidar, rawinsonde, and profilers

source area – upwind area; the area from where emissions originate.

spatial – horizontal, geographic relationship.

spirals – vertical aircraft patterns whereby aircraft can measure air pollutants aloft.

stable – when a warm strata of air overlies a cooler strata of air, the condition is

considered stable. Stability is determined by the lapse rate. When a lapse rate is

less than the adiabatic lapse rate (slower cooling with height), the air mass tends to

be more stable. When a lapse rate is more than the adiabatic lapse rate (more

cooling with height), or super-adiabatic, the air mass tends to be less stable. A

stable air mass will have little vertical motion associated with it and will therefore be
Glossary D-11

absent of vertically developed clouds and weather. An unstable air mass will have

greater vertical motion and may have many vertically developed clouds, depending

on the availability of moisture in the air mass.

Stability is very important in assessing air pollution transport and in real-time air

pollution matters such as agricultural burning. Even if there is not enough moisture

for clouds, vertical motion still occurs and will assist in dispersing and diluting the air

pollutants into the atmosphere.

statute mile – the “common” mile; 5,280 feet.

stratosphere – the atmosphere immediately above the tropopause usually beginning

somewhere between 35,000 and 65,000 feet, depending on the latitude and the

season.

stratospheric intrusion – air which is downward vertically mixed from the stratosphere

into the troposphere. This is usually caused by a synoptic disturbance.

streamline analysis – normally, an analysis produced for areas with nearly laminar

flow such as the ocean surface and constant pressure charts (layers aloft); in this

type of analysis, wind vectors are plotted and lines drawn parallel to the vectors;

airflow charts used in transport analyses are sometimes referred to as streamline

charts but are not true streamline charts as such.

subsidence – descending air, usually associated with a high pressure area.

surface – the boundary between the earth and the atmosphere.

surface deposition – method by which ozone and other compounds are removed from

the ambient air. Deposition occurs on vegetation or other surfaces.

synoptic – presenting or involving data on weather and atmospheric conditions over a

wide area at a given time.

theodolite – a piece of survey-type equipment used for tracking weather balloons;

equipment with azimuth (direction) and elevation readings.

thermal low – an area of low atmospheric pressure due to high temperatures caused

by intensive heating at the earth's surface; non-frontal.

thermal trough – see thermal low.

time-series – a graph with hour on the x-axis, ozone concentration on the y-axis; graph

indicates ozone trend for a given period of time.
Glossary D-12

trajectory – the path an air parcel takes in movement from one area to another

dependent upon wind speed, wind direction, terrain, and meteorology; a pictorial

analysis technique which estimates the path an air parcel took over a specified

period of time. This path is estimated using wind speed and wind direction at

various sites in the domain, which have been analyzed into successive hours of wind

fields. Terrain and meteorology are also considered in this analysis. See also

forward and backward trajectory.

transport – horizontal movement of air pollution or air pollution precursors at the earth's

surface or aloft. Vertical movement of air pollution is referred to as mixing.

traverses – horizontal aircraft patterns whereby aircraft can measure air pollutants

spatially.

tropopause – the boundary between the troposphere and the stratosphere.

troposphere – the atmosphere beginning at the earth's surface and extending to the

tropopause.

trough – an area of low pressure (surface) or low heights (aloft); wind flow around a

trough is cyclonic or counter-clockwise.

trof – same as trough.

turbulence – vertical air motion; random motion in layers of a fluid (atmosphere)

UAM – Urban Airshed Model.

upwind – in the direction from which the wind is blowing; against the wind.

UV intensity – solar radiation.

valley breeze – wind flow up a mountain from valley during the day.

vector – wind speed and wind direction combined.

violation – An exceedance that is not excluded as a highly irregular or infrequent event,

such as an exceptional, unusual, or extreme concentration event, and is considered

beyond reasonable regulatory control.

Winds2D – a two-dimensional airflow model used for generating parcel trajectories.

wind – Air in motion relative to surface of the earth; horizontal movement of air

generated and modified by pressure differences, earth's rotation, terrain, synoptic

conditions, latitude; measured or named as direction from which the wind is blowing

such as northerly, southeasterly, valley breeze, sea breeze.
Glossary D-13

wind run – analysis method of algebraically adding wind velocity at a given location;

unreliable analysis method due to inherent assumption of regionally uniform,

unobstructed windflow patterns.

WNI – Weather Network, Inc., a Butte County company providing weather data, historic

and real-time, to contracted users. (Company name recently changed).

Z – Zulu time.

Zulu – see GMT.
APPENDIX E

PROPOSED TEXT OF REGULATION IDENTIFYING AREAS WHICH ARE

IMPACTED BY TRANSPORTED AIR POLLUTANTS
Proposed Text of Regulation E-1

APPENDIX E

PROPOSED TEXT OF REGULATION IDENTIFYING AREAS WHICH ARE

IMPACTED BY TRANSPORTED AIR POLLUTANTS

Amend Subchapter 1.5, Article 5, section 70500, Title 17, California Code of

Regulations to read as follows (items which have been added in previous rulemaking

procedures but subsequently omitted from the California Code of Regulations are in

italics) (proposed additions are underlined and in italics, proposed deletions are struck

out)

1

:

Article 5. Transported Air Pollutants

70500 Transport Identification

(a) Purpose: This regulation identifies the areas in which transported air pollutants

from upwind areas cause or contribute to a violation of the state ambient air

quality standard for ozone and the areas of origin of the transported pollutants.

All areas identified in the table are the air basins except as otherwise specifically

described and defined.

(b) Definitions:

(1) "California Coastal Waters" includes the area between the California

coastline and a line starting at the California-Oregon border at the Pacific

Ocean; thence to 42.0 degrees North, 125.5 degrees West; thence to 41.0

degrees North, 125.5 degrees West; thence to 40.0 degrees North, 125.5

degrees West; thence 39.0 degrees North, 125.0 degrees West; thence to

38.0 degrees North, 124.5 degrees West; thence to 37.0 degrees North,

123.5 degrees West; thence to 36.0 degrees North, 122.5 degrees West;

thence to 35.0 degrees North, 121.5 degrees West; thence to 34.0 degrees

North, 120.5 degrees West; thence to 33.0 degrees North, 119.5 degrees

West; thence to 32.5 degrees North, 118.5 degrees West; and ending at the

California-Mexican border at the Pacific Ocean.

(2) "Upper Sacramento Valley" includes the Colusa, Butte, Glenn, Tehama, and

Shasta County Air Pollution Control Districts, and that area of the Feather

River Air Quality Management District which is north of a line connecting the

northern border of Yolo County to the southwestern tip of Yuba County and

continuing along the southern Yuba County border to Placer County.

(3) "Broader Sacramento Area" includes the Sacramento Metropolitan Air

Quality Management District; Yolo-Solano Air Pollution Control District; the

portions of the El Dorado County Air Pollution Control District included in

1990 U.S. Census Tracts 306.01, 307, 308.01, 308.02, 308.03, 308.04,
Proposed Text of Regulation E-2

309.01, 309.02, 310, 311, 312, 315.01, and 315.02; and the portions of the

Placer County Air Pollution Control District included in 1990 U.S. Census

Tracts 203, 204, 205, 206.01, 206.02, 206.03, 207.01, 207.02, 207.03, 208,

209, 210.01, 210.02, 211.01, 211.02, 212, 213.01, 213.02, 214, 215.01,

215.02, 216, 218.01, and 218.02; and that area of the Feather River Air

Quality Management District which is south of a line connecting the northern

border of Yolo County to the southwestern tip of Yuba County, and

continuing along the southern Yuba County border to Placer County.

(c) Transport Identification Table

OZONE IMPACTED BY TRANSPORT: AREAS OF ORIGIN OF TRANSPORT:

1. North Central Coast San Francisco Bay Area

San Joaquin Valley

2. South Central Coast South Coast

California Coastal Waters

San Joaquin Valley

San Francisco Bay Area

3. South Coast South Central Coast

4. San Diego South Coast

Mexico

5. Upper Sacramento Valley Broader Sacramento Area

6. Broader Sacramento Area San Francisco Bay Area

San Joaquin Valley

7. San Joaquin Valley San Francisco Bay Area

Broader Sacramento Area

8. Great Basin Valleys San Joaquin Valley

9. Mojave Desert South Coast

San Joaquin Valley

Mexico

10. San Francisco Bay Area Broader Sacramento Area

11. Mountain Counties Broader Sacramento Area

San Joaquin Valley

San Francisco Bay Area

12. Salton Sea South Coast

Mexico

13. North Coast San Francisco Bay Area

Note: Authority cited: Sections 39600, 39601, 39610(a), Health and Safety Code.

Reference: Section 39610(a), Health and Safety Code.

 

1. At the May 30, 1996 public hearing, the Air Resources Board approved amendments

to sections 60104 and 60109, and added a new section 60114, Title 17, California Code

of Regulations, which divided the Southeast Desert Air Basin into two new air basins:
Proposed Text of Regulation E-3

the Mojave Desert Air Basin and the Salton Sea Air Basin. These amendments have

not yet been formally approved by the Office of Administrative Law. However, the

transport identification regulation above has been amended to reflect the changes in the

Southeast Desert Air Basin.
Proposed Text of Regulation E-4

PROPOSED TEXT OF REGULATION FOR MITIGATING THE UPWIND EMISSIONS

ON DOWNWIND OZONE CONCENTRATIONS

Amend Subchapter 1.5, Article 6, section 70600, Title 17, California Code of

Regulations, to read as follows (proposed additions are underlined and in italics,

proposed deletions are struck out)1:

ARTICLE 6. Transport Mitigation

70600. Emission Control Requirements

Districts within the areas of origin of transported air pollutants, as identified in

section 70500(c), shall include sufficient emission control measures in their attainment

plans for ozone adopted pursuant to Chapter 10 of the Health and Safety Code, Part 3,

Division 26, beginning with section 40910, to mitigate the impact of pollution sources

within their jurisdictions on ozone concentrations in downwind areas. At a minimum, the

attainment plans for districts within the air basins or areas specified below shall conform

to the following requirements:

(a) Broader Sacramento Area (as defined in section 70500(b)(3)) shall:

(1) require the adoption and implementation of best available retrofit control

technology, as defined in Health and Safety Code section 40406, on all

existing stationary sources of ozone precursor emissions as expeditiously

as practicable. At a minimum, the plan shall provide for the adoption of

rules that represent best available retrofit control technology for source

categories that collectively amount to 75 percent of the 1987 actual

reactive hydrocarbon emissions inventory for permitted stationary sources,

and 75 percent of the 1987 actual nitrogen oxides emissions inventory for

permitted stationary sources, no later than January 1, 1994.

(2) include measures sufficient to attain the state ambient air quality standard

for ozone by the earliest practicable date within the Upper Sacramento

Valley and that portion of the Mountain Counties Air Basin north of the

Calaveras-Tuolumne County border and south of the Sierra-Plumas

County border, except as provided in Health and Safety Code section

41503(d), during air pollution episodes which the state board has

determined meet the following conditions:

(A) are likely to produce a violation of the state ozone standard in the

Upper Sacramento Valley or that portion of the Mountain Counties Air

Basin north of the Calaveras-Tuolumne County border and south of the

Sierra-Plumas County border; and

(B) are dominated by overwhelming pollutant transport from the Broader

Sacramento Area; and
Proposed Text of Regulation E-5

(C) are not measurably affected by emissions of ozone precursors from

sources located within the Upper Sacramento Valley or that portion of

the Mountain Counties Air Basin north of the Calaveras-Tuolumne

County border and south of the Sierra-Plumas County border.

(b) San Francisco Bay Air Basin shall:

(1) require the adoption and implementation of best available retrofit control

technology, as defined in Health and Safety Code section 40406, on all

existing stationary sources of ozone precursor emissions as expeditiously

as practicable. At a minimum, the plan shall provide for the adoption of

rules that represent best available retrofit control technology for source

categories that collectively amount to 75 percent of the 1987 actual

reactive hydrocarbon emissions inventory for permitted stationary sources,

and 75 percent of the 1987 actual nitrogen oxides emissions inventory for

permitted stationary sources, no later than January 1, 1994.

(2) include measures sufficient to attain the state ambient air quality standard

for ozone by the earliest practicable date within the North Central Coast Air

Basin, that portion of Solano County within the Broader Sacramento Area,

that portion of Sonoma County within the North Coast Air Basin, and that

portion of Stanislaus County west of Highway 33, except as provided in the

Health and Safety Code section 41503(d), during air pollution episodes

which the state board has determined meet the following conditions:

(A) are likely to produce a violation of the state ozone standard in the

North Central Coast Air Basin, or that portion of Solano County within

the Broader Sacramento Area, or that portion of Sonoma County within

the North Coast Air Basin, or that portion of Stanislaus County west of

Highway 33; and

(B) are dominated by overwhelming pollutant transport from the San

Francisco Bay Air Basin; and

(C) are not measurably affected by emissions of ozone precursors from

sources located within the North Central Coast Air Basin, or that

portion of Solano County within the Broader Sacramento Area, or that

portion of Sonoma County within the North Coast Air Basin, or that

portion of Stanislaus County west of Highway 33.

(c) San Joaquin Valley Air Basin shall:

(1) require the adoption and implementation of best available retrofit control

technology, as defined in Health and Safety Code section 40406, on all

existing stationary sources of ozone precursor emissions as expeditiously

as practicable. At a minimum, the plan shall provide for the adoption of
Proposed Text of Regulation E-6

rules that represent best available retrofit control technology for source

categories that collectively amount to 75 percent of the 1987 actual

reactive hydrocarbon emissions inventory for permitted stationary sources,

and 75 percent of the 1987 actual nitrogen oxides emissions inventory for

permitted stationary sources, no later than January 1, 1994.

(2) include measures sufficient to attain the state ambient air quality standard

for ozone by the earliest practicable date within the Mojave Desert Air

Basin, the Great Basin Valleys Air Basin, and that portion of the Mountain

Counties Air Basin south of the Amador-El Dorado County border, except as

provided in Health and Safety Code section 41503(d), during air pollution

episodes which the state board has determined meet the following

conditions:

(A) are likely to produce a violation of the state ozone standard in the

Mojave Desert Air Basin, or the Great Basin Valleys Air Basin, or that

portion of the Mountain Counties Air Basin south of the Amador-El

Dorado County border; and

(B) are dominated by overwhelming pollutant transport from the San

Joaquin Valley Air Basin; and

(C) are not measurably affected by emissions of ozone precursors from

sources located within the Mojave Desert Air Basin or the Great Basin

Valleys Air Basin, or that portion of the Mountain Counties Air Basin

south of the Amador-El Dorado County border.

(d) South Central Coast Air Basin south of the Santa Barbara-San Luis Obispo

County border shall, for sources located in that portion of the Basin:

(1) require the adoption and implementation of best available retrofit control

technology, as defined in Health and Safety Code section 40406, on all

existing stationary sources of ozone precursor emissions as expeditiously

as practicable. At a minimum, the plan shall provide for the adoption of

rules that represent best available retrofit control technology for source

categories that collectively amount to 75 percent of the 1987 actual reactive

hydrocarbon emissions inventory for permitted stationary sources, and 75

percent of the 1987 actual nitrogen oxides emissions inventory for permitted

stationary sources, no later than January 1, 1994.

(e) South Coast Air Basin shall:

(1) require the adoption and implementation of best available retrofit control

technology, as defined in Health and Safety Code section 40406, on all

existing stationary sources of ozone precursor emissions as expeditiously

as practicable. At a minimum, the plan shall provide for the adoption of
Proposed Text of Regulation E-7

rules that represent best available retrofit control technology for source

categories that collectively amount to 75 percent of the 1987 actual reactive

hydrocarbon emission inventory of permitted stationary sources, and 75

percent of the 1987 actual nitrogen oxides emissions inventory for permitted

stationary sources, no later than January 1, 1994.

(2) include measures sufficient to attain the state ambient air quality standard

for ozone by the earliest practicable date within the South Central Coast Air

Basin south of the Santa Barbara-San Luis Obispo County border, the San

Diego Air Basin, the Mojave Desert Air Basin, and the Salton Sea Air Basin,

except as provided in Health and Safety Code section 41503(d), during air

pollution episodes which the state board has determined meet the following

conditions:

(A) are likely to produce a violation of the state ozone standard in the South

Central Coast Air Basin south of the Santa Barbara-San Luis Obispo

County border, or in the San Diego Air Basin, or in the Mojave Desert

Air Basin, or in the Salton Sea Air Basin; and

(B) are dominated by overwhelming pollutant transport from the South

Coast Air Basin; and

(C) are not measurably affected by emissions of ozone precursors from

sources located within the South Central Coast Air Basin south of the

Santa Barbara-San Luis Obispo County border, or the San Diego Air

Basin, or the Mojave Desert Air Basin, or the Salton Sea Air Basin.

Note: Authority cited: Sections 39601 and 39610(b), Health and Safety Code.

Reference: Sections 39610, 40912, 40913, 40921 and 41503, Health and Safety

Code.

 

1. At the May 30, 1996 public hearing, the Air Resources Board approved amendments

to sections 60104 and 60109, and added a new section 60114, Title 17, California Code

of Regulations, which divided the Southeast Desert Air Basin into two new air basins:

the Mojave Desert Air Basin and the Salton Sea Air Basin. These amendments have

not yet been formally approved by the Office of Administrative Law. However, the

transport identification regulation above has been amended to reflect the changes in the

Southeast Desert Air Basin.
Technical Support for Assessments F-1

APPENDIX F

TECHNICAL SUPPORT FOR ASSESSMENTS
Technical Support for Assessments F-1

1. Broader Sacramento Area to Upper Sacramento Valley

The ARB staff screened 1997 and 1998 ozone exceedances (1996 data have been

independently evaluated by Sonoma Technology Inc.) and identified three possible local

days. These proposed local exceedances occurred on August 4, 1997, August 19,

1998, and September 24, 1998. The analysis of each of the three exceedance days

began with the first “clean” day (maximum ozone concentration between 0.004 parts per

million (ppm) and 0.085 ppm) prior to the exceedance.

Air quality and meteorological data were evaluated for evidence of transport impacts.

(See Figure F-1 for the location of the monitoring sites, pertinent cites, and counties.)

Both spatial and temporal analyses were done to establish the extent of the

exceedances and the time of day that they occurred. Diurnal profiles represent the

ozone concentrations that occurred throughout the day and were used to understand

the behavior of the ozone concentrations. Maximum concentrations occuring in the

early morning may indicate the possibility of ozone trapped aloft which fumigates to the

surface as the surface temperatures increase. Maximum concentrations occuring in the

evening may indicate ozone transported from upwind sources. In general, exceedances

caused by locally generated emissions usually peak around late morning or early

afternoon in the middle of summer, between the hours of 1100 and 1400 PST. During

late summer and the beginning of fall, locally generated ozone usually peaks later,

between the hours 1200 and 1500 PST.

The assessment of transport impacts requires a three dimensional analysis.

Therefore, air quality and meteorological data for different altitudes is helpful in

understanding the possibility of transport of air pollutants aloft. The monitors located on

top of the Sutter Buttes and Tuscan Buttes in the Sacramento Valley area represent the

air quality aloft. Sutter Buttes is located at 2,132 feet in Sutter County and Tuscan

Buttes is at 1,868 feet in Tehama County.

a. Emissions

Shasta County is the second highest emitter of NOx and ROG within the Sacramento

Valley Air Basin (SVAB), with Sacramento County being the highest (see Table F-1).

The highest emitting facilities of NOx in the SVAB are located in Shasta County

(see Table F-2). The highest emitter of NOx within the SVAB is Calaveras Cement

Company with 559 tons/year located in the city of Redding. Three other high emitting

facilities of NOx within the SVAB are located in the city of Anderson: Simpson Paper

Company with 377 tons/year, Wheelabrator Energy with 364 tons/year, and

Wheelabrator Lassen with 227 tons/year. In addition, the city of Burney has one of the

highest emitting facilities for NOx, the PG&E plant producing 220 tons/year.
Technical Support for Assessments F-2

Figure F-1

Counties, Monitoring Sites, and Cities
Technical Support for Assessments F-3

Table F-1

1996 Emissions of the Upper Sacramento Valley and Broader Sacramento Area

Area NOx

(tons/day)

ROG

(tons/day)

Upper Sacramento Valley (USV)

Butte County 20 26

Colusa County 12 9.3

Glenn County 11 9.6

Shasta County 31 28

Sutter County (USV portion) 9.9* 13*

Tehama County 17 10

Yuba County 8.5 9.2

Broader Sacramento Area (BSA)

El Dorado County (BSA portion) 13* 18*

Placer County (BSA portion) 24 25

Sacramento County 86 100

Solano County (BSA portion) 13 16

Sutter County (BSA portion) - -

Yolo County 18 20

* Sutter County and El Dorado County are divided for transport and

planning proposes. The emission inventory does not calculate

these as separate portions. Most of the anthropogenic emissions in

Sutter County are produced in the portion within the USV.

Therefore, Sutter County's total emissions are allocated to the USV.

In El Dorado County most of the anthropogenic emissions are

produced in the portion within the BSA. Therefore, El Dorado

County's total emissions are allocated to the BSA portion.
Technical Support for Assessments F-4

Table F-2

The Eight Highest Emitting Facilities of NOx Emissions in the Sacramento Valley

Air Basin (Based on 1995 Emissions)

County City Facility Emissions

(tons/year)

Shasta Redding Calaveras Cement 559

Shasta Anderson Simpson Paper Company 377

Shasta Anderson Wheelabrator Energy 364

Yolo Woodland Spreckels Sugar Company 275

Yolo Woodland Contadina Foods Inc. 269

Butte Oroville Louisiana Pacific Corp. 236

Shasta Anderson Wheelabrator Lassen 227

Shasta Burney PG&E 220

b. Population

Shasta County has the second highest population in the USV, second to Butte

County. Shasta County's immediate neighboring counties to the south are Tehama and

Butte County. Together these three counties constitute approximately 70 percent of the

USV population with a total 1998 population of 418,100. The average growth for these

three counties between 1990-1998 was 10 percent. Table F-3 shows the population

growth in the USV.

Table F-3

Population of Upper Sacramento Valley

Area 1990 1995 1998 % Growth

1990 - 1998

Butte County 183,100 194,700 199,100 8.7%

Colusa County 160,400 17,700 18,600 13.4%

Glenn County 24,900 26,350 26,850 7.8%

Shasta County 148,600 160,300 164,100 10.4%

Sutter County (USV portion) 65,000* 73,000* 76,400* 17.5%

Tehama County 49,900 53,800 54,900 10.0%

Yuba County 58,800 62,100 60,800 3.4%

* The Department of Finance does not calculate a population number for the

USV portion of Sutter County. Since the majority of the population is located in

the USV portion all of Sutter County's population is allocated to the USV.
Technical Support for Assessments F-5

c. Analysis of the August 4, 1997 Exceedance

Air Quality

Shasta County exceeded the State ozone standard on August 4, 1997, with a daily

maximum concentration of 0.097 ppm. The analysis included data for the period of

August 2, 1997, through August 4, 1997. The air quality for the entire Sacramento

Valley Air Basin (SVAB) was reviewed for spatial and temporal relationships. Table F-4

shows the daily maximum 1-hour ozone concentration and the time the maximum ozone

concentration occurred for the significant sites in the SVAB.

Table F-4

Air Quality for August 2-4, 1997

August 2 August 3 August 4

Monitoring Site

Max

Ozone

(ppm)

Hour

of

Max

PST

Max

Ozone

(ppm)

Hour

of

Max

PST

Max

Ozone

(ppm)

Hour

of

Max

PST

Shasta County

 Redding 0.082 1200 0.077 1300 0.097 1200

 Anderson 0.052 1200 0.053 1100 0.075 1200

Tehama County

 Tuscan Buttes 0.063 1100 0.069 1500 0.065 2100

 Red Bluff 0.060 1000 0.060 1000 0.070 1300

Butte County

 Chico-Manzanita 0.056 1200 0.058 1500 0.059 1300

Glenn County

 Willows 0.057 1100 0.056 1100 0.066 1200

Sutter County

 Sutter Buttes 0.054 1200 0.070 1900 0.071 1400

Colusa County

 Colusa 0.056 1100 0.064 1500 0.076 1700

Placer County

 Rocklin 0.067 1400 0.077 1200 0.050 0900

Sacramento County

 Sloughhouse 0.057 1400 0.067 1500 0.098 1200

 Earhart 0.079 1600 0.092 1500 0.085 1100

* Ozone Concentrations exceeding the State standard are shaded and bold

faced

The exceedance in Shasta County occurred at 1200 PST, indicating contribution

from locally generated emissions. In addition, the concentrations at Tuscan and Sutter

Buttes were low and did not appear to contribute significantly to the exceedance. The

ozone concentration range was 0.062 ppm - 0.070 ppm for the Sutter Buttes site the
Technical Support for Assessments F-6

evening prior to the exceedance day between the hours of 1400 and 2000 PST. The

ozone concentration range was 0.057 ppm - 0.064 ppm for the Tuscan Buttes site the

morning of the exceedance day between the hours 300 and 1000 PST. These

concentrations indicate no significant contribution to Shasta County exceedance from

BSA transport aloft.

Meteorology

The surface winds were affected by a high pressure system located at the most

northern extent of the Sacramento Valley (Shasta County), and a low pressure system

located over most of the remainder of the Sacramento Valley. (High-pressure systems

are conducive for ozone formation, whereas, low-pressure systems are conducive for

the dispersion, and dilution of emissions and pollutant concentrations.) The presence

and location of these two pressure systems caused a weak marine layer throughout the

period, with a weak surface southerly flow in the Sacramento Valley. For most of this

period, there were weak northerly surface winds in the northern portion of the USV.

During the afternoon of August 3, 1998, there were lighter southeast winds. On August

4, 1998, the northerly winds remained all day. Moreover, an early morning calm was

observed for each of these three days, allowing local emissions to build. These

meteorological conditions, i.e.-week southerly flow, northerly winds, and morning calm,

are not conducive for surface transport from the BSA to Shasta County.

The aloft winds were also affected by these two pressure systems. The day prior to

the exceedance, the wind direction at Sutter Buttes for the evening hours between 1400

and 2000 PST was from the south and the wind speed was very low (1 mile per hour).

In addition, the wind direction at the Tuscan Butte site for the morning hours between

300 and 1000 PST was from the north and the wind speed was 4 miles per hour. The

aloft wind directions and speeds are not conducive for the transport of significant

pollutants from the BSA to Shasta County.

d. Analysis of the August 19, 1998 Exceedance

Air Quality

This ozone exceedance was similar to the August 4, 1997 exceedance. Shasta

County exceeded the State ozone standard on August 19, 1998 with a daily maximum

concentration of 0.100 ppm. The analysis included data for the period of August 17,

1998 through August 19, 1998. Air quality for the entire SVAB was reviewed for spatial

and temporal relationships. Table F-5 shows the daily maximum 1-hour ozone

concentration and the time the maximum occurred at significant sites in the SVAB.

For the duration of this period, Shasta County was the only area within the SVAB

that exceeded the State ozone standard. The exceedance occurred at 1300 PST,

indicating contribution from locally generated emissions. In addition, the aloft

concentrations at Tuscan and Sutter Buttes were low and did not appear to contribute

significantly to the exceedance. Between the hours of 1400 and 2000 PST on the
Technical Support for Assessments F-7

evening prior to the exceedance day, the ozone concentration range was

0.059-0.065 ppm at the Sutter Buttes site. Between the hours of 300-1000 PST of the

exceedance day, the ozone concentration range was 0.048-0.059 ppm for the Tuscan

Buttes site. These concentrations indicate no significant contribution to the Shasta

County exceedance from BSA transport aloft.

Table F-5

Air Quality for August 17-19, 1998

August 17 August 18 August 19

Monitoring Site

Max

Ozone

(ppm)

Hour

of

Max

PST

Max

Ozone

(ppm)

Hour

of

Max

PST

Max

Ozone

(ppm)

Hour

of Max

PST

Shasta County

 Redding 0.080 1100 0.090 1200 0.100 1300

 Anderson 0.070 1200 0.080 1600 0.080 1100

Tehama County

 Tuscan Buttes 0.074 1700 0.079 1600 0.073 1400

 Red Bluff 0.080 1700 0.080 1600 0.070 1200

Butte County

 Chico-Manzanita 0.065 1700 0.063 1500 0.073 1700

Glenn County

 Willows 0.069 1400 0.064 1500 0.075 1500

Sutter County

 Sutter Buttes 0.072 1400 0.065 1600 0.079 1700

Colusa County

 Colusa 0.069 1600 0.063 1600 0.074 1600

Placer County

 Rocklin 0.061 1600 0.053 1500 0.072 1400

Sacramento County

 Folsom 0.062 1600 0.063 1700 0.070 1400

 Sloughhouse 0.062 1500 0.062 1700 0.080 1600

* Ozone Concentrations exceeding the State standard are shaded and bold

faced

Meteorology

The surface winds for this three day period were affected by a shifting surface high

pressure system located near or around the most northern extent of the Sacramento

Valley (Shasta County), and a surface low pressure system located over most of the

remainder of the Sacramento Valley. (High-pressure systems are conducive for ozone

formation, whereas, low-pressure systems are conducive for the dispersion and dilution

of emissions and pollutant concentrations.) This high and low system persisted

throughout the period. The presence and location of these two pressure systems
Technical Support for Assessments F-8

seemed to have weakened and decoupled the winds. Thus, a southerly flow was not as

conducive for surface transport from the BSA. In addition, an early morning calm or

northerly wind was observed for each of the three days, allowing local emissions to

build or potentially to recirculate.

The aloft winds were also affected by these two pressure systems. For the evening

hours between 1400 and 2000 PST on the day prior to the exceedance, the wind

direction at Sutter Buttes was from the south and the wind speed was very low (3 miles

per hour). For the morning hours between 300 and 1000 PST, the wind direction at the

Tuscan Buttes site was from the north and the wind speed was 5 miles per hour. These

aloft wind directions and speeds are not conducive for the transport of pollutants from

the BSA to Shasta County.

e. Analysis of the September 24, 1998 Exceedance

Air Quality

Shasta County exceeded the State ozone standard on September 24, 1998, with a

daily maximum concentration of 0.100 ppm. The analysis included data for the period

of September 21, 1998, through September 24, 1998. The air quality for the entire

SVAB was reviewed for spatial and temporal relationships. Table F-6 shows the daily

maximum 1-hour ozone concentration and the time the maximum occurred at significant

sites in the SVAB.

For the duration of this period, Shasta County was the only area within the SVAB

that exceeded the State ozone standard. The exceedance occurred at 1500 PST,

indicating contribution from locally generated emissions from within Shasta County,

where some emissions from adjacent counties within the USV could have contributed.

The aloft concentrations at Tuscan and Sutter Buttes were low. The maximum

concentrations at the monitors on the Tuscan and Sutter Buttes occurred at the same

time as the maximum concentration at Redding. Between the hours 1400 and 2000

PST of the evening prior to the exceedance day, the ozone concentration range for the

Sutter Buttes site was 0.052-0.064 ppm. Between the hours 300 and 1000 PST during

the early morning of the exceedance day, the ozone concentration range for the Tuscan

Buttes site was 0.046-0.055 ppm. This indicates that the ozone aloft did not appear to

contribute significantly to the exceedance.

Meteorology

During this period, Shasta County had higher ambient temperatures than in

Sacramento County. This indicates that Shasta County's temperature was more

conducive for ozone formation. In addition, the lower temperatures observed in

Sacramento County may help, in part, explain the low ozone concentrations during this

period in the Sacramento County area.
Technical Support for Assessments F-9

Table F-6

Air Quality for September 24, 1998

September 21 September 22 September 23 September 24

Monitoring Site

Max

Ozone

(ppm)

Hour

of

Max

PST

Max

Ozone

(ppm)

Hour

of

Max

PST

Max

Ozone

(ppm)

Hour

of

Max

PST

Max

Ozone

(ppm)

Hour

of

Max

PST

Shasta County

 Redding 0.060 1200 0.090 1600 0.090 1200 0.100 1500

 Anderson 0.050 1200 0.080 1500 0.080 1400 0.070 1700

Tehama County

 Tuscan Buttes 0.060 2000 0.080 1800 0.075 1400 0.074 1500

 Red Bluff 0.060 1400 0.070 1300 0.080 1500 0.070 1200

Butte County

 Chico-Manzanita 0.056 1500 0.075 1500 0.053 1400 0.071 1500

Glenn County

 Willows 0.063 1500 0.069 1500 0.055 12:00 0.069 1500

Sutter County

 Sutter Buttes 0.078 1500 0.072 1500 0.064 1700 0.077 1500

Colusa County

 Colusa 0.055 1300 0.067 1600 0.056 1600 0.070 1500

Placer County

 Rocklin 0.064 1500 0.063 1600 0.046 1300 0.061 1500

Sacramento County

 Sloughhouse 0.060 1600 0.067 1600 0.057 1400 0.065 1500

 Folsom 0.073 1500 0.070 1600 0.053 1700 0.064 1400

* Ozone Concentrations exceeding the State standard are shaded and bold faced

On September 21, 1998, a northerly wind was prevalent for most of the day, which

allowed for the clean day in the SVAB. The period from September 22-24 had very

similar meteorological conditions. During all three days, a weak marine layer created a

weak southerly flow throughout the Valley. As the day reached the highest ambient

temperature in Shasta County, the weak southerly flow reached the Redding area and

some contribution from the Upper Sacramento Valley (USV) was observed. An evening

and early morning calm was observed for each of the last three days, allowing local

emissions to build.

During the last three days of this period, the highest ozone concentration occurred

about the same time as the daily temperature peaked. The temperature peaked at 27°C

in Redding, and peaked at 24.9°C in Folsom. The wind trajectory model runs were

consistent with the above analysis, indicating that the emissions which impacted the

Redding monitor most likely originated in Tehama and Shasta Counties.
Technical Support for Assessments F-10

2. San Francisco Bay Area Air Basin to North Coast Air Basin

In 1999, the Sonoma County portion of the NCAB (northern Sonoma County) was

designated nonattainment for the State ozone standard for the first time. As a newly

designated nonattainment area with few stationary sources and low vehicle volumes,

the staff believed that a transport assessment was necessary.

There were nine exceedance days measured in Healdsburg during 1996-98. (See

Figure F-2 for the locations of monitoring sites, pertinent cities, and counties.) Four of

these days can be excluded as extreme concentrations and are depicted in Table F-7.

(An extreme concentration is a concentration that is statistically expected to recur less

frequently than once every year.) Exceedances identified as extreme concentrations

are not considered violations and were not included in this transport assessment

because attainment designations are based only on violations. Those days not

considered extreme concentration events are violations days. The staff analyzed all five

violation days and found all five violation days to be ”overwhelmed” by transport of

ozone and/or ozone precursor emissions from the SFBAAB. The September 24, 1997,

exceedance is presented as an example of an exceedance due to “overwhelming”

transport.

Table F-7

Healdsburg Ozone Exceedances (1996-98)

Date

Maximum Ozone

Concentration

 (ppm)

Hour(s) of Maximum

Ozone

Concentration

(PST)

Extreme

Concentration?

9/24/97 0.10 1400 – 1700 No

9/29/97 0.10 1200 No

8/3/98 0.10 1200 No

9/1/98 0.10 1300 No

9/2/98 0.12 1400 Yes

9/3/98 0.13 1300,1500 Yes

9/7/98 0.11 1200,1400,1500 Yes

9/11/98 0.10 1300 – 1500 No

9/12/98 0.11 1300 Yes

a. Emissions

The staff used the 1996 emission inventory data for statewide, air basin, and county

totals. While such emission totals provide only general information, they are useful for

determining the relative difference in emissions between various areas. Table F-8

illustrates the wide disparity between emission inventories in the SFBAAB and the

NCAB. Emissions in the SFBAAB for both NOx and ROG are roughly ten times greater

than that of the NCAB. Emissions in the Sonoma County portion of the SFBAAB are

about 3-4 times greater than the Sonoma County portion of the NCAB. Emissions from
Technical Support for Assessments F-11

Figure F-2

Counties, Monitoring Sites, and Cities
Technical Support for Assessments F-12

the northern counties of the SFBAAB (southern Sonoma, Marin, and Napa Counties)

are about 7 times greater than in northern Sonoma County. Additionally, there are no

major stationary sources of ROG or NOx between the basin boundary and the

Healdsburg monitor.

Table F-8

1996 Basin and County Emissions (Tons/Day)

North Coast Air Basin

County NOx ROG

Del Norte 3.6 6

Humboldt 23 23

Mendocino 15 16

Sonoma15.8 9.9

Trinity 2.9 6.1

Total250 61

San Francisco Bay Area Air Basin

County NOx ROG

Alameda 110 100

Contra Costa 120 91

Marin 17 21

Napa 8.3 11

San Francisco 38 42

San Mateo 62 52

Santa Clara 120 110

Solano136 32

Sonoma126 29

Total2540 490

1

That portion of the county within the air

basin.

2 Air basin emission total may not equal the

sum of the county emission totals because

of rounding.

b. Population

Healdsburg, with a mere population of 10,000, is located just five miles north of the

basin boundary separating the SFBAAB and the NCAB. In addition, Healdsburg is only

approximately 15 miles north of Santa Rosa, a fast growing metropolitan area with an

estimated population of 140,000. Windsor, an area of new development, is a town 10

miles north of Santa Rosa and only two miles south of the basin boundary. Windsor’s
Technical Support for Assessments F-13

population is estimated to be 20,000. The population of Sonoma County south of the

basin boundary (the SFBAAB portion) is approximately seven times greater than its

northern counterpart (the NCAB portion). In addition, the combined population of the

SFBAAB portion of Sonoma County, Marin County, and Napa County is more than 13

times greater than the population of northern Sonoma County. Finally, the population of

the entire SFBAAB is approximately 20 times greater than the NCAB.

c. Analysis of the September 24, 1997 Exceedance

Air Quality

The maximum ozone concentrations for the days leading up to the exceedance at

Healdsburg on September 24, 1997 are shown in Table F-9. Ozone maximums on

September 22 were very low (near background levels) except at Healdsburg which

recorded 0.07 parts per million (ppm). Ozone concentrations in Healdsburg and

southward increased about 0.02 – 0.04 ppm on September 23. The upward trend

continued on September 24, 1997, when Healdsburg exceeded the State ozone

standard with a 0.10 ppm for four consecutive hours. On this day, high ozone values

were observed from San Rafael to Healdsburg. The exceedance at Healdsburg lasted

until 1700 Pacific Standard Time (PST) which is an indication that the ozone

concentrations may be impacted by transport. Maximum ozone concentrations in an

area resulting from ‘local emissions’ typically occur between 1100 and 1400 local

standard time (LST). Although, as seen in Table F-7, the timing of most of Healdsburg’s

exceedances might appear to indicate that their exceedances are caused by local

emissions. However, as already mentioned, the emissions in Healdsburg are minimal.

The fact that Healdsburg is only 15 miles downwind of Santa Rosa is the primary

reason for their early exceedance hours. Only a small amount of time is typically

needed for ozone and ozone precursors to be transported from Santa Rosa to

Healdsburg.

Meteorology

Surface wind observations along the transport route from the SFBAAB to

Healdsburg predominantly measured wind coming from a southerly direction from

September 22 up until the exceedance at 1400 PST on September 24. Sites recording

south winds include Petaluma, Santa Rosa, Windsor, and Healdsburg. These sites are

shown in Figure F-2.

Surface wind trajectories were simulated for this episode. One-day forward and

backward trajectories were calculated for both September 23 and September 24. Both

the forward and backward trajectories consistently point toward the Santa Rosa area as

the upwind area contributing to Healdsburg’s ozone concentrations. Two-day

trajectories indicate that the Santa Rosa area and possibly areas to the south

contributed to Healdsburg’s ozone concentrations. Therefore, it is possible that carryover emissions from areas south of Santa Rosa may have also contributed to

Healdsburg’s ozone exceedances.
Technical Support for Assessments F-14

Table F-9

Maximum Ozone Concentrations (September 22-24, 1997)

September 22 September 23 September 24

Site Max

Ozone

(ppm)

Hour(s) of

Max

Max

Ozone

(ppm)

Hour(s) of

Max

Max

Ozone

(ppm)

Hour(s) of

Max

Marin County

 San Rafael 0.036 1400 0.077 1300 0.106 1400

Sonoma County

 Santa Rosa 0.047 1400 0.077 1500 0.093 1400

 Healdsburg 0.070 1400-1500 0.090 1400-1500 0.100 1400-1700

Napa County

 Napa 0.039 1500 0.075 1300 0.084 1300

Mendocino County

 Ukiah 0.051 1300 0.051 1300 0.067 1600

* Ozone Concentrations exceeding the State standard are shaded and bold faced

The staff also examined upper-level winds for indications of transport. The upper air

meteorological sites that were analyzed include the Oakland (and Reno) rawinsonde

(available twice a day), profiler data located at Bodega Bay (hourly), and pibal data from

Sacramento (once a day). In addition, hourly wind data from surface sites located on

mountain peaks were used to approximate upper level winds at their corresponding

elevations. These sites include PG&E Geyser sites 13 (3300 feet) and 17 (3040 feet),

Mt. Tamalpais (2500 feet), Kregor Peak (1895 feet), Chabot (560 feet), Pt. San Pablo

(230 feet), and Sutter Buttes (2130 feet) and are shown in Figure F-2. The Sutter

Buttes site also measures ozone and can be used to estimate ozone aloft.

For the hours leading up the exceedance in Healdsburg on September 24, 1997,

winds aloft were generally southeasterly and easterly. Therefore, the immediate upwind

region is the SFBAAB. Additional upper air meteorological and air quality data would be

needed to implicate further upwind areas such as the Broader Sacramento Area or the

San Joaquin Valley Air Basin.
Technical Support for Assessments F-15

3. San Francisco Bay Area and San Joaquin Valley Air Basins to South Central

Coast Air Basin (San Luis Obispo County)

A transport assessment was conducted for San Luis Obispo County (the County) at

the request of the San Luis Obispo County Air Pollution Control District (the District).

This request was due to an unusually high number of State 1-hour ozone exceedances

in 1998. 1998 was the worst year on record with 25 ozone exceedance days.

The County is located in the northern section of the South Central Coast Air Basin

(SCCAB). (See Figure F-3 for a map of the area.) Monterey County borders it to the

north, Santa Barbara County to the south, the Pacific Ocean to the west, and the San

Joaquin Valley to the east. The County consists of three geographic regions:

(1) The coastal plateau along the Pacific Ocean having 75% of the population and

producing the highest emissions in the county;

(2) The upper Salinas River valley in the northern section of the county having 23%

of the population and historically measuring the highest ozone levels in the

county; and

(3) The east county plain has only 2% of the county’s population and the largest land

area, which consists mostly of the Carrizo Plain, a large drainage basin. The

Carrizo Plain borders the Temblor Mountain range to the east, which lies in a

northwest-southeast direction along the western side of the SJVAB. The only

major break in the range occurs at the Cholame Pass (elevation 1155 feet) in the

northern end of the mountain range.

The meteorology of the County, San Francisco Bay Area Air Basin (SFBAAB), North

Central Coast Air Basin (NCCAB), and the San Joaquin Valley Air Basin (SJVAB) is

highly influenced by the existence of a persistent high pressure area residing over the

Pacific Ocean. Seasonal variations in the strength and location of the high pressure

system along with circulations driven by land and sea temperature differences affect the

local winds. The typical summer wind circulation pattern in the County consists of the

daily sea breeze meeting the wind flow coming out of the San Joaquin Valley and

coming southward up the Salinas River Valley, which peaks in the late afternoon. When

the high pressure area moves inland, it causes air to sink and heat as it descends in the

atmosphere. This heating aloft causes an elevated layer of air to be warmer than the air

underneath and subsequently prevents any vertical mixing of air. The normal sea

breeze pattern is shut down and stagnant conditions persist. Under stronger offshore

flow SLOC can be impacted by airflow from the north and east.

All 1996 through 1998 ozone exceedance days were first screened to determine

which were violations of the State Ambient Air Quality Standard using the criteria for

extreme concentrations. All the violation days were examined with the focus on

analyzing examples of “overwhelming”, “significant”, and “inconsequential” ozone

transport. Ozone episodes were identified that represented each of the three kinds of

transport impacts.
Technical Support for Assessments F-16

Figure F-3

Counties, Monitoring Sites, and Cities
Technical Support for Assessments F-17

a. Emissions

Comparisons of the 1996 emission inventories for ozone precursors were conducted

for San Luis Obispo County, neighboring counties, and air basins and are presented in

Table F-10. While such emission totals provide only general information, they are

useful for determining the relative difference in emissions between various areas.

Table F-10 illustrates the wide disparity between emission inventories in the County and

other areas. The NOx emissions in NCCAB, southern SFBAAB, SJVAB, and Monterey

plus San Benito Counties are nearly 2 to 15 times the emissions generated in the

County. The ROG emissions in NCCAB, southern SFBAAB, SJVAB, and Monterey

plus San Benito Counties are nearly 2 to 17 times the emissions generated in the

County. The combined emissions of central and southern SJVAB are 4-6 times the NOx

and 4-7 times the ROG inventories of the County. These emission inventory

relationships indicate that emissions in adjacent areas, under appropriate

meteorological conditions, have the potential to significantly and overwhelmingly impact

the County.

Table F-10

1996 Emission Inventories of Ozone Precursors

Emissions (tons/day) Ratio to SLOC Area ROG NOx ROG NOx

North Central Coast 73 73 2.5 2.2

Monterey + San Benito Counties 49 56 1.7 1.7

Southern San Francisco Bay Area 395 450 13.6 13.6

San Joaquin Valley 490 500 16.9 15.2

Southern San Joaquin Valley 130 150 4.5 4.5

Central San Joaquin Valley 203 195 7 5.9

San Luis Obispo County 29 33 1 1

b. Population

The population distribution of San Luis Obispo County follows closely the three

geographic regions as explained in Section 3 and is found in Table F-11. Population

growth for the entire county was 4.6% between 1990 and 1995. The population rose

from 217,162 to 227,225 during this period. The greatest increase in population

occurred in the upper Salinas Valley area. However, this growth represents less than

4,000 residents.

Population growth in the surrounding air basins has increased from 1990 to 1995.

The greatest population growth was within the SJVAB.
Technical Support for Assessments F-18

Table F-11

Population Growth

Area 1990 1995 Population

Difference % Growth

San Luis Obispo County 217,162 227,225 10,063 4.6

Coastal Plateau 114,874 116,802 1,928 1.7

San Luis Obispo Area 43,478 43,252 -226 -0.5

Morro Bay Area (Estero) 27,515 27,764 249 0.9

San Luis Bay Area 43,881 45,786 1,905 4.3

Upper Salinas Valley Area 52,177 56,010 3,833 7.4

Atascadero 22,876 23,962 1,086 4.8

Paso Robles 18,529 20,020 1,491 8.1

San Miguel 1,123 1,200 77 6.9

Santa Margarita 1,066 1,208 142 13.3

Templeton 2,795 3,173 378 13.5

Rural Area 5,788 5,961 173 3.0

Shandon-Carrizo 1,902 2,407 505 26.6

San Joaquin Valley 2,660,000 2,960,000 300,000 11.3

San Francisco Bay Area 5,900,000 6,240,000 340,000 5.8

North Central Coast 624,800 645,950 21,150 3.4

c. “Overwhelming” and “Significant” Transport Impact – August 28, 1998

Air Quality

The maximum ozone concentrations for the days leading up to the exceedances at

Paso Robles and Atascadero on August 28 are shown in Table F-12. The ozone air

quality on August 26 was good except in the isolated areas in central and southern

SJVAB. On August 27 ozone maximum concentrations increased at Paso Robles and

Atascadero, as well as aloft at Black Mountain (the District’s special study air monitoring

site at 3600 feet) and the adjacent air basins. The ozone concentrations continued to

increase on August 28, when both Paso Robles and Atascadero exceeded the State

ozone standard. The August 28 State ozone exceedances at Paso Robles occurred

during two periods, 1200-1500 and 1800-2000 PST with the daily maximum occurring

during the second period’s rapid rise in ozone. The Atascadero ozone exceedance

occurred only for one hour at 1900 PST. In addition, exceedances of the ozone

standard occurred in the adjacent air basins including SFBAAB at Livermore, and

throughout central and southern SJVAB. NCCAB ozone concentrations remained low

except for the inland site at Hollister and the higher elevation site at Pinnacles National

Monument (1100 feet).

An examination of the time of peak ozone concentration throughout central

California on August 28 shows an early evening peak in the northern County, mid to late

afternoon peaks at Hollister and Pinnacles National Monument, and late afternoon

peaks in the Santa Clara Valley. These late peak times indicate impacts from
Technical Support for Assessments F-19

transported emissions. The progression of the hour of peak ozone concentration

extends southward from the southern SFBAAB to Pinnacles then Paso Robles and

Atascadero. This progression suggests that transported emissions from the SFBAAB

impacted the northern County. Within the SJVAB, the early afternoon hour peaks within

the Fresno and Bakersfield urban areas indicate primary impacts from local emissions.

However, the late afternoon peaks to the east and southeast of these urban areas

indicate downwind impacts.

Table F-12

Air Quality Data*

August 26, 1998 August 27, 1998 August 28, 1998

Site Max

Ozone

ppm

Hour

of Max

Max

Ozone

ppm

Hour of

Max

Max

Ozone

ppm

Hour of

Max

San Luis Obispo County

Paso Robles 0.074 1200 0.095 1200 0.114 1900

Atascadero 0.056 1100 0.072 1100 0.097 1900

Black Mountain 0.063 2300 0.085 2300 0.096 1200

San Francisco Bay Area

Livermore 0.054 1600 0.092 1500 0.101 1500

San Jose-4th 0.048 1500 0.070 1400 0.060 1400

San Martin 0.061 1500 0.092 1400 0.082 1600

North Central Coast

Hollister 0.045 1300 0.072 1300 0.086 1500

Pinnacles 0.063 1300 0.077 1700 0.109 1600

San Joaquin Valley

Turlock 0.081 1700 0.095 1600 0.086 1300

Fresno-1st 0.084 1400 0.101 1400 0.110 1300

Clovis 0.092 1400 0.113 1400 0.128 1300

Sequoia NP-Lookout 0.111 1700 0.107 1600 0.119 1600

Sequoia NP-Kaweah 0.098 1700 0.103 1700 0.100 1700

Parlier 0.095 1500 0.120 1600 0.116 1500

Visalia 0.086 1300 0.103 1700 0.109 1600

Hanford 0.076 1600 0.091 1600 0.103 1300

Bakersfield-Golden 0.084 1300 0.096 1300 0.106 1200

Edison 0.113 1400 0.128 1400 0.150 1300

Maricopa 0.089 1600 0.104 1600 0.108 1400

* Ozone Concentrations exceeding the State standard are shaded and bold faced
Technical Support for Assessments F-20

Meteorology

On August 27, 1998, strong high pressure aloft covered the southwestern United

States and was highest over central California. As the high pressure increased from

August 27 to 28, ozone exceedances became more widespread across central

California.

This buildup in high pressure over the central California coastal area brought about a

change in wind patterns from August 27 to August 28. At Paso Robles, surface sea

breeze (west-southwest) winds on August 27 switched to generally northerly on August

28. The northerly winds persisted through August 28, increasing by the hour of the daily

maximum ozone concentration (1900 PST). Atascadero exhibited a similar wind pattern

change from August 27 to 28. Northerly surface winds extended from the Santa Clara

Valley and Pinnacles area, as well as the Salinas River Valley throughout August 28. In

addition, the high pressure kept the seabreeze confined to the coastal area of the

northern County. During the late morning and afternoon hours of August 28, northeast

to east flow was evident in the far western side of the southwestern San Joaquin Valley

at Kettleman and Blackwells Corner. However, there was no evidence of these easterly

winds reaching Paso Robles on August 28.

Surface back trajectories were simulated for this episode. Two-day backward

trajectories from Paso Robles and one-day back trajectories from Pinnacles were

calculated for August 28. The August 28 back trajectory’s path from Paso Robles at

1900 PST originated in the San Jose area during the previous morning, via the

mountainous corridor between the NCCAB and SJVAB. Due to the lack of wind

measurements and the complex elevated terrain along this mountainous corridor, there

is some uncertainty in the back trajectory. However, the back trajectory from Paso

Robles to east of King City (reached early afternoon) is reasonable because of the

existence of wind measurements and flatter terrain. The back trajectory from Pinnacles

indicated that emissions had originated from the SFBAAB earlier in the day via the

Santa Clara Valley. These combined findings suggest that SFBAAB emissions had at

least transported into the Pinnacles area by mid to late afternoon and could have

continued southward to impact the northern County during the early evening.

Central California winds during August 27 and 28 were generally northwest to north

from the surface to approximately 3500 feet and offshore above 3500 feet. Fort Ord

offshore winds (north to northeast) extended to 5,000 feet above a shallow coastal

marine layer on August 28. Black Mountain (3600 feet) in the central County had

persistent and strong offshore east-northeast winds, reaching 22 mph during the

morning hours of August 28. Offshore winds (east to southeast) at Vandenberg AFB

extended approximately to 18,000 feet above a shallow marine layer. Moderate

offshore winds (5 to 15 mph) at Visalia were found between 3900-5100 feet in the

morning hours, but strengthened and extended from 2600 feet through 5100 feet during

the afternoon hours on August 27 and 28.
Technical Support for Assessments F-21

Surface temperatures in southern Monterey County to the central County were the

highest throughout central California on August 28. Peak temperatures at Paso Robles

reached 104 degrees Fahrenheit on August 28. Peak temperatures in the SJVAB

reached 99 and 97 degrees on August 28 at Fresno and Bakersfield, respectively. The

high surface temperatures on August 28 resulted in deep vertical mixing in some areas

of southern Monterey County to the central County. This deep vertical mixing could

have served as a mechanism to further draw air into the area where the exceedances

occurred in the northern County, thus enhancing transport and vertical interchange.

The major findings supporting the staff’s conclusion that the northern County was

impacted by significant emissions from the SFBAAB are listed below:

• high ozone concentrations in the southern SFBAAB;

• low ozone concentrations at the surface in the NCCAB;

• high ozone concentrations in the elevated portions of NCCAB at Pinnacles;

• surface and aloft northwest to north winds within the first few thousand feet;

• mid-afternoon SFBAAB emissions impact on Pinnacles;

• the progression of the time of the southern SFBAAB to the northern County peak

ozone concentration;

• the Paso Robles early evening (1900 PST) ozone concentration peak occurring

with increasing northerly winds; and

• light surface northerly winds at Atascadero.

In addition, the following findings suggest that the northern County was impacted by

significant emissions from the SJVAB:

• high ozone concentrations in the SJVAB;

• offshore flow aloft throughout central California;

• State 1-hour ozone exceedances at Black Mountain; and

• deep vertical mixing over the County and southern NCCAB.

d. “Significant” Transport Impact – May 11, 1996

Air Quality

The maximum ozone concentrations for the days leading up to the exceedances at

Paso Robles and Atascadero on May 11, 1996 are shown in Table F-13. Maximum

ozone concentrations on May 9 were low throughout central California. Paso Robles

and Atascadero maximum ozone concentrations were 0.065 and 0.066 ppm,

respectively. Maximum ozone concentrations increased at Paso Robles and

Atascadero, as well as in the adjacent air basins on May 10. Ozone concentrations

continued to increase on May 11, 1996 when both Paso Robles and Atascadero

exceeded the State ozone standard with 0.097 ppm. The May 11 Paso Robles

exceedances occurred over a three hour period beginning 1200 PST, while Atascadero

exceedances also occurred over a three hour period beginning at 1300 PST. In
Technical Support for Assessments F-22

addition, ozone concentrations exceeding the State ozone standard occurred in all the

adjacent air basins.

An examination of the time of peak ozone concentration throughout central

California on May 11 shows an early afternoon peak in the northern SLOC, mid to late

afternoon peaks at Hollister and Pinnacles National Monument, and late afternoon

peaks in the Santa Clara Valley. These late peak times indicate impacts from

transported emissions.

Table F-13

Air Quality Data*

May 9, 1996 May 10, 1996 May 11, 1996

Site Max

Ozone

ppm

Hour of

Max

Max

Ozone

ppm

Hour of

Max

Max

Ozone

ppm

Hour of

Max

San Luis Obispo County

Paso Robles 0.065 1100 0.081 1500 0.097 1300

Atascadero 0.066 1100 0.083 1500 0.097 1400

Morro Bay 0.041 1200 0.044 1300 0.061 0200

San Luis Obispo 0.040 1300 0.050 1000 0.081 1300

San Francisco Bay Area

San Jose-4th 0.046 1400 0.062 1600 0.110 1500

Gilroy 0.061 1600 0.076 1400 0.115 1700

North Central Coast

King City 0.049 1400 0.065 1200 0.094 1600

Pinnacles 0.064 1500 0.088 1700 0.107 1900

San Joaquin Valley

Tracy 0.063 1400 0.075 1500 0.085 1500

Crows Landing 0.068 1500 0.073 1500 0.080 1400

Turlock 0.072 1600 0.080 1700 0.106 1500

Fresno - First 0.066 1300 0.081 1500 0.089 1500

Clovis 0.070 1300 0.077 1400 0.096 1200

Parlier 0.077 1300 0.093 1500 0.117 1400

Hanford 0.081 1400 0.101 1600 0.108 1300

Visalia 0.065 1700 0.080 1600 0.105 1600

Bakersfield-Golden 0.067 1200 0.082 1300 0.116 1700

Arvin 0.075 1500 0.106 1600 0.120 1700

Maricopa 0.070 1000 0.076 1100 0.104 1400

Santa Barbara County

Gaviota-GTC Site C 0.073 1500 0.082 1400 0.130 1400

Ventura County

Simi Valley 0.067 1300 0.100 1200 0.134 1400

* Ozone Concentrations exceeding the State standard are shaded and bold faced
Technical Support for Assessments F-23

Timing of the 1-hour peak daily ozone concentration from the SFBAAB to Paso

Robles does not suggest a connection (see Table F-13). Moreover, while there were no

ozone exceedances on May 10, on May 11 Gilroy began exceeding the State 1-hour

standard at 1300 PST, Pinnacles National Monument at 1500 PST, Paso Robles at

1200 PST, and Atascadero at 1300 PST. Though not quite reaching a State

exceedance, King City’s daily 1-hour peak ozone concentration reached 0.094 ppm at

1600 PST. Clearly, there is a progressive timing in the first hour of a State exceedance

from Gilroy to Pinnacles National Monument, and subsequently to King City. However,

that progression is not evident beyond King City. The occurrence of the first hour

(1200 PST) and peak hour (13-1400 PST) of the ozone exceedances at Paso Robles

occurs earlier to a progression beyond King City, let alone at Pinnacles National

Monument. Therefore, ozone from the SFBAAB via the Salinas Valley and Pinnacles

National Monument routes did not contribute to the ozone exceedances at Paso Robles

and Atascadero on May 11.

The timing and distribution of the daily maximum ozone concentration on May 10

suggests that the Hanford exceedance was primarily the result of surface emissions

from the Fresno urban plume and not the SFBAAB. The elevated daily maximum ozone

concentrations at Tracy (0.085 ppm) and Crows Landing (0.080 ppm) on May 11

indicate that some SFBAAB emissions impacted northern SJVAB. However, these

concentrations are below the State 1-hour ozone standard. In addition, the timing of the

daily maximum ozone concentration at these two northern SJVAB sites is similar to

Paso Robles and Atascadero, not considerably prior. Therefore, it’s doubtful that

significant SFBAAB emissions via the San Joaquin Valley contributed to the May 11

ozone exceedances at Paso Robles and Atascadero.

Meteorology

On May 10 high pressure aloft was centered along the western U. S. coast. The

center of this high pressure moved eastward into the Great Basin by the late afternoon

of May 11, becoming stronger as it moved over California. As the high pressure over

California increased from May 10 to 11, ozone exceedances became more widespread

across central California.

This increase in high pressure over California brought light to moderate northerly

winds to the northern County on May 10-11. Paso Robles wind speeds were light

throughout May 11. Atascadero winds were light and from the south-southwest during

the nighttime hours of May 10-11, otherwise winds were generally from the north

through northeast.

Surface back trajectories were simulated for this episode. Two-day backward

trajectories from Paso Robles and Atascadero at the hour of the daily maximum ozone

concentration were calculated for May 11. In general, the back trajectories indicated

that the surface northerly flow was very weak. Specifically, the back trajectories

indicated that the path of airflow had spent most of May 11 between the Monterey
Technical Support for Assessments F-24

County line and the Paso Robles and Atascadero areas, while spending the late

afternoon and evening of May 10 in the southeastern portion of Monterey County.

The winds aloft on May 11 were generally offshore at Vandenberg AFB, Fort Ord,

Oakland, and Fresno. The offshore flow was as deep as 5800 feet at Fresno and 5000

feet at Oakland, Fort Ord, and Vandenberg AFB.

Surface temperatures in Paso Robles, Atascadero, and the San Joaquin Valley were

high on May 11. Peak temperatures at Paso Robles and Atascadero reached 95 and

91 degrees Fahrenheit. Peak temperatures at Fresno and Bakersfield were 90 and 88

degrees Fahrenheit, respectively. The high surface temperatures resulted in deep

vertical mixing on May 11 over the County and central and southern SJVAB. This deep

vertical mixing could have served as a mechanism to further draw air into the area

where the exceedances occurred in the northern County, thus enhancing transport and

vertical interchange.

The major findings, supporting the ARB staff's conclusion that the northern County

was impacted from significant surface emissions from within the County and by

significant aloft emissions from the SJVAB are:

• buildup of northern County emissions under light northerly surface winds;

• high ozone concentrations in the Hanford area the day prior, and high ozone

concentrations in the SJVAB on May 11;

• deep vertical mixing in the SJVAB;

• deep layer of offshore winds above 1500-2000 feet at Fresno, Oakland, Fort Ord,

and Vandenberg AFB; and

• deep vertical mixing in the northern County.

e. “Inconsequential” Transport Impact – September 1, 1996

Air Quality

The maximum ozone concentrations for the day leading up to the exceedance at

Atascadero on September 1, 1996 are shown in Table F-14. Maximum ozone

concentrations on August 31 were low in the County, moderate in the NCCAB, and

exceeding the state ozone standard in the southern SFBAAB and in the SJVAB. By

September 1 ozone concentrations increased in the northern County, but decreased in

the air basins adjacent to the County. The Atascadero air monitoring station exceeded

the state 1-hour ozone standard with 0.095 ppm for one hour on September 1. In the

adjacent air basins, 1-hour ozone exceedances were confined to the SJVAB at Turlock,

the Fresno urban area, and the southern San Joaquin Valley south of Oildale. Daily

maximum 1-hour ozone concentrations were less than 0.064 ppm in the NCCAB to the

north and were less than 0.074 ppm in the Santa Barbara County to the south.

Exceedances of the 1-hour national ozone standard were confined to Edison in the

SJVAB on September 1.
Technical Support for Assessments F-25

Table F-14

Air Quality Data*

August 31, 1996 September 1, 1996

Site Max Ozone

ppm

Hour of

Max

Max Ozone

ppm

Hour of

Max

San Luis Obispo County

Paso Robles 0.066 1200 0.084 1700

Atascadero 0.070 1200 0.095 1700

Morro Bay 0.030 1400 0.033 1900

San Luis Obispo 0.053 1500 0.052 1100

North Central Coast

Pinnacles 0.081 1800 0.063 1200

San Francisco Bay Area

King City 0.059 1300 0.056 1200

Gilroy 0.093 1500 0.066 1500

San Joaquin Valley

 Tracy 0.077 1400 0.088 1600

 Turlock 0.074 1600 0.096 1400

Fresno-1st 0.138 1400 0.107 1200

 Clovis 0.130 1400 0.123 1200

 Parlier 0.151 1600 0.093 1300

Hanford 0.144 1400 0.083 1100

 Visalia 0.128 1400 0.082 1300

 Oildale 0.121 1200 0.087 1100

Bakersfield-Golden 0.124 1200 0.096 1100

 Arvin 0.120 1300 0.101 1500

 Edison 0.142 1400 0.129 1300

Maricopa 0.095 1200 0.096 1500

Santa Barbara County

 Santa Maria-Broadway 0.034 1500 0.034 1200

 Los Flores Canyon #1 0.106 1500 0.069 1300

 Paradise Road 0.097 1400 0.075 1500

* Ozone Concentrations exceeding the State standard are shaded and bold faced
Technical Support for Assessments F-26

Elevated concentrations of oxides of nitrogen were measured at Atascadero during

the morning and evening hours of August 31. The local emissions of oxides of nitrogen

were magnified by the addition Labor Day traffic on U. S. Highway 101. Elevated

concentrations of oxides of nitrogen continued overnight and into the morning hours of

September 1.

Meteorology

On August 31 high pressure was centered over the California’s central coast and

desert interior, causing the buildup of ozone concentrations in the central and southern

portions of California. However, by September 1 lower pressure aloft resulted in

decreased ozone concentrations over portions of central and southern California except

for the northern County.

The nighttime and morning surface winds at Atascadero were calm on August 31

and September 1. Afternoon west-southwest seabreeze winds were light on August 31

and September 1. A one-day surface backward trajectory from Atascadero was

calculated for September 1, 1996. The back trajectory indicated that air arriving in

Atascadero at the time of the peak ozone concentration (1700 PST) had originated off

the coast earlier in the day. The winds aloft at Vandenberg AFB, Oakland, and Fresno

were generally onshore both on August 31 and September 1.

The major findings, supporting the ARB staff's conclusion that SLOC was

predominately impacted by emissions from within the SLOC are:

• weak onshore surface airflow in the northern SLOC;

• onshore flow aloft at Oakland, Vandenberg AFB, and Fresno;

• abundant SLOC Labor Day ozone precursor emissions;

• geographically isolated Atascadero ozone exceedance; and

• westward back trajectory.