## Background PM 2.5 

## Analysis for the Eastern Gulf of Mexico Outer Continental Shelf

Prepared by: ENVIRON International Corporation Lynnwood

, Washington Baton Rouge, Louisiana

Date: April 2013Contents i ENVIRON 

# Contents

Page

1 Introduction 2

2 Background 2

3 Meteorological Conditions in the EGOM 3

4 Air Monitoring Sites 4

4.1 PM 2.5 Design Values 5

4.2 Trends 7

4.3 Monitoring Dat a Conclusions Regarding PM 2.5 SILs and SMC 8

5 PM 2.5 Precursors and Chemical Transformations 9

5.1 Summary 10

List of Figures

Figure 1: Windrose Plots from Various ASOS Stations and Buoys, with Active Lease Blocks Figure 2: PM2.5 Background Assessment Sites Figure 3: 2000

- 2011 EPA Design Value Trend for 24

- Hour PM 2.5 Figure 4: 2000

- 2011 EP A Design Value Trend for Annual PM 2.5 Figure 5: SEARCH Monitor Locations [Blanchard 2013b]

List of Tables

Table 1: EPA Recommended Approaches for Assessing Primary and Secondary PM2.5 Impacts by Assessment Case
Table 2: EPA Reported Design Values and Averages
Table 3: IMPROVE ConcentrationsBackground PM 2.5 Analysis, EGOM 2 ENVIRON 

# 1 Introduction

Air emission sources complying with the federal Prevention of Significant Deterioration (PSD)
rules are required t o assess the influence of not only primary particulate matter less than 2.5 micrometers in aerodynamic diameter (PM 2.5 

### ), but also impacts of potential formation of secondary PM 2.5



### .

Precursors of PM 2.5 

### include nitrogen oxides (NOx), sulfur oxides (SOx), an d volatile organic compounds (VOCs). These precursors, under specific atmospheric conditions and in the presence of other chemicals integral to the photochemical processes that form secondary
PM 2.5 

### , may coagulate on existing particles or nucleate into new particles. Understanding the state of atmospheric conditions and chemical composition near a PSD source is essential to assessing the influence that the PSD source could have on secondary PM 2.5 

### formation.

The U.S. Environmental Protection Agency (USEPA) has provided draft guidance that allows for a qualitative assessment of secondary PM 2.5 

### formation for PSD sources. The intent is for the assessment to provide sufficient qualitative evidence that the potential for the formation of secondary PM 2.5 

### would not result in overall PM 2.5 

### levels that exceed the NAAQS, and that ultimately a quantitative assessment will not be required to evaluate the formation of secondary
PM 2.5



### .
This memo has been prepared in response to the USEPA draft guidance regarding secondary
PM 2.5 

### formation. Included is a review of atmospheric conditions and chemical composition within the Eastern Gulf of Mexico (EGOM) Outer Continental Shelf (OCS) region, which may be used to qualitatively predict the potential impact of precursors on the s econdary formation of
PM 2.5



### .

This memo also addresses the use of the PM 2.5 

### Significant Impact Levels (SILs) and significant Monitoring Concentration (SMC), which were vacated by the United States Court of Appeals for the District of Columbia Circuit on Jan uary 22, 2013

.
This memo is targeted at oil exploration activities requiring PSD permits in the EGOM OCS.



# 2 Background

On March 4, 2013, the USEPA issued draft guidance 1 

### for PM 2.5 

### air quality impact assessments under the auspices of the federal PSD rules (Section 165(a)(3) of the Clean Air Act (CAA) and 40 CFR sections 51.166(k) and 52.21(k)).

The USEPA PM 2.5 

### guidance provides a summary of required information to support the quantitative assessment of secondary formation of PM 2.5 

### . This guidance del ineates four (4) possible scenarios where quantitative impact assessments will ultimately be required . Each
scenario is associated with direct emissions of PM 2.5 

### and of secondary precursors (i.e., NO
x 

### and SO 2 

### ) in relation to the ir Significant Emission Rates (SER). Table 1 describes the various USEPA assessment recommendations as a function of the pollutant emissions.

1 Available at http://www.epa.gov/ttn/scram/guidance/guide/Draft_Guidance_for_PM25_Permit_Modeling.pdfBackground PM 2.5 Analysis, EGOM 3 ENVIRON Table 1 : EPA Recommended App roaches for Assessing Primary and Secondary PM2.5 Impacts by Assessment Case

Assessment Case Description of Assessment Case Direct PM 2.5 Impact Approach Secondary PM 2.5 Impact Approach
Case 1: No Air Quality Analysis Direct PM 2.5 emissions < 10 tpy NOx and SO 2 emissions < 40 tpy Not Applicable Not Applicable

Case 2: Primary Air Quality Impacts Only Direct PM 2.5 emissions > 10 tpy NOx and SO 2 emissions < 40 tpy Appendix W preferred or approved alternative dispersion model Not Applicable

Case 3: Primary and Secondary Air Quality Impacts Direct PM 2.5 emissions > 10 tpy NOx and/or SO 2 emissions > 40 tpy Appendix W preferred or approved alternative dispersion model • Qualitative • Hybrid qualitative / quantitative • Full quantitative photochemical grid modeling
Case 4: Secondary Air Quality Impacts Only Direct PM 2.5 emissions < 10 tpy NOx and/or SO 2 emissions > 40 tpy Not Applicable • Qualitative • Hybrid qualitative / quantitative • Full quantitative photochemical grid modeling



### Note that although the PM 2.5 

### guidance contains four cases, there are only two cases for primary
PM 2.5 

### (either less than or greater than the SER) and two cases for secondary PM 2.5 

### (either less than or greater than the NOx/SO 2 

### SER). Note al so that the approach for addressing secondary
PM 2.5 

### is independent of how primary PM 2.5 

### is addressed. If NOx/SO 2 

### emissions are greater than their SER, a qualitative (or quantitative) approach to secondary PM 2.5 

### is required, regardless of whether primary PM 2.5 

### is greater than its SER or not.

The PM 2.5 

### guidance also addresses how to use ambient monitoring data to (a) show that the
PM 2.5 

### SILs may still be applied as a screening tool, and (b) demonstrate compliance with the preconstruction monitoring require ments [Section 51.166(m) or 52.21(m)].



# 3 Meteorological Conditions in the EGOM

Windrose plots for a range of ASOS stations and environmental buoys in the Gulf of Mexico are

shown in Figure 1 . These data were extracted from the NCDC’s TD

- 3505 dataset . Also shown are the active lease blocks in the GOM, and the line dividing the EGOM from the Western GOM.

The generally stronger wind speed conditions found at sea can be seen, with more winds in excess of 10 m/s over the water. Near the South of the plot, the winds blow more often from the East or ESE. Closer to shore, the winds become more evenly distribut ed, though there is still a tendency for winds to blow from the East to Southeast. The land

- sea breeze effect can clearly

be seen in the on

- shore windroses, which have a tendency to be aligned with winds perpendicular to the shoreline. However, most site s still exhibit a wide range of wind directions, consistent with weak topographic forcing.Background PM 2.5 Analysis, EGOM 4 ENVIRON Figure 1

. Windrose Plots from Various ASOS Stations and B uoys , with Active Lease Blocks



### Emissions of PM 2.5 

### precursors from lease blocks in the EGOM would , according to the

windroses from buoys located between the majority of EGOM lease blocks and shore , be nearly equally likely to be blown in any direction, with a slight preference for blowing toward the

Louis iana shore.



# 4 Air Monitoring Sites

Currently, there are only a handful of PSD permits and pending applications for sources in the EGOM. There are no environmental monitors in the vicinity of the existing lease blocks where oil exploration activities might take place. The PM 2.5 

### concentration in the OCS is expected to be lower than the concentration on shore, due to the scarcity of sources in the EGOM, and the
abundance of sources of PM 2.5 

### on land (vehicles, industry, etc.). Using shore

- based monitors is

t herefore conservative, in that it over

- estimates the existing PM 2.5 

### concentrations in the EGOM.

PM 2.5 

### design values and trends were reviewed for sites bordering the Eastern Gulf of Mexico. The USEPA Air Quality System (AQS) federal reference monitors (FRM) and Interagency Monitoring of Protected Visual Environments (IMPROVE) monitors, selected as representative samples for the Eastern Gulf region, are depicted in Figure 2

.Background PM 2.5 Analysis, EGOM 5 ENVIRON 

### 4.1 PM 2.5 

### Design Values
The USEPA publishes design values for all AQS monitors, which are used for determination of attainment with air quality standards. The 24

- hour design values are defined as 3 year average
98 th 

### percentile 24

- hour PM 2.5 

### concentrations, while the annual design values are the simple 3

- year average PM 2.5 

### concentrations. The most recent design values for the sites shown as red
diamonds in Figure 2 are provided in Table 2

.

As illustrated in Figure 2 by the yellow circles, there are three (3) IMPROVE monitors in the EGOM region, located “near” or in the Class I areas. The 98 th 

### percentile 24

- hr concentrations for each year (and the three

- year average) for these sites are reported in Table 3 , for the years 2009 through 2011. These data were reviewed to ensure Class I areas are below the design values provided by the USEPA AQS monitors.

Figure 2

. PM2.5 Background Assessment SitesBackground PM 2.5 Analysis, EGOM 6 ENVIRON Table 2 : EPA Reported Design Values and Averages

EPA Design Values (DV) of PM 2.5 for 2009

- 2011 (ug/m 3 )

Site Site Code 24

- Hr DV Annual DV
Fairhope, AL 01

- 003

- 0010 21 9.7 Chickasaw, AL 01

- 097

- 0003 19 9.8 Theordore, AL 01

- 097

- 2005 20 9.2 Gainesville, FL 12

- 001

- 0023 20 7.7 Gainesville, FL 12

- 001

- 0024 20 7.5 Panama City, FL 12

- 005

- 1004 21 8.9 Crystal River, FL 12

- 017

- 0005 16 7.3
Ferry Pass, FL 12

- 033

- 0004 20 9
Tampa, FL 12

- 057

- 0030 16 9 Valrico, FL 12

- 057

- 3002 17 7.8 Tallahassee, FL 12

- 073

- 0012 25 9.9 St. Petersburg, FL 12

- 103

- 0018 16 7.7 Clearwater, FL 12

- 103

- 1009 15 7.4
Sarasota, FL 12

- 115

- 0013 15 6.8 Valdosta, GA 13

- 185

- 0003 28 10.4 Waveland, MS 28

- 045

- 0003 21 9.8 Gulfport, MS 28

- 047

- 0008 18 9.6 Pascagoula, MS 28

- 059

- 0006 21 9.5
Average 19.39 8.72

Minimum 15 6.8

Maximum 28 10.4

NAAQS 35 12

Table 3 : IMPROVE Concentrations

IMPROVE Design Values (DV) of PM 2.5 (ug/m 3 )

Site Site

Code 24

- Hr

DV Annual

DV

Breton Island BRIS1 17.50 8.30

Chassahowitzka CHAS1 14.36 7.13

St. Marks SAMA1 17.81 7.73

Average 16.56 7.72Background PM 2.5 Analysis, EGOM 7 ENVIRON 

### 4.2 Trends

The 3

- year monitoring design values for the AQS and IMPROVE sites illustrated in Figure 2
were reviewed from 2000

- 2011 to establish a regional trend.

Figure 3 illustrates the average 24

- hour PM 2 .5 

### 3

- Year design value trends, the average design value plus the significant impact level (SIL) for 24

- hour PM 2.5 

### (1.2 μg/m 3 

### ), the 2007 NAAQS for

24

- hour PM 2.5 

### ( 35 μg/m 3 

### ), and the gap between the design value plus SIL to the NAAQS. The

trend shows an overa ll improvement in PM 2.5 

### since the 3

- year period ending in 2006. These

decreases in PM 2.5 

### design values may be a function of improved control technologies and the introduction of new regulatory measures.

Figure 4 illustrates the average annual PM 2.5 

### design value trends, the average design value plus the significant impact level (SIL) for annual PM 2.5 

### (0.3 μg/m 3 

### ), the 2013 NAAQS for annual

PM 2.5 

### ( 12 μg/m 3 

### ), and the gap between the design value plus SIL to the NAAQS. The trend shows an overall improvement in PM 2.5 

### since the 3

- year period ending in 2006 . These

decreases in PM 2.5 

### design values may be a function of improved control technologies and the
introduction of new r egulatory measures.

Figure 3 . 2000

- 2011 EPA Design Value Trend for 24

- Hour PM 2.5Background PM 2.5 Analysis, EGOM 8 ENVIRON 

### In the context of sources of PM 2.5 

### , the growing gap between DV+SIL (the design value plus the SIL) and the NAAQS corresponds with a decreased like lihood of needing to perform a quantitative NAAQS analysis.

Figure 4 : 2000

- 2011 EP A Design Value Trend for Annual PM 2.5



### 4.3 Monitoring Data Conclusions Regarding PM 2.5 

### SILs and SMC
Because the monitoring sites shown in Figure 2 are representative (or conservative) of the EGOM OCS region, the data shown in Tables 2 and 3 may be used in place of on

- site pre

construction monitoring to satisfy 40 CFR 51.166(m) and 52.21(m) of the EPA’s regulation.

The PM 2.5 

### 24

- hour NAAQS value is 35 μg/m 3 

### , and the Class II SIL is 1.2 μg/m 3 

### . The annual NAAQS value is 12 μg/m 3 

### , and the Class II SIL is 0.3 μg/m 3



### .

Because the maximum 24

- hour design value shown in Tables 2 and 3 is less than 33.8 μg/m 3 

### (the NAAQS minus the SIL), the 24

- hour PM 2.5 

### Class II SILs is sufficiently protective of the NAAQS, and may be used as a screening tool when modeling direct emissions of PM 2.5



### .
Similarly, because the maximum annual design value shown in Tab les 2 and 3 is less than
11.7 μg/m 3 

### (the NAAQS minus the SIL), th e use of the annual PM 2.5 

### Class II SIL is sufficiently protective of the NAAQS and may be used as a screening tool when modeling direct emissions of PM 2.5



### .Background PM 2.5 Analysis, EGOM 9 ENVIRON 

### The Class I PM 2.5 

### SILs were vacated/remanded along with the Class II SILs by the DC District Court . Class I SILs are normally used as a screening tool to assess whether a full Class I Increment analysis is required, and if so, whether a project significantly contributes to Increment consumption. The PM 2.5 

### Increments became effective relatively recent ly (October 20, 2011), and only a few PSD projects have been proposed in the EGOM since the major source baseline
date . Emissions from PSD projects outside of the EGOM would not affect a Class I area at the same time as emissions originating from the EGOM , due to the very different meteorological conditions. When the wind blows from the EGOM toward a Class I area, it blows emissions
from land

- based sources further in

- land, away from the relevant Class I areas. Therefore, the Class I SILs may still be tre ated as a “target value,” below which it is unlikely the PM2.5 Class I
Increments will be consumed.



# 5 PM 2.5 

# Precursors and Chemical Transformations

Sources within the EGOM contribute to increases in particulate concentrations through direct emission of par ticulates and emission of particulate precursors. As indicated in the Draft PM 2.5 

### Guidance, precursors can be addressed either by a qualitative assessment of the state of atmospheric chemistry for a region, or by use of photochemical modeling. However, if a qualitative assessment provides ample evidence that precursors will not cause primary and secondary PM 2.5 

### emissions to exceed or approach the NAAQS, then the application of photochemical models may not be required.

Investigations of the Southeastern Aer osol Research and Characterization (SEARCH) monitoring network [Blanchard 2013a, Blanchard 2013b] have provided detailed information on the trends and speciation of the regional pollutants. The SEARCH network encompasses the eastern Gulf of Mexico and has operated since mid

- 1998 assessing numerous pollutants relevant to the development of secondary PM 2.5 

### . The SEARCH network includes monitoring
locations at the sites illustrated in Figure 5

.
Recently published studies of the SEARCH ne twork have shown that concentrations of PM 2.5 

### have trended downward from 1999

– 2010. Secondary formation of PM 2.5 

### is due largely to reactions of SO 2 

### and NO
x 

### with NH 3 

### in the atmosphere, resulting in increased particle composition of sulfate and nitrate respectively , a notion supported by the SEARCH network analyses. Over the SEARCH network sampling period, the mean annual sulfate and nitrate concentrations had ranges o f 3.2

– 4.3 μg/m3 and 0.3

– 0.9 μg/m 3 

### respectively, indicating a prominence of sulfate.

Blanchard et al. [2013b] indicated that particulate sulfate concentrations decreased in tandem with decreases in SO 2 

### emissions reported by electrical generating units. A one

- to

- one relationship was not observed, likely due to the exclusion of other sources emitting SO 2



### . Decreases in SO 2 

### emissions and SO 4 

### concentrations were also observed within the larger Clean Air Status and Trends Network (CASTNet) indicating a robust geographic range in the regional downward trend of sulfate. However, a reduction in the conversion of SO 2 

### to sulfate potentially increases the availability of ammonia for the conversion of NO
x 

### to nitrate.

The formation of particulate nitrate is a functi on of NO
x 

### , NH 3 

### , and SO 4 

### interactions as well as atmospheric conditions such as temperature and humidity, thus causing additional complexity in understanding the relationships associated with particulate formation. The use of thermal equilibrium models [Bla nchard 2007] indicate that, within the SEARCH network, the formation of nitrate is limited by the abundance of NH 3 

### , a compound which showed no significant trend. However, nitrate concentrations did not increase with decreasing sulfate concentrations,Background PM 2.5 Analysis, EGOM 10 ENVIRON 

### sugge sting that, despite reductions in SO 2 

### emissions, the reaction of SO 2 

### with NH 3 

### dominates the region. This notion is further validated by the correlation of decreasing sulfate particulates and ammonium particulate concentrations within the SEARCH network. Th erefore, the addition of a new source of NO
x 

### would likely have little impact on the formation of secondary nitrate within the region.

Figure 5

. SEARCH Monitor Locations [Blanchard 2013b]



### 5.1 Summary
A significant increase in PM 2.5 

### concentrations near the eastern Gulf of Mexico from a source of nitrogen oxides is unlikely. The region is dominated by the conversion of sulfur oxides to sulfate by reactions with ammonia. Analysis of the SEARCH network has shown that as sulfate

concentr ations and sulfur oxide emissions have declined, there has been no reciprocal increase in nitrate, suggesting that the sulfur oxide and ammonia reaction remains dominant. Further, assessment of the EPA FRM monitors shows a declining trend in PM 2.5 

### . The mos t recent design values allow for an increase of combined primary and secondary PM 2.5 

### of 14.41 μg/m 3 

### before
the 24

- hour NAAQS level is met

.Background PM 2.5 Analysis, EGOM 11 ENVIRON 

# References

Blanchard, C. L., Tanenbaum, S., & Hidy, G. M. (2007). Effects of Sulfur Dioxide and Oxides of Nitrogen Emission Reductions on Fine Particulate Matter Mass Concentrations: Regional Comparisons. Journal of the Air & Waste Management Association

, 57 (11), 1337

– 1350.
doi:10.3155/1047

- 3289.57.11.1337

Blanchard, C. L., Hidy, G. M., Tanenbaum, S., Edgerton, E. S., & Hartsell, B. E. (2013a). The Southeastern Aerosol Research and Characterization (SEARCH) study: Spatial variations and chemical climatology, 1999

– 2010. Journal of the Air & Waste Management
Association

, 6 3 (3), 260

– 275. doi:10.1080/10962247.2012.749816

Blanchard, C. L., Hidy, G. M., Tanenbaum, S., Edgerton, E. S., & Hartsell, B. E. (2013b). The Southeastern Aerosol Research and Characterization (SEARCH) study: Temporal trends in gas and PM concentrations an d composition, 1999

– 2010. Journal of the Air & Waste Management Association

, 63 (3), 247

– 259. doi:10.1080/10962247.2012.748523