2008 PM2.5 Plan 

## Appendix E

District Additions to the Conceptual Model2008 PM2.5 Plan This page intentionally blank.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-1 

## Appendix E District Additions to the Conceptual Model

This Appendix provides supplemental discu ssion of key meteorological, atmospheric
and emission issues that affect PM2.5 c oncentrations. EPA recommends starting the PM2.5 SIP analysis by establishing a c onceptual description expressing the factors involved in creating the PM2. 5 concentrations found in the nonattainment area. A full conceptual description must include:

• The natural processes of climate and meteorology that cause PM2.5 to
accumulate and form additional PM2.5 from precursors

• Atmospheric factors that caus e PM2.5 to form or be removed

• Emissions patterns and events that require special consideration The SJV PM2.5 SIP Modeling Pr otocol discusses many of t he technical issues involved in the conceptual model of PM2.5 for the Valley and references a conceptual model document that was developed from resear ch conducted for the CRPAQS/IMS 95 study to explain the dynamics of both PM10 and PM2.5 events. The discussion in this Appendix was develo ped by the District to further ex plain key factors associated with PM2.5 in the San Joaquin Valley that are not fully addressed by the Protocol or the referenced conceptual model document. A va riety of special subjects have been assessed by the District to provide a co mprehensive review of technical issues
associated with PM2.5 concent rations that occur in the Valley. This discussion completes the District conceptual description of PM2.5 as a technical foundation for the
PM2.5 SIP.

In addition to use in the development of the SIP, elements of the comprehensive conceptual description are in use on a daily basis to support air quality forecasting. Understanding conditions asso ciated with increases in PM2. 5 concentrations provides opportunity to alert the public to condition s that may result in poor air quality and supports decision making for smoke managem ent and residential burning curtailments to prevent air quality deterioration.

CONTENTS 1. Climate and Meteorology
a. Seasonal Differences b. Meteorological Influences on PM2.5 Concentrations c. Significant Changes in AQI Due to Meteorological Events 2. Physical and Chemical Processes a. PM2.5 Formation and Removal During Fog Episodes b. Dry Deposition
c. Nitrate Events
3. Emissions Related Issues a. Day of Week and Holiday Effect
b. Wildfires c. Agricultural and Prescribed Burn Management d. Residential Wood Burning Program

e. Recent ResearchSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-2 1. Climate and Meteorology

The San Joaquin Valley Air Pollution District (District) analyzed meteorological and air quality data in support of t he 2008 PM2.5 Plan. PM2.5 dat a have been collected since 1999. Currently, there are 11 Federal Re ference Method (FRM) PM2.5 air-monitoring sites in the San Joaquin Valley, with at leas t one monitor in each coun ty except Madera.
The cities of Bakersfield and Fresno/Clovis have three sites each due to federal requirements related to their large populations.

1.a Seasonal Differences

PM2.5 is a seasonal pollutant that tends to peak during the fall and winter (late September into February - when nitrat e and seasonal carbon sources dominate) compared to the spring and summer when PM2.5 tends to be lower (March into early September with mostly geologic soil and ro ad material, elemental carbon and some secondary carbon aerosol). The 1999 and 2006 PM2.5 measurements from the Fresno
1 st Street monitoring site are illustrated in Fi gure 1. Historically, PM2.5 levels were higher in 1999 compared to 2006. In 1999, the Fresno-1 st site experienced several days above the NAAQS, whereas in 2006, only one day was above the 65-microgram
standard.

Figure 1 PM2.5 Federal Referen ce Method (FRM) Measurements for
Fresno-1 st for 1999 and 2006 The 65 microgram 24-hour average NAAQS is shown on the chart

0 20 40 60 80 100 120 1401/11/151/292/122/263/123/264/94/235/75/216/46/187/27/167/308/138/279/109/2410/810/2211/511/1912/312/1712/31Fresno 1stPM2.5(μg/m3) 2006

1999

National Ambient Air Quality Standard of 65 μ g / m3San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-3 1.b Meteorological Influen ces on PM2.5 Concentrations

The PM2.5 concentration can be influenced by a va riety of meteorological factors. The District has identified and evaluated several par ameters that merit s pecial attention in discussion of the conceptual description of PM2. 5 in the Valley: rainfall effects, low wind speed stagnation, reduced mixing height invers ion layers, 850mb stability (a regional temperature profile surrogate) and multi-day episode stability. A final review of the 850mb stability parameter shows that the PM2.5 level associat ed with this parameter is declining as Valley emissions are reduced.

1.b.1 Rainfall Effects

In the warm air mass ahead of an approaching cold front, concentrations of fine particulate can significantly increase during periods of light rainfall . Particulate can increase or stay at high levels until t he new air mass arrives following the surface frontal passage. During the Bakersfield precipitation event on February 10 and 11, 2005, PM2.5 nearly doubled during a nine-hour period of light rainfall, as shown in Table 1 and Figure 2. As shown in the weat her maps provided in Figures 3 and 4, the rain was falling during prefrontal conditions.

Table 1 PM 2.5 Data from Bakersfield - Cali fornia Monitoring Station and
Weather Data from Bakersf ield - Meadows Airport
Date Hour PM2.5 ( μ g/m 3 ) Weather Temp (deg F) RH (%) WD WS (mph)

10 Feb 05 20 38 Haze 53 80 CALM CALM 10 Feb 05 21 37 Fog 52 86 S 5 10 Feb 05 22 40 Fog 53 86 ESE 3 10 Feb 05 23 44 Light Rain/Fog 51 89 NNW 3 11 Feb 05 0 51 Fog 52 89 NNE 3 11 Feb 05 1 54 Light Rain 51 92 W 3 11 Feb 05 2 65 Light Rain 52 86 N 7 11 Feb 05 3 70 Light Rain 53 83 N 3 11 Feb 05 4 58 Light Rain 52 89 N 5 11 Feb 05 5 54 Light Rain 50 94 WNW 7 11 Feb 05 6 52 Light Rain/Fog 50 94 WNW 6 11 Feb 05 7 75 Light Rain/Fog 50 94 WNW 5 11 Feb 05 8 75 Light Rain/Haze 53 83 N 8

11 Feb 05 9 70 Haze 54 80 N 9
11 Feb 05 10 68 Haze 58 75 N 12
11 Feb 05 11 51 Haze 59 67 NNW 9
Temp = Temperature, RH = Relative Humi dity, WD = Wind Direction, WS = Wind SpeedSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-4 Figure 2 PM2.5 During Rain Event in Bakersfield, February 10th and 11 th , 2005 Darker shaded bars indicate preci pitation reported during the hour

PM2.5 DURING RAIN EVENT

0 10 20 30 40 50 60 70 80

20 21 22 23 0 1 2 3 4 5 6 7 8 9 10 11

HOURPM2.5 (μg/m3)

Figure 3 Surface weather map for 4 PM PST (Hour 16) on February 10, 2005 Shading indicates light precipitationSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-5 Figure 4 Surface weather map for 4 AM PST (Hour 4) on February 11, 2005 Purple shading indicates light precipitation

1.b.2 Wind Speed

Stagnant conditions can lead to a buildup of emissions near the emission source area, producing a gradual increase in pollutant concentrations. The longer the stagnant period lasts, the higher the particulate concentrations can rise. An
increase in winds causes an end to t he stagnant conditions and can transport the polluted air mass downwind, resulting in a lo wering of particulate concentrations in the emission source area. Figure 5 illustra tes that during stagnant (low wind speed conditions), PM2.5 levels can be high. Duri ng the early morning hours of February 14, 2006, winds were less than 3 MPH, resulting in poor dispersion conditions and elevated PM2.5 readings (generally above 50 μ g/m 3 ). After 10 PST, the winds gradually
increased and the PM2.5 levels decreased. This plot shows the response of particulates to changes in wind speed.

1.b.3 Mixing Height and Inversion Layers

Vertical mixing height is the elevation in the atmosphere into which emissions will freely mix and disperse. In Figure 6, t he base of the inversion layer is equivalent to the mixing height. Vertical mixing is reduced when an inve rsion layer or temperature inversion is present. A temperature inversion is a deviati on from the typical tem perature profile in aSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-6 well-mixed atmosphere, where temperat ure decreases with height. Temperature decreases with height in the layer defi ned by the mixing depth in Figure 6.

Figure 5 Plot of real-t ime PM2.5 measurements ( μ g/m 3 ) and wind speed (mph) at Fresno-1 st on February 14, 2006

0 10 20 30 40 50 60 70 80

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

HourReal-time (BAM) PM2.5μg / m3

0 2 4 6 8 10 12 14 16Wind Speed (MPH) Real-time (BAM) PM2.5

Wind Speed (MPH)

Figure 6 Temperature sounding plot with an inversion layer presentSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-7 Typically, an inversion is a layer of air warme r than the layer below it as shown in Figure 6. The warmer layer aloft prevents the us ual rising airflow that disperses emissions from the ground because the c ooler air below the inversion layer does not rise through the warmer air above. As shown in Figure 6, air contaminants accumulate near the ground as emissions continue to be released in to the cooler layer near the surface. Temperature inversions play a crucial ro le in trapping PM2.5 near the San Joaquin Valley’s surface. An example of a temperature inversion is from an aircraft measurement from Fresno on October 24, 2007 in Figure 7. The inversion strength was 19 degrees Fahrenheit from the surface up to 1,000 feet. Figure 7 is an example of a
surface based inversion. A surface based inve rsion is a temperature inversion with the
base at the earth’s surface.

Figure 7 Aircraft temperature measure ment from Fresno on October 24, 2007

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

50 55 60 65 70 75 80

Temperature (Degrees Fahrenheit)Feet (Above Ground Level)

Inversion is from the surface up to 1,000 feet. Strength is 19 degrees Fahrenheit.

Statistical analysis has shown that the 850 MB Stability Parameter correlates with PM levels and is an indicator of how much disp ersion is occurring in the atmosphere. The District defines the 850 MB Stability Para meter as the inversion located between approximately 5,000 feet (850 MB ) and the surface. The 850 MB stability parameter is calculated by taking the 12 Z (4:00 Pacific Local Time) 850 MB temperature at Oakland and subtracting the minimum surface temper ature at Fresno (T850 MB (Oakland) – TMIN (Fresno)). A positive stability param eter indicates warmer temperatures with height. A negative stability parameter shows c ooler temperatures with height. Figure 8
shows the Fresno-1 st 850 MB stability parameter and PM 2.5 plot for 2006. PM2.5 is depicted as the solid line, and the stabilit y parameter is show n as the dots at temperature of 75. Figure 8 shows that during periods of strong stability, PM2.5 tends to climb or remain high. A stable atmos phere would be characterized as any positive temperature difference in degr ees Fahrenheit. The graph al so shows the seasonality of PM2.5 in that during the summer when stabili ty is strong, PM2.5 is low. PM2.5San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-8 formation in the atmosphere tends to be more pronounced during the fall and winter months compared to the summer.

Figure 8 Graph showing the Fresno-1 st stability parameter and Federal Reference Method (FRM) PM2.5 measurements for 2006

PM2.5 tends to follow the atmospheric disper sion conditions of the San Joaquin Valley. During multiple days of a stable atmosphere, local emissions accumulate under poor dispersion conditions resulting in accumu lating PM2.5 concentrations. Preliminary analysis of comparable st rength meteorology in 1999 / 2000 and 2005 / 2006 shows that the stronger stabilit y meteorology in recent years is not resulting in the same high levels of PM as in the past. This may be an indicator that District control measures are contributing to the lower levels of PM in the present.

Table 2 illustrates that PM2.5 fluctuates according to local emissions and meteorology. Strong high pressure built ov er the region on February 5, 2006 trapping PM2.5 near the
surface. PM2.5 levels continued to climb under stagnant dispersion conditions until on February 13 when the Fresno-1 st monitor recorded 71 μ g/m 3

.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-9 Table 2: Federal Reference Method (FRM) PM2.5 ( μ g/m 3 ) Measurements
at Fresno-1 st Monitoring Site



### Date PM2.5 Measurement

2/4/2006 22

2/5/2006 26

2/6/2006 30

2/7/2006 26

2/8/2006 38

2/9/2006 49

2/10/2006 56

2/11/2006 51

2/12/2006 56

2/13/2006 71

2/14/2006 34

2/15/2006 8

PM2.5 and the 850 MB stabilit y parameter were analyzed from 1999 to 2006 during the peak season (November 10 through Januar y 15), Figure 9. This analysis was conducted to determine if meteorology or Dist rict control measures played a role in the current years’ (2005 / 2006) PM2. 5 levels. In Figure 9, st ability increases from left to right, whereas PM increases from bottom to the top. In 1999 and 2000, high stability days tended to result in elevated PM2.5 levels well above the NAAQS. Recently in 2005 and 2006, high stability days resulted in lowe r levels of PM2.5, typically near or below the NAAQS.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-10 Figure 9 PM2.5 measurements at Fresno-1 st related to Oakland 850 MB –Fresno temperature stability parameter. High st ability days (850 MB stability parameter is greater than 0) resulted in high PM2.5 measurements fr om 1999 through 2001. Comparable high stability days since 2003 have not caused high PM2.5
measurements.

1.c Significant Changes in AQI Due to Meteorological Events

Very large changes in the Air Quality Index (AQI) and PM2.5 concentration can occur over a short time period during the PM2.5 s eason. Figure 10 presents a plot of the AQI in Tulare County (Visalia) during the 2005-20 06 PM2.5 season. An AQI improvement of
134 occurred from the 25th to the 26th of November 2005. Stagnant conditions were in place over the San Joaquin Valley Air Basi n on the morning of November 25, 2005 as shown in the Figure 11 weather maps. A vi gorous weather front passed over the region during the afternoon and evening of Novem ber 25. PM2.5 concentration decreased rapidly under the influence of a new cl ean air mass and moderate NW winds. The tightly packed isobars on the weather maps are an indication of a strong pressure gradient and the wind flags indicate moderat e winds. The Visalia PM2.5 concentration decreased rapidly around midnight as show n in Table 3 and Figure 12. Figure 12 displays how the decrease in the PM2.5 c oncentration progresses from northwest to southeast in the San Joaquin Valley Air Basin, coinciding with the front's progression from northwest to southeast across the Valley . The decrease in PM2.5 first occurred in Stockton in the north valley. South Valley st ations at Corcoran and Visalia recorded the decrease in PM2.5 later in the day.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-11 Figure 10 AQI in Tul are County (Visalia) During the 2005-2006 PM 2.5 Season

0 50 100 150 20011/1/200511/8/200511/15/200511/22/200511/29/200512/6/200512/13/200512/20/200512/27/20051/3/20061/10/20061/17/20061/24/20061/31/20062/7/20062/14/20062/21/20062/28/2006

DATEAQI AQI decrease of 134 due to frontal passage, air mass change & moderate NW winds

Table 3 PM2.5 concentration in Visalia, November 25th and 26 th , 2005
Date / Hour Visalia PM2.5 ( μ g/m3) Visalia Municipal Airport Wind Direction and Speed (mph)

25 November 2005 Hour 13 89 ESE 9

25 November 2005 Hour 14 91 NE 6
25 November 2005 Hour 15 85 N 5
25 November 2005 Hour 16 68 N 5

25 November 2005 Hour 17 72 N 3
25 November 2005 Hour 18 78 WNW 10
25 November 2005 Hour 19 88 WNW 12

25 November 2005 Hour 20 79 NW 10
25 November 2005 Hour 21 76 NNE 5
25 November 2005 Hour 22 63 NNW 9

25 November 2005 Hour 23 39 NNW 10
26 November 2005 Hour 0 27 NW 10
26 November 2005 Hour 1 22 NNW 14

26 November 2005 Hour 2 11 NNW 7
26 November 2005 Hour 3 6 NW 8
26 November 2005 Hour 4 2 WNW 5

26 November 2005 Hour 5 3 NW 7San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-12 Figure 11 Surface Weather Maps for 4 AM (12Z), November 25th and 26 th

, 2005San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-13 Figure 12 PM2.5 Concentrat ion, November 25th and 26 th , 2005

0 50 10010:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:000:001:002:003:004:005:006:007:008:009:00

25-

Nov05 25-

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Nov05 26-

Nov05 26-

Nov05

DATE AND TIMEPM2.5 concentration (ug/m3) STOCKTON

BAKERSFIELD

CORCORAN

VISALIA

CLOVIS

FRESNOSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-14 The southern San Joaquin Valley Air Basin experiences significant decreases or increases in AQI followed by relatively c onstant AQI, as may be seen in Kern County data presented in Figure 13. The signific ant decreases can occur in one day. The significant increases tend to take several days to build. The northern San Joaquin Valley Air Basin experiences more frequent significant increases and decreases in AQI, as may be seen in San Joaquin County and St anislaus County data presented in Figure 14 and 15. This is likely due to more frequent frontal passages in the northern San Joaquin Valley. In the sout h, a front that may have in fluenced the north valley may dissipate before reaching the southern San J oaquin Valley, resulting more potential for longer periods of stagnati on than the north Valley.

Figure 13 AQI in Kern County (Bakersfield) During the 2005-2006 PM 2.5 Season

0 50 100 150 200

11/1/200 5 11/8/200 5 11/15/ 200 5 11/22/ 200 5

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12

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200 5

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200 6 2/7/ 2 00

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### DATEAQI AQI decrease of 94 due to pre-frontal conditions & strong SE windsSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-15 Figure 14 AQI in San Jo aquin County (Stockton) During the 2005-2006 PM 2.5 Season

0 50 100 150 20011/1/200511/8/200511/15/200511/22/200511/29/200512/6/200512/13/200512/20/200512/27/20051/3/20061/10/20061/17/20061/24/20061/31/20062/7/20062/14/20062/21/20062/28/2006



### DATEAQI

Figure 15 AQI in Stanislaus County (Modesto) During the 2005-2006 PM 2.5 Season

0 50 100 150 20011/1/200511/8/200511/15/200511/22/200511/29/200512/6/200512/13/200512/20/200512/27/20051/3/20061/10/20061/17/20061/24/20061/31/20062/7/20062/14/20062/21/20062/28/2006



### DATEAQI A QI decrease of 101 due to pre-frontal conditions & strong SE windsSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-16 The most significant decreases in PM2.5 tend to occur when there is an air mass change associated with a vigorous frontal passage, typically in fall and winter. It appears that the mechanism that lowers the PM2.5 concentration is an air mass change and not necessarily by collision - coalescence or 'washout' by falling precipitation. As
discussed in section 1. b.1 of this Appendix

, precipitation can sometimes be associated with a significant increase in PM2. 5 in the San Joaquin Valley.

There is scientific support for why collision - coalesce nce may not be the primary
mechanism for PM2.5 removal. Collisions between water drops and particles are likely a function of gravitational, electrical and aerody namic forces. As a water drop falls in a cloud, it will collide with a very small amou nt of the particles in its path because aerodynamic forces tend to move the particles to the side, out of the drop path. If a collision of a water drop and PM2.5 particle occurs, this collision does not guarantee coalescence and removal of PM2.5. Rogers ( 1976) states that studies of aerodynamic forces in cloud drops have indicated that ve ry small drops cannot readily be made to collide. A small drop falling though a cloud of smaller dropl ets will collide with a very small percentage of drops in the drop path as long as the drop radius is less than 18 μ m (Rogers, 1976). The drops may bounce away fr om each other; they may coalesce and remain intact; and they may coalesce briefly and separate. The process is a function of water drop size, particle size, drop trajectories and external forces such as electrical charges. Therefore, some prec ipitation processes may not be sufficient to cause droplet capture of PM2.5. Air ma ss exchange appears to be a more effective PM2.5 removal process in the Valley.

Very large AQI and PM2.5 concentration changes can also occur over a short time period during relatively fair weather conditi ons. An AQI improvement of 89 occurred
from the 15th to the 16th of November 2007 in the north San Joaquin Valley (112 AQI to 23 AQI in Modesto) during a period of benign meteorological conditions. An AQI improvement of 67 occurred in the south San Joaquin Valley (in Visalia from the 16th to the 17th of November 2007). The improvement in AQI was likely due to a subtle improvement in dispersion conditions, as me teorological instrumentation recorded small changes in parameters. Wate r vapor satellite images indicated a very weak frontal passage occurred in zonal flow, resulting in a partial air mass change. The weak front was not evident in the surface weather maps . Physical evidence of the frontal passage was registered by an increase in the mixing height, a slight increase in surface winds and some high and middle clouds.

1.c.1 References for Significant Changes in AQI Due to Meteorological Events

• Mesowest website, http://www.met.utah. edu/mesowest/, Archived weather data

• Rogers, R. R. (1976), A short course in cloud physics, Pergamon Press

• UNISYS website, http://weather.uni sys.com/, Archived weather mapsSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-17 2. Physical and Chemical Processes

A variety of physical and chemical processe s occur in the atmosphere causing PM2.5 to form or to be removed, including fog proce ssing, dry deposition and nitrate production. Due to historical episodes fog relationshi p with particulate has been a subject for
extensive research. California and the S an Joaquin Valley experience high levels of nitrate particulate that is not a common pat tern for other states. The District is evaluating nitrate patterns and has identified information of potential importance for attainment planning. Car bon is another area requiring major continuing evaluation. Elemental and organic carbon are directly emitted, transfo rmed by chemical processes from gases to particles, and are sampled in e rror as particles by absorption of gases on sampler filters (sampler artifact ) making it difficu lt to assess.

Some factors have an effect but are consi dered as either less critical or not well quantified for current use in our decision-maki ng processes. Temperature and relative humidity affect properties of aerosols but have not been determined to be critical factors. Dry deposition of particulates has not been extensively studied. Particle deposition and aerosol re-evaporation flux are not well quantified and are not included in District forecasting and modeling.

2.a PM2.5 Formation and Removal During Fog Episodes

The District has examined fog effects on parti culate pollution to understand the role of fog on Valley air quality. Scientific investi gation of the effect of fog is warranted based
on historical events that demonstrate a le thal potential for severe fog episodes accompanied by PM2.5 high levels of car bon emissions. Probabl y the most famous episode occurred in London, England from 5 to 9 December 1952, resulting in the deaths of thousands. In the London episode, a cold fog developed resulting in the burning of more coal than usual. The polluted air mass was trapped under a strong temperature inversion layer, which acted like a lid on the air mass with coal soot accumulating to lethal levels. Research was conducted in the San Joaquin Valley to explore the consequences of severe fog event s in the Valley and determine the severity of PM2.5 during fog episodes.

While much has been learned about fog intera ctions with key inorganic aerosol species (e.g., ammonium sulfate and nitrate), it is only in recent years t hat investigators have begun examining interactions between fogs and carbonaceous aerosols and volatile organic compounds. The District has exami ned fog effects on particulate pollution through integrated projects included in the ma jor field study the California Regional Particulate (PM10/PM2.5) Air Quality St udy (CRPAQS) and through special technical studies and dedicated fog resear ch projects. Special projects related to fog were conducted in a preliminary field assessment for CRPAQS known as the 1995 Integrated Monitoring Study (IMS95) and in subsequent proj ects to assess fog and fog chemistry.
These studies examined PM2.5 formation and re moval during fog episodes. SignificantSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-18 CRPAQS findings concerning fog are pres ented in the following pages and include excerpts from a CRPAQS report written by J. Collett, Jr. et al (2005).

2.a.1 Fog Climatology

During the winter, persistent high pressure over the Great Basin creates a strong
subsidence inversion over California’s Ce ntral Valley, with a base typically a few hundred meters off the Valley floor and below the surrounding mountain ridges (Holets et al., 1981). With the help of t he mountains, this strong invers ion forms a lid over the air basin, trapping cool, moist air within the valley . Subsiding air results in clear skies, providing excellent conditions for strong radiative cooling at night and, if sufficient moisture is present, th e formation of dense, wi despread radiation fogs.

2.a.2 Fog Interactions with Gases and Part icles, Particle Formation and Removal

Fog is defined as water droplets suspended near the earth's surface that reduce visibility below 1 km (Huschke, 1959). Fog diffe rs from a cloud in that the base of fog is at the earth's surface, while clouds are above the surface. Fog water droplets are tiny, ranging in size from several micrometers to several tens of micrometers. This compares to the diameter of one PM2.5 particle for the sma ller dimension, ranging to several times the diameter of a PM10 particle for the largest fog par ticles. These drops form by water vapor condensation onto aeros ol nuclei known as cloud condensation nuclei (CCN). Water-soluble constituents in the CCN determine the initial composition of the fog.

Particles that become fog dr oplets by absorbing water vapor are subsequently removed by gravitational settling. Fog episodes caus e a net removal of PM by wet deposition. However, fog also provides an aqueous medium for formation of su lfate particulate. Fogs have two important, competi ng effects on aerosol populations:

• New aerosol mass formation through gas scavenging and chemical reaction in the droplets leading to non-volatile species (e.g. conversion of SO 2 to sulfate) that remain in the particle phase after droplet evaporation

• Aerosol scavenging followed by deposit ion through droplet settling and/or impaction

The relative importance of these two proc esses depends on the environment in which the fog forms and can include meteorologica l conditions, number and composition of aerosol particles, and gas phase chemical com position. The net effect of a fog episode depends on the pre-fog concentrations of parti culate precursors and availability of oxidants that are involved in the chemistry of particle formation, and the duration of the fog event. The net effect of a fog on atmospheric aerosol concentrations may change during a fog event; oxidation could be more im portant at the beginning of the fog eventSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-19 when reactant concentrations are higher, whil e deposition rates may increase over time with the growth of fog droplets.

Previous studies of sulfur oxidation in San Joaquin Valley fogs have shown that dissolved sulfur dioxide can react rapidly, ei ther being oxidized to sulfate or reacting with carbonyl compounds to fo rm hydroxyalkylsulf onic acids. Sulfate is both produced and removed by fog. The end result of a fog event may be eit her and increase or
decrease in the monitored levels of PM2.5 sulfate. Sulfat e particulate is removed by wet deposition during fog; however, fog dr oplets provide the aqueous medium for the production of sulfates, and the production of additional sulfate particulate by chemical reactions within the fog may over-balance th e wet removal and actually increase the
amount of sulfate PM2.5 in t he atmosphere. Whether sulfat e formation in fog exceeds sulfate removal by fog settli ng will vary from site to si te, depending on the duration of
event and concentrations of available reactant s to form additional sulfate particulate matter. Variations in fog dr op composition with size are known to influence the rates of
chemical reactions as well (e.g., Reilly et al., 2001).

Fog can process particles and gases as shown in Figure 16. Growth of droplets formed with aerosol CCN lead to removal of particles and gases from the air mass, which can
lead to a decrease in PM2.5 concentration.

Figure 16 Fog Processing of Particles and Gases

Fog droplet composition is also influenced by dissolution of soluble gases and aqueous phase chemical reactions as shown in Fi gure 17. The competition between removal and production processes leads to either an increase or decrease in PM2.5 concentration. These processes vary with fog characteristics.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-20 Figure 17 Fog Droplet Particle and Gas Scavenging Processes

Deposition due to fog drop sedimentation or impaction has been known to be an important removal process for atmospheric pol lutants for a long time (Waldman, 1986). Some studies have tried to assess the deposit ion fluxes by fog in the San Joaquin Valley by modeling (Lillis et al., 1999) or by measurem ents (Collett et al., 2001). However, there are relatively few measurem ents for atmospheric removal of fog solutes by drop deposition or how drop-size dependent fog composition affects removal rates for various chemical species.

While much is now known about the inorganic composition of San Joaquin Valley fog water, little is known about the scavenging and removal of carbonaceous aerosol by these fogs. Despite measurem ent of high total organic carbon (TOC) concentrations (e.g., during IMS95), the composition of the organic species ma king up this TOC is largely unknown in the San Joaquin Valley and elsewhere. Alt hough the expected net effect of San Joaquin Valley fog episo des is reduced atmospheric loadings of carbonaceous aerosol, the magnitude of this removal was unknown prior to CRPAQS. Secondary Organic Aerosol (SOA) formation (formation of organic carbon particulate from photochemical oxidation reactions of precursor gases) is reduced by decreased photochemical activity in circumstances where sunlight is reduced by fog or cloud cover. Clouds and fog reduce the photochem ical production of secondary organic aerosols by a factor of two or three from the maximum clear sky conditions because ofSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-21 reduced availability of photons. The therm odynamic interactions between fog droplets
and SOA are unknown.

2.a.3 Fog Research Results

In order to improve the under standing of the role fogs play in influencing aerosol concentrations in California’s Central Valley, Colorado State University (Collett et al, 2005) made measurements of the chemical and physical pr operties of fogs at several valley locations during the CRPAQS winter intensive. These observations subsequently formed the basis for a data analysis effo rt aimed at better characterizing fog composition and interactions between CRPAQS fogs and pollution levels, especially fine particles. The fog measurement campaign and subsequent data analysis phase produced a number of significant findings . These include the following major observations and conclusions made by J.Collett, Jr. et al (2005):

• Several fog episodes were characteri zed during CRPAQS. Most of the fog episodes were relatively shallow and featur ed very large droplets. Rarely did the top of the fog layer reach even 100 meters , in contrast to much deeper fogs observed during IMS95 and other studies in the San Joaquin Valley. The very large drops formed during CRPAQS probably re sult from strong radiative cooling directly from the drops themselves, thr ough the shallow fog layer, driving rapid condensational growth. These large drops se ttle from the fog relatively quickly, enhancing the ability of the fogs to rapidl y remove scavenged airborne particulate
matter.

• The chemical composition of the fogs during CRPAQS was dominated by nitrogen species, with import ant contributions also from organic compounds and
sulfate. Ammonium and nitrate were the most abundant indi vidual compounds; nitrite and sulfate were also found to be pr esent at significant concentrations, as were several organic compounds, includi ng formate, acetate, and formaldehyde. Abundant gas phase ammonia absorbed by fog drops helps keep the fog pH relatively high, with pH values typically well above 6. Material present in fog drops is derived from a combination of aerosol particle scavenging, gas absorption, and aqueous phase reactions.

• Comparison of Bakersfield fog com position measurements in CRPAQS and other recent San Joaquin Valley fog studies wit h measurements made in the 1980's reveals a statistically significant decrease in fog concentrations of sulfate and an increase in fog pH. These changes are c onsistent with intervening declines in
SO 2 emissions in the southern San Joaquin Valley, which would translate into less production of sulfate and greater avail ability of ammonia to raise fog pH.

• Comparison of fog composition during CRPAQS at Bakersfield, Angiola, and Helm reveals that Angiola and Helm, bot h rural sites, have generally similarSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-22 compositions. Urban Bakersfield fog contai ned greater concentrations of sulfate
and nitrite.

• The high pH droplets present in CRPAQS fogs make them effective atmospheric
reactors for dissolved sulfur dioxide. Bo th oxidation to sulfate and reaction with dissolved formaldehyde to produce hydroxymethanesulfonic acid (HMS) are important reaction pathways. Numerical simulations using a single drop fog chemistry model reveal t he importance of consideri ng effects of mass transport limitations on aqueous sulfur chemistry in the large fog drops observed in CRPAQS fogs.

• Preferential enrichment of major ion s pecies in small fog drops reduces most species’ deposition velocities below the deposition velocity for fog water. Nitrite, which was often enriched in large fog drops, exhibited deposition velocities higher than fog water. Accounti ng for drop size-dependent species concentrations is essential to accurately modeling rates of pollutant deposition in San Joaquin Valley fogs.

• Previous studies have documented the im portant role San Joaquin Valley fogs play in cleansing the atmosphere via particle scavenging followed by drop deposition. The importance of this mechanism was again observed during CRPAQS, with fog deposition fluxes c apable of reducing boundary layer fine particle concentrations of major species (e.g., nitrat e and ammonium) at a rate
on the order of 1 μ g/m 3 per hour. The fogs are also effective at scavenging and removing sulfate, but this removal is o ften offset by similar rates of sulfate production via aqueous phase oxidation of sulfur dioxide. Assuming a 100 m deep fog, Collett et al found that concent rations typically decrease as follows:

o SULFATE ~ 0.5 μ g/m 3 per hour

o NITRATE ~ 1 μ g/m 3 per hour

o AMMONIUM ~ 1 μ g/m 3 per hour

o TOTAL ORGANIC CARBON ~ 0.7 μ gC/m 3 per hour

• Results obtained during CRPAQS also indi cate the important role that San Joaquin Valley fogs play in scavenging and deposition of organic carbon. San Joaquin Valley fogs contain a rich mix of organic compounds, with major constituents including formaldehyde, forma te, and acetate. Many larger organic molecules are also observed, incl uding both polar and n on-polar compounds. Approximately 25% of t he fog organic carbon, on average, is present as undissolved, suspended material in the dropl ets. As much as half of the fog organic matter may be comprised of high molecular weight compounds, with molecular masses exceeding several hundred Daltons. Future studies are needed to better characterize this high mo lecular weight mate rial and determine whether it comes mainly from aerosol scavenging or is produced by aqueous phase reactions of lower molecular weight precursors.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-23 • The wide variety of organic compounds obs erved in the fogs indicates that carbonaceous aerosol particles from many source types undergo active fog processing. Observations of fog sc avenging of organic and elemental carbon also indicate the importance of fog proc essing of carbonaceous aerosol species. Organic carbon (OC) was observed to be more actively processed by CRPAQS fogs than elemental carbon. Differenc es were also observed between the efficiency of CRPAQS fogs in scavenging different types of fine particle organic carbon. Wood smoke particles were scavenged more efficiently and particles containing polycyclic aromatic hydrocar bons (PAH) less efficiently than fine particle OC as a whole. CRPAQS fogs were also observed to efficiently scavenge and remove the pesticide Dia zinon. Together, these observations suggest that fogs may be more effectiv e cleansing the boundary layer of OC from some source types than others, a topic deserving further attention in future
studies.

• Deposition fluxes of organic carbon in fog water were significant, yielding atmospheric removal rates on the order of 66 μ gC/m 2 hr. Because some of the fog burden of organic carbon is comprised of soluble, volatile organic compounds (VOC), a portion of the deposited carbon may be released back to the atmosphere when deposited fog water evaporates following a fog episode.

• Comparisons of fine particle organic ca rbon concentrations before and after fog episodes also suggests that aqueous phase reactions of dissolved VOC's may be important in producing new, secondary organic aerosol matte r. Much more work is needed to examine this hypothesis in future investigations.

• Measurements of the stability of carbonyl compounds in actual fog water reveal the importance of stabilizing these species as soon as possible following sample collection. Analysis of field-stabilized samples collected in Fresno fog episodes after CRPAQS reveal significant contribut ions of several carbonyl and dicarbonyl compounds to San Joaquin Valley f og organic carbon burdens. Glyoxal and methylglyoxal, in particular, were obser ved at substantial concentrations nearly equivalent to formaldehyde.

• The Carnegie Mellon University fog m odel, a 14-section size-resolved fog model with explicit fog microphysics, was us ed to simulate a CRPAQS fog episode and was able to predict the liquid water ev olution, bulk aqueous- phase concentration measurements, drop size-resolved trends, and deposition fluxes for a number of species in close agreement with observed values. The predicted evolution of the distribution of aerosol species like su lfate, nitrate, ammonium, and chloride indicated significant differences over the course of fog processing. Different sizedependent processes controlled the size-dis tribution development at different stages of fog processing. Early in proc essing, the dissolution of soluble gases and rapid aqueous phase reactions cont rol the development of the size distribution. At later times, the effect s of deposition begin to dominate, and pushSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-24 the peak of the distribution towards smalle r diameters. Model predictions of the evolution of most key species app roached bulk aqueous-phase concentration measurements. During the early stages of the fog, the behavior of species originating partially in the gas phase (NO 3 - , SO 4 2- ) was heavily influenced by dissolution into the droplets and rapid aqueous phase reacti ons. Following these initial peaks in aqueous phase concentra tions, deposition began to dominate, and the species were gradually depl eted from the fog layer.

2.a.4 Fog References

• Collett, J.L.J., Herckes P., Chang H., and Lee T., Pandis, S.N., and Fahey K. (2005)
Examination of the Influence of California Regional Partic ulate Air Quality Study Fog Episodes on Aerosol Formation and Removal, Submitted to: San Joaquin Valleywide Air Pollution Study Agency, January 13, 2005

• Collett J. L., Sherman D. E., Moore K. F., Hanni gan M. P., and Lee T. (2001) Aerosol particle processing and removal by fogs: observations in chemically heterogeneous central Calif ornia radiation fogs. Water, Air, Soil Poll: Focus. 1 , 303-
312.

• Holets, S. and Swanson, R.N., 1981. High inversion fog episodes in central
California. Journal of Applied Meteorology , 20: 890 - 899.

• Huschke, R. E. (1959), Gl ossary of Meteorology, American Meteorological Society

• Lillis, D., Cruz, C.N., Collett, J., Richards , L.W. and Pandis, S.N., 1999. Production and removal of aerosol in a polluted fog la yer: model evaluation and fog effect on
PM. Atmospheric Environment , 33(29): 4797-4816.

• Pandis S. N., Cruz C. (1997) Techni cal Support Study 11. Investigating the dynamics and chemistry of fog formation and dissipation. Prepared for the California
Air Resources Board

• Reilly, J. E., Rattigan, O. V., Moore, K. F., Judd, C., She rman, D. E., Dutkiewicz, V. A., Kreidenweis, S. M., Husain, L. and Coll ett, J. L., Jr., 2001. Drop size-dependent S(IV) oxidation in chemica lly heterogeneous radiation fogs. Atmospheric
Environment , 35(33): 5717-5728.

• Waldman J. M. (1986) Depositional aspects of pollutant behavior in a fog. Ph.D. Thesis, Caltech. Pasadena, California

2.b Dry Deposition

Fine particles are small enough that the ra ndom forces from collisions with gas molecules largely overcome gravitational forces. Fine particles tend to follow air streams and are typically not removed by impac tion. As a result, they are not easily
traced back to their indi vidual sources.

Fine particles formed from accumulation proc esses are significantly larger than gas molecules and their diffusion velocity is low. These particles have very long half-lives inSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-25 the atmosphere, travel long distances, and te nd to be more uniformly distributed over large geographic areas than coarse-mode parti cles. Removal by dry deposition is inefficient since they do not readily diffuse through the boundary layer of still air next to surfaces. The atmospheric half-life of fine accumulation particles with respect to dry deposition is on the order of weeks; however , removal occurs when the particles absorb water, grow into cloud droplet s, grow further to raindrops , and fall out as rain. This process reduces the typical atmospheric half-life to a few days.

Ultrafine or nuclei-mode particles, formed by nuc leation of low saturation vapor pressure substances, tend to exist as disaggregated indivi dual particles for very short periods of time (less than minutes) in the ambient atmo sphere and tend to age rapidly into larger accumulation particles that may be disper sed more widely over long distances.

Secondary fine particles are formed by atmos pheric transformation of gases to particles. Atmospheric transformation can take place lo cally during stagnations or during transport over long distances. Fine particles have very low dry deposition velocities, which contribute to their uniformity throughout the ai r mass. Aerosol effects on visibility and climate, through light scattering and changes in cloud microphysics, pr imarily arise from fine particles.

Nitrates and carbon are the two largest co mponents of PM2.5 and their atmospheric behavior is entirely different.

“High concentrations of PM organic ca rbon (OC) were spatially limited to core urban sites while high concentrati ons of PM ammonium nitrate were regionally distributed throughout the SJ V. Concentrations of PM and its precursors were typically lower at the elevated sites surrounding the SJV than at monitoring sites located on t he SJV floor....At distances more than 50 km from the urban areas, OM conc entrations typically declined by a
factor of three or more. Emissions of OM at the urban core are either not rapidly transported to the rural sites or are diluted too much to substantially impact rural sites. Conc entrations of OM at elevated sites were comparable to concentrations at rural sites on the Valley floor....Overall, these spatial patterns of OM suggest that the impact of emissions was largely confined to t he local area and OM concentrations were unevenly distributed over the duration of the episode.

The contrast in spatial variability between the ammonium nitrate and OM components of PM2.5 in the SJV winte r episodes provides information on the spatial extent of the production of ammonium nitr ate. PM2.5 OM and ammonium nitrate are both subject to the same meteorological transport conditions, yet ammonium nitrat e concentrations are relatively homogeneous and OM concentrations ar e much higher in the urban source areas. In addition, OM and ammonium nitrate components are expected to have the majority of t heir mass in a similar size fraction (PM0.1 to PM1) (Lighty et al., 2000; Hughes et al., 1999; Bench et al.,San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-26 2002) and, therefore, the rates of removal shoul d be approximately the same. In summary, the likely explanat ion for the difference in spatial variability is the spatial di stribution of the emissions or precursors. Primary OM emissions occur predominantly fr om mobile sources and wood smoke
located in urban areas. The formation of ammonium nitrate from NOx precursors (Lurmann et al., 2004) must occur throughout the SJV to account for its spatial homogeneity.

High concentrations of PM organic ca rbon were spatially limited to core urban sites while high concentrations of PM ammonium nitrate were regionally distributed throughout the SJ V. The regional homogeneity of
ammonium nitrate concentrati ons coupled with the stagnant wind conditions provides evidence that produc tion of ammonium nitrate occurs at similar rates throughout the valley. In contrast, the OC component of PM indicates that production rates were much higher in the urban areas than at rural sites.” (referenc e citation follows in 2.b.1)

2.b.1 Dry Deposition Reference

• Background and Boundary Conditions for Pa rticulate Matter and Precursors in the San Joaquin Valley in Winter, Tec hnical Memorandum STI-902325-2779-TM, Michael C. McCarthy, Hilary R. Hafner , Steven G. Brown, Fredrick W. Lurmann, Paul T. Roberts, Sonoma Technology, Inc., 1360 Redwood Way, Suite C, Petaluma, CA 94954-1169, July 29, 2005

2.c Nitrate Events

Nitrate particulates are generally low in summer and fall, partially due to breakdown of the particles back into gaseous precursors. Photochemical reactions reduce nitrates; therefore, overcast conditions support increase in nitrate production. Valley summers have infrequent cloud cover. Smoke from fi res whether aloft or at the surface can reduce photochemical energy penetration to the surface allowing more particle
formation. As with all other particulates, accumulation to high concentrations is also dependent on stagnation events to allow the material to accumulate.

2.c.1 Relationship Between Carbon and Hy droxyl Radicals and Nitrate PM2.5

Nitrate particulate levels in the San J oaquin Valley declined shar ply after the 2000-2001 winter. It is difficult to isolate meteorologic al variations from other factors to determine a strong cause and effect relationship. However, the most pronounced change (during the time of year that the ni trate levels increase) was the introduction of different smoke management practices including the voluntar y curtailment (commencing in 2001) and mandatory curtailment (commenc ing in 2003) of residential wood combustion when air quality conditions were fore cast to be unfavorable.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-27 Since the primary emissions from resident ial wood combustion are carbon and VOC, the link between reduced burning and reduced nitrate particulate levels is not automatically evident. EPA has established that hydroxyl radicals, released by chemical reaction from organic VOC, are the primary mechanism for much of the atmospheric chemistry for both ozone and particulates. The role of hydroxyl radicals in ozone and particle formation is a key concept in EPA's "One Atmosphere" technical evaluation. Nitrate particulates require hydr oxyl radicals to form particulate. This establishes the possible effect of receiving multiple benefits from reducing carbon and organic carbon emissions, in that not onl y will carbon be reduced but also secondary particulate formation including nitrates and secondary organic aerosol (SOA).

Additional evidence supports the relations hip between carbon and nitrate particulate formation. A sharp increase in nitrate appears to occur during periods when the air shed is being significantly impacted by wildland fire smoke. During several wildfires that occurred during the summer and fall, when nitrat e is usually at very low concentrations, elevated levels of nitrates occurred on a daily basis. This conveys that either the fires produce much more nitrate than expected and tr ansport it to distant areas or that the carbon and hydroxyl radicals promote nitrate formation in the local area. Either
circumstance connects fires to nitrates. The carbon in the smoke plume provides carbon nuclei and/or organic carbon radicals that can initiate nitrate particle formation. The District has conducted preliminary evalua tion of two case studies that provide supporting information. Further evaluation of these events and other similar events may be warranted to establish a confirmed finding.

Figure 18 Daily average nitrate and maxi mum hourly nitrate by day at Fresno - First Street monitoring stat ion affected by Day Fire

Nitrate Concentrations - Fresno - First Street

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9 /27/2006

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1 0/15/200 6Nitrate (ug/m3)

Average Maximum HourSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-28 Figure 18 shows high nitrate concentrations during a period of smoke production from large wildland fires. Typical nitrate levels at this time of year (September and early October) are less than ten micrograms.

Figure 19 is a smoke plume simulation using the CANSAC MM5 meteorological model. At the time of this analysis, 10:00 PST on October 10, 2006, the smoke plume was projected to be over the Fresno area. T he CANSAC simulation has not been confirmed for accurate fire inputs for th is simulation. The value of assessing this type of event is that the path and origin of emi ssions provide a more direct linkage to a fire event than when the emissions path crosses through large cities. Events of this type do not occur frequently and events that contain emissions mi xed from many source areas are more
difficult to resolve into c ause and effect relationships.

Figure 19 Wildfire smoke simulation for October 10, 2006, at 10:00 PST, displaying peak particulate con centration over the Fresno areaSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-29 In Figure 20, the observed increase in nitrat es occurred in the hours immediately after the projected arrival of the smoke plume in Fresno. This indicates that the smoke plume itself was not high in formed nitrates , but provided carbon nuclei and/or organic
carbon radicals that initiat ed nitrate particle formation. After departure of the smoke plume, nitrate levels rapidly returned to am bient levels that were measured before the arrival of the smoke plume.

Figure 20 Hourly nitrate (ug/m3) at Fr esno - First Street monitoring station, displaying increase in ni trate on October 10, 2006, in the hours following arrival of the smoke plume

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 10/10/2006

The case studies, and unexpected decline in nitr ates after establishing stronger burning restrictions, establish a strong likelihood t hat burning controls provide more than a
carbon benefit for the District. Understanding and confirmi ng this relationship through
future research and technical evaluation is valuable for effective PM2.5 planning.

3. Emissions Related Issues

High levels of PM2.5 may occur anytime th roughout the year if influenced by unusual local or regional emission activity. Wildland fires and 4 th of July firework activity have been noted as causing PM2.5 levels to be hi gher than what is typically experienced during the summer and fall. Day of the week activity variations and holidays during the fall and winter have the potential to cause higher PM2.5 levels due to residential wood burning.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-30 3.a Day of week and Holiday Effect

• Day Of The Week Use of fireplaces tends to increase on cold winter weekend nights. PM2.5 can increase on Friday, Sa turday and Sunday when residential wood combustion may be higher than during the workweek.

• Holiday On winter holidays, residential wo od combustion from fireplaces can substantially increase, result ing in a significant increas e in the particulate matter concentrations. Days around Thanksgiving, Christmas and New Year’s Day tend to have higher PM2.5 concentrations.

• 4 th of July PM 2.5 concentrations increase signifi cantly during the ev ening of July 4 and continue into the early morning hours of Ju ly 5 due to fireworks emissions. This effect is especially pronounced during perio ds of stagnant weather conditions. On July 4, 2007, PM2.5 increased to very hi gh concentrations during the time of day when fireworks were used, as shown in Fi gure 21. This coincided with a period of stagnant conditions, which resulted in PM2. 5 concentrations remaining high into the early morning hours of July 5. Fire works emissions are categorized as an Exceptional Event by EPA policy, but the Distr ict is proposing a feasibility study to investigate the possibility for cont rols on fireworks (see Chapter 6).

Figure 21 Fireworks Emissions Effect on PM2.5, July 4 th and 5th, 2007 Data in this plot is preliminary and subject to revision

0 200 400 600 800 1000 120013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:000:001:002:003:004:005:006:007:008:009:0010:0011:0012:00

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Date and TimePM2.5 (ug/m3) Turlock

Modesto

Fresno

Clovis

Corcoran

Visalia

Bakersfield California Street

Bakersfield Golden State HighwaySan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-31 3.b Wildland Fires

Wildland fires can have a significant effect on particulate air pollution. Wildland fires can be ignited by human activity and by light ning. These fires are either suppressed (put out) or managed (allowed to burn) as a controlled burn. Part iculate from wildland
fires can increase surface PM 2.5 concent rations. Figure 22 shows smoke from the Day Fire being transported to the San Joaquin Valley. It should be noted that large wildfires may release particulates in amount s that dwarf the District daily emission inventory, causing impacts that cannot be fu lly remediated by District action to curtail local emissions. The impact of a wildfire will depend on whether the smoke passes aloft
over the District or mixes into the surface air. Wildfires release carbon, NOx and VOC's. Some of the VOC's that are emitted by wildfires are classified as air toxics.

Figure 22 Smoke from the Day Fire Tr ansported to the San Joaquin ValleySan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-32 3.c Agricultural and Prescribed Burn Management

The District's agricultural, hazard reduc tion, and prescribed burn programs permit, regulate, and coordinate the use of burni ng in the San Joaquin Valley air basin to minimize smoke impacts on the public. The goal of these smoke management programs is to minimize air quality impacts by allowing agriculture, hazard reduction, and prescribe burning to occur on days w hen dispersion is adequate enough to carry emissions away from sensitiv e receptors. The District has developed a stat e of the art Smoke Management System (SMS) that allows t he District to permit agricultural burning
in some areas of the District and not allow agricultural burning in others, based on dispersion conditions and air quality. The SMS reduces smoke impacts by preventing burning from occurring in a concentrated area or in locations that are forecast to have poor air quality, while allo wing agricultural burning in areas that have adequate dispersion and good air quality. The Distr ict manages the burn programs daily to determine if the potential emissi ons will impact the air quality in the air basin. On days when the air quality is predicted to be marginal or poor, the District severely restricts, or does not allow, agricultural, hazard reducti on, and prescribed burni ng to occur. When air quality conditions improve, the District a llows open burning as di spersion conditions and air quality dictate.

Applicable District rules regulating burning activity: Rule 4103 Open Burning - Agriculture Rule 4106 Prescribed Burning and Hazard Reduction Burning

3.d Residential Wood Burning Program

The purpose of the District's re sidential wood burning program is to protect the public by limiting the emission of particulate ma tter from wood burning fireplaces and wood burning heaters when air quality conditions are unfavorable for dispersion of the emissions. The District discourages the public from burning when the Air Quality Index (AQI) is greater than 100. An episodic cu rtailment for a geograp hic region is declared whenever an Air Quality Index value of 150 or greater is predicted for the geographic region (county). An episodic wood bur ning curtailment may be issued during the
months of November thr ough February. Operation of wood burning fireplaces and wood burning heaters is prohibite d in the specified region when the District declares a curtailment, except for certain exemptions (e . g. device is sole source of home heat).

Applicable District rule regulating burning activity: Rule 4901 Wood Burning Firepl aces and Wood Burning HeatersSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-33 3.e Recent Particulate Research Studies

Evaluation of Rule 4901 This study (Lighthall, 2007) is designed to provide the District with a comprehensive evaluation of Rule 490 1, which regulates residential wood combustion. Rule 4901 set in place an AQI- triggered ban on wood burning in areas of the San Joaquin Valley that have natural gas service and are below 3,000 ft elevation. In particular, the study will assess the c ontribution of the Rule to reduced PM2.5 emissions in urban areas of the region and to corresponding reductions in health impacts (mortality and morbidity). In addition , to contributing to the larger body of knowledge about the health effect s of PM2.5 exposure, the st udy will provide the District
staff and Board with a solid scientific basis for determining whether additional
restrictions in wood burni ng will be justified.

PM Emission Factors and Inven tories from Leaf Blowers The District funded the University of California at Riverside - College of Engineering Center for Environmental Technology (CE-CERT) to design a st udy and perform measurements and data analysis to determine particulate matter emissi ons from leaf blowers and to obtain a PM emission inventory from their operation in the District. The following is an excerpt from the executive summary of t he final report (Fitz, 2006).

The approach used to measure emissions fr om leaf blowers and alternative devices (vacuums, rakes, and brooms) was to operate the devices over a measured area in a tent-like enclosure. In this enclosure, the leaf blower (or other device) could be used in a normal manner while allowing t he PM emissions to be confined for quantification. PM
concentrations were measured with real ti me sensors. Measurements were made for total suspended particulate matter (TSP), parti culate matter (PM) with an aerodynamic diameter less than ten microns (PM10) and particulate matter with an aerodynamic diameter less than 2.5 microns (PM2.5). The amount of PM produced per unit area was then calculated by multiplying the conc entration once it stabilized (when it became uniformly mixed) by the volume of the enclo sure and dividing by the area treated. To directly compare the PM emission characteri stics of blowing, vacuuming, raking, and sweeping, the surface to be treated in the enclosure was loaded with surrogate debris. To develop the composition of this surrogate ma terial, bulk samples were collected from areas on the University of California, River side (UCR) campus where leaf blowing was
about to be conducted to determine the mass of soil and vegetative matter present where these cleaning activities are conduc ted. The test system was then used to measure emissions from leaf blowing over surfaces where leaf blowing is typically conducted and over surfaces where a surrogat e mixture of soil (obtained from the San Joaquin Valley) and vegetative ma tter was deposited by our staf f. A number of emission tests were performed using the natural/indigenous material at the CE-CERT facility in Riverside and at the UC Kearney Agricu ltural Center in Parlier, CA.

Health Effects of Airbor ne Fine Particles (PM 2.5 ) and Ozone The goal of this study (Tyner, 2007) is to determine whether ex posures to airborne fine particles (PM 2.5 ) and ozone (O 3 ) induce lung inflammation that is rela ted to exacerbations and severity ofSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix E: District Additions to the Conceptual Model
2008 PM2.5 Plan E-34 disease in nonatopic asthmatics and, reflecting the multi-factorial w eb of causation of asthma, how this relation is modified by vi ral infection and genetic predisposition. The development of urinary PAH-quinone biomarke rs to monitor indi vidual exposure to
PM 2.5 provides an enhanced method for examin ing associations between exposures and health outcomes. In addition, measurement of organic species (2-3 ring PAH and oxygen derivatives) and wood-smoke trac ers (levoglucosan) in ambient PM 2.5 samples and subject urine samples provides informati on on the impacts of PM composition and reactivity on respiratory health and potential a ssociations with exacerbation of asthma.

Ambient 24-hr PM 2.5 filter samples will be obtai ned from the Clovis and Winery monitoring sites throughout the study perio d and analyzed by project investigators (Hasson Lab). Filter samples will be collect ed 1-in-3 days from October 2007 – March 2008 and 1-in-6 days from April 2008– September 2008 per US EPA PM 2.5 monitoring schedule. Following gravimetri c analysis by the Ventura County Air Pollution Control District Lab, filters will be archived for 30 days (stored under controlled temperature/humidity) after wh ich filters will be returned to the District. Filters will then be retrieved from the District by project investigators and filters will be extracted in organic solvent and solute composition (PAH, PAH-quinone, levoglucosan) and reactivity (ROS generation) will be determined.

3.e.1 Recent Particulate Research Study References

• Fitz, D. R., Pankratz D., Chitjian, M., Bristow. J., Pe terson S. (2006) Particulate
Matter Emissions Factors and Emissions Inv entory from Leaf Blowers in use in the San Joaquin Valley, CE-CERT, UC Riverside

• Lighthall, D (2007) Email communication

• Tyner, T. (2007) Email communication

Additional links to peer-review ed publications that complem ent the staff reports and memos cited in this Appendix:

Basic Characterization: http://www.arb.ca.gov/a irways/CRPAQS/PM_DA/fina l/Chowetal2006JGRChemC ompSpatioVar.pdf

Fog: http://www.arb.ca.gov/air ways/CRPAQS/PM_DA/final/Herckesetal2005JAWMAF ogOverview.pdf

Secondary Aerosols: http://www.arb.ca.gov/a irways/CRPAQS/PM_DA/fina l/Lurmannetal2006JAWMAS JVFresnoSecAerosol.pdf

Transport: http://www.arb.ca.gov/a irways/CRPAQS/PM_DA/fina l/MacDonaldetal2006JAWM ASJVPMTransport.pdf