1. Preparation of Fine Particulate Emissions Inventories
Chapter 1 - PM 2.5 Overview

2. What will We Discuss in Chapter 1 and Why is This Information Important?
After this lesson, participants will be able to describe:
the general composition of fine particulate matter in the atmosphere
how fine particulate matter are formed
typical composition of ambient air in 2 western areas
sources that contribute to the formation of fine particulate matter, nationally and in this area
After this lesson, participants will be able to describe:
the general composition of fine particulate matter in the atmosphere and in 2 western areas
how fine particulate matter are formed, and
sources that contribute to the formation of fine particulate matter, nationally and in this area.

3. What will We Discuss in Chapter 1 and Why is This Information Important?
puts the local inventory efforts in perspective
shows how source types fit into the overall accounting of PM2.5
provides a foundation for setting inventory priorities in your area
Why is this information important?
puts the local inventory efforts in perspective,
shows how source types fit into the overall accounting of PM2.5
provides a foundation for setting inventory priorities in your area

4. PM2.5 In Ambient Air - A Complex Mixture
This graphic illustrates the difference between primary, or directly-emitted particles and secondary particles, which are formed in the atmosphere from precursor gases.
Notice the 2 main types of primary particles – carbon and crustal.
Primary particles contain:
elemental carbon (EC)
primary organic aerosol (POA)
small amounts of crustal matter and other materials.
The secondary particles are formed from precursor gases and the amount formed and the rate of formation depends on the availability of gases AND atmospheric conditions.
Secondary particles contain:
secondary organic aerosol (SOA) formed from volatile organic compounds
ammonium sulfate formed from SO2 and ammonia gases
ammonium nitrate, formed from NOx and ammonia gases.
The term total carbonaceous matter is used to describe the combined mass of EC, POC, SOC and the associated O and H.
Some secondary particles are formed rather quickly and others form over a period of days or weeks.
So, the precursors emitted upwind of your area may affect your air quality.
Likewise, precursors emitted in your area may affect other areas downwind.
It’s a complicated process and chemical transport and transformation models are needed to sort it all out.
But, the models can’t work without a good emissions inventory.

5. PM2.5 Composition Definitions
Crustal ~ Metallic oxides in earth’s crust
Fugitive Dust ~ Crustal matter emitted into the air directly, not thru a stack or vent.
Sulfate ~ H2SO4 (condensed), (NH4)HSO4 (NH4)2SO4
Nitrate ~ NH4NO3
Organic Carbon ~ OC
Organic Matter ~ OC + the associated O & H
CEm or CAm ~ Multiplier to convert OC to OCM
Elemental Carbon ~ EC
Primary ~ Directly emitted
Secondary ~ Formed in air from precursor gases (generally considered to be all PM2.5)
Lets review some of the terminology we’ll be using today
Crustal ~ Metallic oxides in earth’s crust
Fugitive Dust ~ Crustal matter emitted into the air directly, not thru a stack or vent.
Sulfate ~ H2SO4 (condensed acid droplets), (NH4)HSO4 ~fully neutralized sulfate and
(NH4)2SO4 ~ bisulfate
Nitrate ~ NH4NO3
Organic Carbon ~ OC
Organic Matter ~ OC + the associated O & H.
Note that this is written OCM to signify that the “matter” (mostly O & H) is added. 
Sometimes a number (e.g., 1.4, 1.8, 2.2) follows the M to show how much “M” is added. 
The number represents the ratio OCM/OC.
Elemental Carbon ~ EC
Primary ~ Directly emitted
Secondary ~ Formed in air from precursor gases (generally considered to be all PM2.5)

6. Why is Ambient Composition Important?
Identifying important source types on days with high PM2.5 concentration
Help prioritize inventory efforts
Carbonaceous vs. Crustal
Sulfate vs. Nitrate
Role of Ammonia
Help in benchmarking the validity of the EI
For example, in the previous slide we saw some key differences in the PM-2.5 composition in Anchorage and the Boise area.
In Boise: Less carbon – more nitrate - lower ratio of primary to secondary PM than in Anchorage
Ambient compositional analysis (including urban excess) can
help identify important source types on high PM-2.5 days
suggest the spatial extent of sources (urban vs. regional)
help prioritize EI efforts

7. PM2.5 Composition (cont’d)
Other characteristics: Sulfate, Carbon & NO3
Sulfate forms slowly, over long distances
Sulfate patterns relatively “flat” over large regions.
Regionally disbursed sources
Carbon has both regional & urban components
High Nitrate concentrations are usually
more localized
tend to form in urban areas, or
where abundance of animal or fertilizer NH3
Research has shown that…
Sulfate forms slowly, over long distances, so
This causes sulfate patterns to be relatively “flat” over large regions
Carbon concentrations substantially higher in urban areas
“Urban” Carbon is usually mobile source-related
“Rural” Carbon usually from fires
Chemical analyses such as radiocarbon can confirm this.
High nitrates are usually more localized, more likely in urban areas and associated with overabundance of NH
The monitoring data highlights the regional scope of the problem of sulfate emissions.
There is a significant excess of carbon in the urban areas, as evidenced by its marked increase from rural to urban areas.
Urban air quality data is often compared to rural air quality data by noting the amount of “urban excess” for a particular component.

8. PM2.5 Composition Varies Across U.S.
Northwest
Midwest
In the Northwest, Sulfate is low, but OC is high and there is some nitrate.
In the Midwest, we see much more sulfate and a little less OC, but even more nitrate.
In the Southeast, there is also much sulfate and as much OC as in the NW, but almost NO nitrate.
Why?
Much more hydroelectric power in NW whereas coal-fired (SO2-emitting) utilities prevail in MW and SE
Perhaps in the SE, the available Ammonia couples with the Sulfate.
There is much more ammonia available in the MW and much less in the NW
Temperatures and ozone chemistry may also play a role
Southeast
Sulfate Nitrate EC OC Crustal

9. Rough Estimate of Secondary Material in the Anchorage Area (~40%)
2002 Anchorage, AK PM
2.5 9% 3%
10%
12%
56%
CRUSTAL
AMMONIUM
SULFATE
NITRATE EC
OCM(1.4)
Ammonium Sulfate and Ammonium Nitrate together comprise about 40% of the ambient air in Anchorage.
Nitrate is lower than in Boise, at only 10%, even higher when the ammonium is added in. A closer look at the seasonality of the nitrate and what else is occurring in that season will prove useful.
Recall, we expect to see substantial secondary OC in Fairbanks as well under conditions of summertime wildfire smoke incursions.

10. Estimate of Primary Material in the Air in Anchorage Area (~60%)
2002 Anchorage, AK PM2.5 9% 3%
10%
12%
56%
CRUSTAL
AMMONIUM
SULFATE
NITRATE EC
OCM(1.4)
Crustal makes up only 9% of the ambient air in Anchorage, but carbonaceous particles are about almost 70%. Some of this OCM is secondary, perhaps 1/3 for discussion purposes.
If the OCM is 2/3 primary, then primary materials comprise about 55-60% of the annual average composition in Anchorage.
We couldn’t locate speciated data for Fairbanks.  Fairbanks problems are mainly wintertime, attributed to burning more fuels then, cold weather inversions and being surrounded on 3 sides by hills.  There is some mention of smoke incursions in the summer.  Thus, we would expect to find substantial Primary OCM in Fairbanks in the Winter and both primary and secondary OCM there in the summer.

11. Annual Ranges:
Crustal………<5%
Total C.…60-90+%
Am Sulfate 10-30%
Am Nitrate… <5%

12. Composition AND Urban Excess
Components of PM are higher in the urban area than in the surrounding area
Urban Excess is that part of the urban AQ that is higher than in surrounding areas.
Simplistically, urban excess is assumed mostly associated with urban sources
When we see higher concentrations of carbon (or Nitrates) in an urban area, we call it URBAN EXCESS
Carbon and Nitrate usually have an “urban excess” – Sulfate usually does NOT.
“Urban” Carbon is usually due to mobile sources and/or residential wood burning
“Rural” Carbon is usually from fires
Chemical analyses such as radiocarbon can confirm the inventory’s split between mobile biomass-related carbon.
Urban Nitrates sometimes exacerbated by wintertime inversions
The next slide illustrates this concept occurring in Atlanta
Wonderlane

13. “Urban Excess” in Atlanta, GA
Sulfate
Est. Ammonium
Nitrate
EC+OCM
Crustal 2 4 6 8 10
ug/m3
Atlanta, GA / Ring of Rural Locations
Bottom: Regional Contribution
Top: Urban Excess
Rural Monitors
used for Comparison
( + )
Draft Analysis
Data from Atlanta, GA is presented in this graph to illustrate the “urban excess” concept, where the higher urban concentrations are on the top part of the bars.
This exercise can (and should) be repeated in any area where sufficient data are available.
Note that in the Atlanta area:
Nearly all sulfate is associated with the regional contribution; this indicates that the sulfate in Atlanta is only 10-15% higher in concentration than the sulfate that you find in the surrounding rural sites.
Since most of the ammonium is associated with sulfate, ammonium concentrations follow a similar pattern.
Nitrate and carbon concentrations are nearly twice as high in urban areas as in rural areas, a significant “excess”.
The concentration of total carbonaceous material is greater than the sulfate concentrations in Atlanta and the concentration of crustal material is very small.
This “urban excess” phenomenon is found in most urban areas, but the amount of the excess varies and may or may not be significant in all components in all areas.
The amount of the excess in your area could indicate which sources or precursors that are emitted locally are important contributors to high PM-2.5
Let’s look at the composition of PM in a couple of Western urban areas…
This exercise can (and should) be repeated in any area where sufficient data are available.

14. How is Anchorage’s Air Different from Atlanta’s?
Annual Primary PM2.5
in Atlanta
Annual Primary PM2.5
in Anchorage
Crustal (<< 5%)
EC + ~ 2/3- of OCM (~ < 50%)
So, <50% of annual mass is Primary
Varies day – by - day
Crustal (9%)
EC + ~ 2/3+ of OCM (50+ %)
So, ~ 60% of annual mass is Primary
Varies day – by - day
Crustal makes up only 9% of the ambient air in Anchorage, but carbonaceous particles are about almost 70%. Some of this OCM is secondary, perhaps 1/3 for discussion purposes.
If the OCM is 2/3 primary, then primary materials comprise about 55-60% of the annual average composition in Anchorage.
We couldn’t locate speciated data for Fairbanks.  Fairbanks problems are mainly wintertime, attributed to burning more fuels then, cold weather inversions and being surrounded on 3 sides by hills.  There is some mention of smoke incursions in the summer.  Thus, we would expect to find substantial Primary OCM in Fairbanks in the Winter and both primary and secondary OCM there in the summer.
Characteristics of the Secondary and Urban Excess are also different

15. Overview of PM2.5 Sources in SE U.S.
PM2.5 (OC, EC, Ammonium Nitrate and Sulfate, Crustal)
Open Fires (primary OC, EC, VOC, NOx & NH3)
Wild & Prescribed fires, open burning, land clearing debris
Motor Vehicles (NOx, VOC, NH3, OC, EC)
Non road emissions (NOx, VOC, NH3, OC, EC)
aircraft, lawn, construction, and agricultural equipment.
Residential Wood Combustion (OC, EC, VOC)
Boilers (OC, EC, VOC, NOx, SO2, some crustal)
Fugitive Dust (mostly crustal, some OC, EC)
More ~ Agriculture, unpaved roads, Construction
Lesser ~ anti-skid sanding, windblown dust
PM-2.5 sources are mainly fugitive dust, open fires, mobile sources and the precursors of Ammonium Nitrate and sulfate
Fugitive dust is mostly crustal material, but also contains OC and EC. Ag tilling & harvesting, anti-skid materials on paved roadways, unpaved roads and windblown dust off of sparsely vegetated, disturbed surfaces
Open fires emit primary OC and EC as well as VOC, ammonia and some NOx
Motor vehicles emit most of the NOx in urban areas unless substantial utility or manufacturing boilers are present.
Non road sources are also important for OC, EC, NOx and Ammonia and residential woodstoves and fireplaces emit OC and EC
For example, NOx in Treasure valley ID is of concern because it contributes to the formation of ozone and PM2.5. The largest source of NOx in Treasure Valley is motor vehicle emissions. Other NOx sources include open burning and non-road vehicle emissions such as those from aircraft and from lawn, construction, and agricultural equipment. 

16. Overview of PM2.5 Sources in U.S.
PM2.5 (Crustal, OC, EC, Ammonium Nitrate) cont’d
Misc VOC Sources (precursor to secondary OC)
Household and industrial products, such as paints and varnishes, cleaners, disinfectants, and degreasers
Fuel combustion and the handling and distribution of fuel
Dairies and other livestock waste
Wild & Prescribed fires  
Misc Ammonia Sources (precursor to ammonium nitrate)
During wintertime stagnation, air can be ammonia-rich
Livestock wastes from dairies and agricultural operations
Wild & Prescribed fires
Volatile Organic Compounds (VOCs)
Volatile organic compounds (VOCs) are common in household and industrial products, such as paints and varnishes, cleaners, disinfectants, and degreasers. All of these products can release organic compounds. Fuel combustion and the handling and distribution of fuel is a significant contributor to the VOCs in the air throughout the Treasure Valley. VOCs are of particular concern in the Treasure Valley because they are a precursor to ozone but they also can form secondary organic particulate, an important component of PM2.5.
Ammonia
Ammonia is a pollutant of concern due to its role in the formation of PM2.5. Air in the Treasure Valley (TV) has been found to be ammonia rich during wintertime stagnation events, the atmosphere was ammonia-rich, creating prime conditions to chemically form PM2.5. Livestock wastes from dairies and agricultural operations are the largest source of ammonia emissions in the valley. Results of studies in the TV showed that the largest source of ammonia in the (accounting for 64% of all emissions), was livestock urine and solid waste.
Ammonia and VOC emissions from large dairies are very difficult to accurately quantify. Properly designed, sized, and maintained lagoons and land application sites can minimize VOC emissions.
View a report on Treasure Valley Air Quality Issues: Ammonia, Particulate, and VOC Emissions (DEQ Publication, February 2003: pdf 57 kb, 10 pages)
We’ll see more on emissions in Idaho and Alaska later.

17. What are the Key Source Types Emitting PM2
What are the Key Source Types Emitting PM2.5 and Its Precursors (Nationally)?
19,976
14,714
18,711
4,143
5,536
TOTAL
3,970
135
211
3,539
3,256
MISCELLANEOUS
2,858
516
4,403 3
292
OFF-HIGHWAY
4,078
145
6,407
307
127
HIGHWAY VEHICLES
395 26
111
268
WASTE DISPOSAL & RECYCLING
1,484 5 19 1 23
STORAGE & TRANSPORT
4,278 7
SOLVENT UTILIZATION
442
327
429
177
354
OTHER INDUSTRIAL PROCESSES
601
257 18
PETROLEUM & RELATED INDUSTRIES 46
213 69 54
METALS PROCESSING
249
259 70 30
CHEMICAL & ALLIED PRODUCT MFG
1,375
578
733 17
421
FUEL COMB. OTHER
152
1,784
2,042
178
FUEL COMB. INDUSTRIAL 48
10,469
3,856 27
508
FUEL COMB. ELEC. UTIL.
VOC
SO2
NOx
NH3
PM2.5
Source Category
2005 Nat’l Emissions (1000 short tons)
Now, lets take a quick look at the national inventory for PM-2.5 and its precursors.
In this chart the main sources in each category are highlighted in red font.
Nationally,
National data indicate that in 2005, PM-2.5 emissions are about 5.5 million tons a year.
Precursors combined emissions are 10 times that many tons as primary PM-2.5
But, only a small fraction of the precursor gases are converted into particles!
Electric utility and industrial boilers are key sources of NOx and SO2,
but mobile sources also emit much NOx.
Mobile sources also emit much of the VOC,
but VOC is also emitted by solvent evaporation.
The Miscellaneous category is very important for PM-2.5, Ammonia and VOC.
What are these miscellaneous sources?
. For PM, it fugitive dust and biomass fires
For ammonia, its animal waste and fertilizer
For VOC, its biomass fires

18. 2005 Emissions in Alaska * Wildland Fires not included 2,616 7,555
PM2.5
VOC
NOx
SO2
NH3
Point
2,616
7,555
78,764
8,622
747
Nonpoint *
11,994
15,449
7,494
5,446
105
Nonroad
7,539
22,485
103,983
53,402 10
Onroad
244
10,382
13,230
407
512
* Wildland Fires not included

19. 2005 Fugitive Dust Emissions in Alaska
STATE
Ag. Crop Tilling
Unpaved Roads
Paved Roads
Construction
ALASKA
7,081
235
535
US Total
535,993
840,556
122,436
199,255

20. 2005 Combustion Emissions in Alaska
Wild
Land
Fires
(2002)
Ag Field
Burning
Res.
Waste
Open
Clearing
Debris
Res. Wood Comb.
ALASKA
672,300 NA
646
1,745 US
1,131,200
224,682
133,639
114,383
381,781

21. Let Us Talk More About Crustal and Carbon
Now we’ll discuss crustal and carbonaceous particles.
Recall that Carbon particles are usually a combination of primary and secondary whereas crustal is a primary particle.
Also, recall that crustal material mainly comes from fugitive dust.

22. Crustal Material – Sources & Composition
Fugitive Dust ~ Main source of Crustal
Unpaved roads
Anti-skid materials on paved roads
Agricultural tilling, dairies
Wind-blown dust
Construction
Fly ash
Composition of Fugitive Dust ~ a mixture of:
“earth oxides” (e.g., oxides of Ca, Al, Si, Fe & Ti)
carbonaceous material (EC, OCM)
The main sources of fugitive dust are unpaved roads, agricultural tilling, construction, and wind-blown dust, which primarily occurs in the arid areas of the western United States.
A less significant source of crustal material is fly ash from coal- or oil-fired boilers, which is chemically similar to crustal material.
Composition is a combination of earth oxides AND carbonaceous material

23. Crustal% = C1Al% + C2Ca% + C3Si% +C4Fe% + C5Ti%
Speciation of Crustal
“Speciation” ~ process of estimating the components of the sample, e.g., crustal by using the chemical characteristics of the sample:
Crustal% = C1Al% + C2Ca% + C3Si% +C4Fe% + C5Ti%
where Al%, Ca%, Si%, Fe% & Ti% are these species % of the sample’s mass
Speciation can be done on both ambient measurements AND emissions
More about emissions speciation later
Speciation is a term we use to describe the process of estimating the Crustal and carbon
This formula is based on the average chemical composition of the oxides in the earth’s crust
So far we have only discussed ambient sample speciation. Speciation is also done routinely on emissions data for use in AQ models.

24. Carbonaceous Material – “Matter”
Ratio of OC to EC differs by source type
Mobile Sources Gas:
Mobile Sources Diesel: 0.4
Open Fires:
Residential Wood Burning:
Fugitive Dust:
Now lets look at carbonaceous matter.
Smoke from fires near
Fairbanks obscures
visibility
LizMarie 2009

25. Organic Carbon “Matter” (OCM) Emissions
“Matter” is the O and H that are part of the OC molecule
The OC measurement must be “augmented” to account for the “matter”
Augmentation of Primary (Fresh) Emissions
augmentation done using a multiplier –
OCM = CEm * OC-Pri
CEm = 1.2 to 1.8 (depending on source type)
CEm applied in Emissions processor
*CEm values documented in Reff 2009
Augmenting Aged Aerosol
CAm = (depends on time, other factors)
Organic carbon reported from analysis of a source or ambient sample does not include the oxygens, hydrogens and other elements that comprise the organic carbonaceous “matter”.
Organic carbon matter includes both primary and secondary organic aerosol.
To approximate the amount of oxygen and hydrogen found in OC emissions use the formula:
OCM = OC x (1.2 to 1.8)
Where CE depends on the source type.

26. Organic Carbon “Matter” (OCM) Emissions
Aerosol Aging and Secondary Formation:
2 aging / formation processes:
1st – particles oxidize as they “age”
2nd – additional “secondary” particles form
AQ Models age the aerosols and account for the formation of secondary organic carbon
In ambient aerosols, the CAm can be as high as 2.4
ambient OC includes secondary formation (which has a high matter content) and
aerosol aging by oxidation, which adds O and H “matter”
2 processes “make” secondary mass
Aging (further oxidation) adds “matter” to existing OC
Secondary particle formation from precursor gases ~ adds OC and M
Since particles in the atmosphere “age” through oxidation and additional OC forms, the overall C in an ambient sample can be as high as 2.4
Recall, we expect to see substantial secondary OC in Fairbanks as well under conditions of summertime wildfire smoke incursions.

27. More About Secondary Formation
Now we’ll discuss crustal and carbonaceous particles.
Recall that Carbon particles are usually a combination of primary and secondary whereas crustal is a primary particle.
Also, recall that crustal material mainly comes from fugitive dust.

28. Precursor Interactions are Important to Particle Formation
(NH4)2SO4
& Particles
Some of this information is a review and other parts are presented here for the first time. Remember, the interrelationships of the formation of Ozone, secondary OC, nitrate and sulfate are very complex.
Its presented here as general background for understanding how precursors interrelate in the formation of secondary PM2.5
Its not simply a matter of reducing ammonia to reduce nitrate
Researchers and chemical transport and transformation modelers struggle with these concepts
Secondary organics:
form from terpenes associated with VOC biogenic emissions (vegetation) occurs quickly
form from aromatics associated with VOC mobile source emissions occurs slower than the terpene reaction
reducing aromatics can reduce S-OC levels
Ammonium sulfate:
forms from SO2 emitted from the combustion of sulfur containing fuels
forms and deposits slower than ozone
can be transported much longer distances than either ozone or nitrate
insufficient ammonia produces partially neutralized particles of ammonium bisulfate, or possibly sulfuric acid
Ammonium nitrate:
forms relatively quickly from NOx emissions from fuel combustion
insufficient ammonia reacts to form ammonium sulfate before forming ammonium nitrate
higher temperatures and a lower relative humidity result in formation of less nitrate and more nitric acid
outcomes are complicated, involve ozone chemistry and can not be generalized
Availability of NOx vs. NH3 may give clue as to what would happen if say NOx Vs NH3 were reduced in a particular airshed, esp. if there is very little SO4 vs. NH4NO3
In conclusion, a reduction in VOC emissions would reduce ozone levels, which would usually result in less secondary organic aerosols, sulfate and nitrate formation.
The complex interactions among ozone formation, ozone precursors, sulfates, nitrates, and secondary organics must be collectively considered.
You must understand the emissions of all precursors in order to be able to understand the effects of emission reductions on secondary PM-2.5 formation.
NH4NO3

29. PM2.5 In Ambient Air - A Complex Mixture
Review:
PM2.5 In Ambient Air - A Complex Mixture
This graphic illustrates the difference between primary, or directly-emitted particles and secondary particles, which are formed in the atmosphere from precursor gases.
Primary particles contain:
elemental carbon (EC)
primary organic aerosol (POA)
small amounts of crustal matter and other materials.
Secondary particles contain:
secondary organic aerosol (SOA) formed from volatile organic compounds
ammonium sulfate formed from SO2 and ammonia gases
ammonium nitrate, formed from NOx and ammonia gases.
The term total carbonaceous matter is used to describe the combined mass of EC, POA, and SOA.
NH4NO3

30. Let Us Review and Summarize
A Complex Mixture
Speciated Ambient Data
Composition
Primary vs. Secondary
Key Sources
Composition by source type
Directly emitted vs. precursors
As we’ve said PM-2.5 is a complex mixture.
There are precursor inter-relationships that makes understanding the precursor-particle formation relationships difficult.
Key sources of both primary emissions and precursor gases must be identified and these should receive special attention in the EI.
The composition and temporal patterns in the composition can help identify these key sources.

31. Review of Important PM2.5 Source Categories
Combustion
a, b
Open Burning (all types)
Non-Road & On-Road Mobile
Residential Wood Burning
Wildfires
Power Gen
Boilers (Oil, Gas, Coal)
Boilers (Wood)
Crustal / Metals b
Fugitive Dust
Mineral Prod Ind
Ferrous Metals
SO2 c
Power Gen (Coal)
Boilers (Coal)
Power Gen (Oil)
Boilers (Oil)
Industrial Processes
NOx
On-Road Mobile (Gas, Diesel)
Non-Road Mobile (Diesel)
Boilers (Gas, Coal)
Residential (Gas, Oil)
NH3
On-Road Mobile
Animal Husbandry
Fertilizer Application
Wastewater Treatment
Boilers
VOC d
Biogenics
Solvent use
On-Road (Gas)
Storage and Transport
Residential Wood
Petrochemical Industry
Waste Disposal
DIRECT EMISSIONS a
Includes primary organic particles, elemental carbon and condensible organic particles; also some flyash
Impact of carbonaceous emissions on ambient PM 5 to 10 times more than crustal emissions impact
Includes SO 2
, and SO 3
and H SO 4
condensible inorganics
Contributes to formation of secondary organic aerosols
PRECURSOR EMISSIONS
NOTE:
Categories in
BOLD
are most important nationally. Their
relative importance varies among and
between urban and rural areas.
This chart summarizes the larger source categories of PM2.5 direct and precursor emissions.

32. Questions?
Wonderlane 2008
Wonderlane 2008