Report on the Environment
Particulate Matter Emissions
What are the trends in outdoor air quality and their effects on human health and the environment?
The above question pertains to all 'Outdoor Air' Indicators, however, the information on these pages (overview, graphics, references and metadata) relates specifically to "Particulate Matter Emissions". Use the right side drop list to view the other related indicators on this question.
- Avoid spilling gasoline, and don't "top off" the tank.
- Check daily air quality forecasts
- Use paints, stains, finishes, and paint strippers that are water-based or low in volatile organic compounds.
- On ozone action days, refuel your vehicle after dusk.
- Avoid burning leaves, trash, and other materials that cause particle pollution when incinerated.
- Acid Deposition
- Air Toxics Emissions
- Ambient Concentrations of Benzene
- Ambient Concentrations of Carbon Monoxide
- Ambient Concentrations of Lead
- Ambient Concentrations of Manganese Compounds in EPA Region 5
- Ambient Concentrations of Nitrogen Dioxide
- Ambient Concentrations of Ozone
- Ambient Concentrations of Particulate Matter
- Carbon Monoxide Emissions
- Concentrations of Ozone-Depleting Substances
- Lake and Stream Acidity
- Lead Emissions
- Mercury Emissions
- Nitrogen Oxides Emissions
- Ozone Injury to Forest Plants
- Ozone Levels over North America
- Ozone and Particulate Matter Concentrations for U.S. Counties in the U.S./Mexico Border Region
- Particulate Matter Emissions
- Percent of Days with Air Quality Index Values Greater Than 100
- Regional Haze
- Sulfur Dioxide Emissions
- Volatile Organic Compounds Emissions
Click to enlarge exhibit
“Particulate matter” (PM) is the general term used to describe solid particles and liquid droplets found in the air. The composition and size of these airborne particles and droplets vary. Some particles are large enough to be seen as dust or dirt, while others are so small they can only be seen using a powerful microscope. Two size ranges, known as PM10 and PM2.5, are widely monitored, both at major emissions sources and in ambient air. PM10 includes particles that have aerodynamic diameters less than or equal to 10 microns (µm), approximately equal to one-seventh the diameter of human hair. PM2.5 is the subset of PM10 particles that have aerodynamic diameters less than or equal to 2.5 µm.
Particles within the two size ranges behave differently in the atmosphere. PM2.5, or fine particles, can remain airborne for long periods and travel hundreds of miles. Coarse particles, or the subset of PM10 that is larger than 2.5 µm, do not remain airborne as long and their spatial impact is typically limited because they tend to deposit on the ground downwind of emissions sources. Larger coarse particles are not readily transported across urban or broader areas because they are generally too large to follow air streams and they tend to be removed easily on contact with surfaces. In short, as the particle size increases, the amount of time the particles remain airborne decreases. The PM Concentrations indicator describes the various ways PM can harm human health and the environment (U.S. EPA, 2004).
PM can be emitted directly or formed in the atmosphere. “Primary” particles are those released directly to the atmosphere. These include dust from roads and soot from combustion sources. In general, coarse PM is composed largely of primary particles. “Secondary” particles, on the other hand, are formed in the atmosphere from chemical reactions involving primary gaseous emissions. Thus, these particles can form at locations distant from the sources that release the precursor gases. Examples include sulfates formed from sulfur dioxide emissions from power plants and industrial facilities and nitrates formed from nitrogen oxides released from power plants, mobile sources, and other combustion sources. Unlike coarse PM, a much greater portion of fine PM (PM2.5) contains secondary particles (U.S. EPA, 2004).
This indicator presents trends in annual average primary PM emissions data tracked by the National Emissions Inventory (NEI). The NEI tracks emission rate data, both measured and estimated, for primary particles only. Because secondary particles are not released directly from stacks, the NEI instead tracks the precursors that contribute to formation of secondary particles. These precursors include nitrogen oxides, sulfur dioxide, ammonia, and other gases (e.g., particle-producing organic gases), some of which are addressed in separate indicators (the Nitrogen Oxides Emissions indicator; the Sulfur Dioxide Emissions indicator). Particles formed through secondary processes are not included in this indicator.
Primary emissions of PM can exist as solid or liquid matter (the “filterable” portion) or as gases (the “condensable” portion). Data for the condensable portion exist only for the years 1999 to 2005. To allow for a valid comparison of emissions trends from 1990 to 2005, only data for the filterable portion of PM10 and PM2.5are included in the trend graphs. Condensables are, however, included in the inset pie charts shown in Exhibits 2-16 and 2-18 (i.e., panel B in both exhibits).
All emissions data presented in this indicator are taken from the NEI. Primary particulate emissions data are presented for the traditionally inventoried anthropogenic source categories: (1) “Fuel combustion,” which includes emissions from coal-, gas-, and oil-fired power plants and industrial, commercial, and institutional sources, as well as residential heaters and boilers; (2) “Other industrial processes,” which includes chemical production, petroleum refining, metals production, and processes other than fuel combustion; (3) “On-road vehicles,” which includes cars, trucks, buses, and motorcycles; and (4) “Nonroad vehicles and engines,” such as farm and construction equipment, lawnmowers, chainsaws, boats, ships, snowmobiles, aircraft, and others. For 2005 only, this indicator includes a comparison of these anthropogenic sources with emissions from miscellaneous and natural sources, such as agriculture and forestry, wildfires and managed burning, and fugitive dust from paved and unpaved roads. Biogenic emissions were estimated using the Biogenic Emissions Inventory System Model, Version 3.12, with data from the Biogenic Emissions Landcover Database and 2001 annual meteorological data. The NEI also documents estimates of primary emissions from fugitive dust and miscellaneous sources.
The NEI is a composite of data from many different sources, including industry and numerous state, tribal, and local agencies. Different data sources use different data collection methods, and many of the emissions data are based on estimates rather than actual measurements. For most fuel combustion sources and industrial sources, emissions are estimated using emission factors. Emissions from on-road and nonroad sources were estimated using EPA-approved modeling approaches (U.S. EPA, 2008).
NEI data have been collected since 1990 and cover all 50 states and their counties, D.C., the U.S. territories of Puerto Rico and Virgin Islands, and some of the territories of federally recognized American Indian nations. Data are presented for 1990, from 1996 to 2002, and for 2005. Data are available from 1991 to 1995 and from 2003 to 2004, but these data have not been updated to be comparable to the inventories from 1990, 1996 to 2002, and 2005.
Primary PM 10 Emissions Trends
Estimated primary PM10 emissions from anthropogenic sources decreased 33 percent nationally between 1990 and 2005 (Exhibit 2-16, panel A). Of these sources, those in the fuel combustion category saw the largest absolute and relative decrease in emissions (704,000 tons; 59 percent). Primary PM10 emissions from the group of sources including miscellaneous and natural sources and fugitive dust were estimated to account for 88 percent of total primary PM10 emissions (including condensables from stationary and mobile sources) in 2005, the majority of which was attributable to fugitive dust from roads (Exhibit 2-16, panel B).
Changes in estimated primary anthropogenic PM10 emissions from 1990 to 2005 varied widely among EPA Regions, ranging from an increase of 4 percent (Region 8) to a decrease of 78 percent (Region 2) (Exhibit 2-17).
Primary PM2.5 Emissions Trends
Estimated primary PM2.5 emissions from anthropogenic sources decreased 48 percent nationally between 1990 and 2005 (Exhibit 2-18, panel A). The largest absolute and relative decline in PM2.5 was seen in the fuel combustion source category (647,000 tons; 71 percent). Primary emissions from the group of sources including miscellaneous and natural sources and fugitive dust were estimated to account for 60 percent of the total PM2.5 emissions (including condensables from stationary and mobile sources) nationally in 2005 (Exhibit 2-18, panel B).
Primary anthropogenic PM2.5 emissions decreased in all ten EPA Regions from 1990 to 2005, with percent reductions ranging from 19 percent (Region 9) to 76 percent (Regions 1 and 2) (Exhibit 2-19).
- Comparable PM emissions estimates through the NEI are available only for 1990, 1996-2002, and 2005. Data for 1991-1995 and 2003-2004 are not provided due to differences in emissions estimation methodologies from other inventory years, which could lead to improper trend assessments.
- Because the emissions indicators focus on sources of anthropogenic origin, PM emissions from miscellaneous sources (e.g., wildfires) are not included in the trend line. Details on emissions from these sources can be found by downloading NEI inventory data for the “nonpoint sector” (http://www.epa.gov/ttn/chief/eiinformation.html).
- The emissions data for PM are largely based on estimates that employ emission factors generated from empirical and engineering studies, rather than on actual measurements of PM emissions. Although these estimates are generated using well-established approaches, the estimates have uncertainties inherent in the emission factors and emissions models used to represent sources for which emissions have not been directly measured.
- The methodology for estimating emissions is continually reviewed and is subject to revision. Trend data prior to these revisions must be considered in the context of those changes.
- The indicator tracks primary PM emissions. Particles that form in the air through secondary processes are not included in this indicator, but are considered in the PM Concentrations indicator.
- Not all states and local agencies provide the same data or level of detail for a given year.
Summary data in this indicator were provided by EPAs Office of Air Quality Planning and Standards, based on biogenic and anthropogenic particulate matter emissions data in the NEI. The most recent data are taken from Version 2.0 of the 2005 NEI (U.S. EPA, 2009). These and earlier emissions data can be accessed from EPAs emission inventory Web site (http://www.epa.gov/ttn/chief/eiinformation.html). This indicator aggregates NEI data by source type (anthropogenic or biogenic), source category, and EPA Region.
U.S. EPA (United States Environmental Protection Agency). 2009. Data from the National Emissions Inventory, Version 2.0. Accessed 2009. http://www.epa.gov/ttn/chief/eiinformation.html
U.S. EPA. 2008. Documentation for the final 2005 mobile National Emissions Inventory, Version 2. ftp://ftp.epa.gov/EmisInventory/2005_nei/mobile/2005_mobile_nei_version_2_report.pdf
U.S. EPA. 2004. Air quality criteria for particulate matter (October 2004). EPA 600/P-99/002aF-bF. Research Triangle Park, NC. http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=87903
|Particulate Matter Emissions|
|2.||ROE Question(s) This Indicator Helps to Answer|
|This indicator is used to help answer one ROE question: "What are the trends in outdoor air quality and their effects on human health and the environment?"|
This indicator presents regional and national particulate matter (PM) emissions data for 1990, 1996 to 2002, and 2005. Data are presented for two different PM size fractions. PM emissions (combined with atmospheric fate and transport processes) determine corresponding ambient PM concentration levels.
The emissions data for this indicator come from EPA's National Emissions Inventory (NEI). The NEI is a composite of data from many different sources, including industry and numerous state, tribal, and local agencies.
Summary data in this indicator were provided by EPA's Office of Air Quality Planning and Standards, based on PM emissions data in EPA's NEI. EPA makes the complete underlying data set (i.e., the NEI) and all data dictionaries available through its Web site named, "Clearinghouse for Inventories and Emission Factors" (CHIEF). Summary data in this indicator were provided by EPA's Office of Air Quality Planning and Standards, based on raw PM emissions data in EPA's NEI (2005 data: http://www.epa.gov/ttn/chief/net/2002inventory.html; 2002 data: http://www.epa.gov/ttn/chief/net/2002inventory.html; pre-2002 data: http://www.epa.gov/ttn/chief/net/critsummary.html). This indicator aggregates the raw NEI data by source type (i.e., anthropogenic or biogenic), source category, and EPA Region. The trend lines shown in the indicator track changes in only filterable PM emissions, because condensable PM emissions data are not available dating back to 1990.
The particulate matter (PM) emissions data in NEI are based almost entirely on emissions estimates, not direct measurements.
Mobile sources include PM emissions from on-road vehicles (i.e., cars, trucks, buses, and motorcycles) and nonroad vehicles and engines (e.g., farm and construction equipment, lawnmowers, chainsaws, boats, ships, snowmobiles, aircraft). Emissions from on-road mobile sources are estimated using EPA's MOBILE emissions model, with input data on vehicle miles traveled based on estimates provided by the Federal Highway Administration. Emissions from nonroad mobile sources are estimated using EPA’s NONROAD emissions model. Both the MOBILE and NONROAD emissions models are considered to be scientifically and technically valid, and many aspects of both models have been subject to external, independent peer review. See "Data Sources" for documentation on these emissions models.
Point sources include fuel combustion sources (i.e., coal-, gas-, and oil-fired power plants and industrial, commercial, and institutional sources, as well as residential heaters and boilers) and other industrial processes (i.e., chemical production, petroleum refining, metals production, and processes other than fuel combustion). Emissions from point sources are primarily estimates, generated by using emission factors, models, or other estimation methodologies. Though the estimated emission rates have inherent uncertainties, the approaches used to estimate these emissions are well documented (e.g., in U.S. EPA, 2004), widely accepted as technically valid, and have been peer reviewed. Moreover, efforts are made to update and improve the estimation methodologies periodically (U.S. EPA, 2007a).
The PM emissions data in NEI cover particles of two different size fractions (PM10 and PM2.5) and physical state (filterable and condensable). PM10 includes particles that have aerodynamic diameters less than or equal to 10 microns (µm), and PM2.5 is the subset of PM10 particles that have aerodynamic diameters less than or equal to 2.5 µm. Filterable PM refers to particles or droplets that can be collected on filters in the stack exhaust; condensable PM exists in the vapor phase in the stack, but readily condenses into particulate (liquid) form upon being released from the stack and exposed to ambient conditions. Starting in 1999, the NEI began tracking condensable PM separate from filterable PM. The primary trends tracked in this indicator are for filterable PM10 emissions and filterable PM2.5 emissions; nationwide data for emissions of condensable PM have only recently become available and are not included in this indicator unless otherwise specified.
The NEI is a composite of data from many different sources. State and local agencies and other parties provide much of the data to EPA. Although these original data are accompanied with little or no documentation on the specific methods used to estimate emissions, state and local agencies and other parties generally follow procedures documented in an emission inventory guidebook on acceptable methods for estimating emissions (U.S. EPA, 2007c). See U.S. EPA (2007a and 2007b) for further information on approaches commonly taken to estimate air emissions from various sources. Once received, EPA processes the emissions data according to procedures outlined in the NEI Preparation Plan (e.g., U.S. EPA, 2004). Taken together, these references describe the preferred approaches that state and local agencies and other parties follow to generate PM emissions data and the approach EPA takes to compile and organize these data.
In some cases, the data provided by state and local agencies and other parties are absent or incomplete. When this occurs, EPA fills the gaps using various data extrapolation methods, such as using data from previous years or inferring data for a given county based on data from other counties believed to have common properties that influence emissions (e.g., population density, daily low and high temperatures). Steps taken to fill these data gaps have been applied consistently over the years and have been subject to independent peer review.
NEI emissions data for filterable PM are available for 1990, 1996 to 2002, and 2005 using a consistent methodology. Emissions data in the inventory cover all 50 states, the District of Columbia, Puerto Rico, and the U.S. Virgin Islands. Thus, NEI data are meant to capture an estimate of all PM emissions released in the U.S. The NEI characterizes emissions sources, not human populations or ecosystems. Therefore, the concept of "sensitive populations or ecosystems" does not apply to this indicator. It should be noted that NEI data do provide insights on emissions sources throughout the country, including localized areas that might be near sensitive populations or ecosystems, though the focus of this indicator is on regional and national trends.
The indicator describes nationwide and regional PM emissions for 1990, 1996 to 2002, and 2005. Data were not extrapolated beyond the scope of data collection, and no statistical generalization was performed to generate the regional and national emissions trends presented in this indicator. The regional trends were computed by totaling all emissions data for individual facilities and counties within the corresponding EPA Region for the specific inventory years. Similarly, national data represent totals across all states and territories considered in the inventory.
While the NEI database is composed of tens of thousands of emissions estimates or measurements from dozens of state and local agencies and other parties, key aspects of NEI development and implementation are subject to independent peer review to ensure that the data are scientifically sound and technically accurate. Though reproducing the entire NEI database would be difficult, reproducing the PM emissions data that this indicator reports for different EPA Regions and different source categories is more straightforward. This can be accomplished by first downloading the entire database of PM emissions (which can be accessed as text files from the links documented in "Data Availability"). The indicator data can then be verified by importing the text files into some type of database or spreadsheet software and then running queries to verify the national and regional totals.
|9.||Quality Assurance and Quality Control|
The data in the NEI are gathered from numerous sources. Though the quality of the original data submitted to EPA can vary, several quality assurance (QA) and quality control (QC) measures are in place to ensure that data of acceptable quality enters the inventory and is processed correctly. It is presumed that state agencies supplying emissions data have QA plans, but EPA does not systematically obtain information on QA practices from the states. The EPA contractors who support the Agency on inventory development operate under general contract-wide QA plans, which can be made available on request. In addition, EPA's more recent QC practices performed during the blending and merging of data from numerous sources are publicly available (U.S. EPA, 2007a).
The concepts of reference points, thresholds, and ranges of values "that unambiguously reflect the state of the environment" do not really apply to emissions indicators. There are no thresholds or ranges of values associated with "safe" levels of PM emissions across an entire region or nation. The air quality impacts associated with a given regional or national emissions total depend on the distribution of emissions among individual sources and the release parameters (e.g., stack heights, exit velocities) at these sources. Emissions data can provide general insights on air quality trends, but cannot be used alone to gauge "the state of the environment" (i.e., ambient air concentrations of PM). The indicator on ambient PM concentrations, however, provides more direct insights on the state of the environment.
|11.||Comparability Over Time and Space|
NEI data have been collected since 1990. Data are presented for those years (i.e., 1990, 1996 to 2002, and 2005) in which NEI data have been fully updated using consistent methodologies. Assuming the providers of the data abide by these consistent estimation methodologies, the emissions data should be reasonably comparable over both time and space.
|12.||Sources of Uncertainty|
Content under review.
|13.||Sources of Variability|
The decrease in nationwide PM emissions between 1990 and 2005 resulted from reductions in emissions from multiple source categories. Variability in PM emissions from specific sources (and source categories) results from many factors. Average precipitation amounts and wind speeds, for instance, affect the variability in emissions of wind-blown dust. These and other sources of variability are explicitly accounted for in the emissions estimation approaches, to the extent that the underlying algorithms account for them.
This indicator presents a time series of regional and national emissions estimates. No special statistical techniques or analyses were used to characterize the long-term trends or their statistical significance.
Limitations to this indicator include the following:
U.S. EPA (United States Environmental Protection Agency). 2007a. Emission Inventory Improvement Program technical report series. Volumes 1-10. Updated October 18, 2007. http://www.epa.gov/ttn/chief/eiip/techreport/.
U.S. EPA. 2007b. Clearinghouse for inventories and emissions factors. http://www.epa.gov/ttn/chief/.
U.S. EPA. 2007c. What is the Emission Inventory Improvement Program (EIIP)? http://www.epa.gov/ttn/chief/eiip/whatis.html.
U.S. EPA. 2004. 2002 National Emission Inventory (NEI) preparation plan. Final report, August. ftp://ftp.epa.gov/EmisInventory/2002finalnei/general_information/2002neiplan_081004final.pdf (89 pp, 232K, About PDF).
U.S. EPA. 1996. Evaluating the uncertainty of emission estimates. Volume VI: Chapter 4. July, 1996. http://www.epa.gov/ttn/chief/eiip/techreport/volume06/vi04.pdf (55 pp, 304K).