Objectives and History
Objectives and History
|National PEP Weighing Laboratory
US-EPA, Region 4
Science and Ecosystem Support Division
What is PM2.5
Particulate matter is the term used for a mixture of solid particles and liquid droplets found in the air. PM2.5 refers to particulate matter that is 2.5 micrometers or smaller in size. 2.5 micrometers is approximately 1/30 the size of a human hair; so small that several thousand of them could fit on the period at the end of this sentence. The sources of PM2.5 include fuel combustion from automobiles, power plants, wood burning, industrial processes, and diesel powered vehicles such as buses and trucks. These fine particles are also formed in the atmosphere when gases such as sulfur dioxide, nitrogen oxides, and volatile organic compounds (all of which are also products of fuel combustion) are transformed in the air by chemical reactions. Fine particles are of concern because they are risk to both human health and the environment.
Because these particles are so small they are able to penetrate to the deepest parts of the lungs. Scientific studies have suggested links between fine particulate matter and numerous health problems including asthma, bronchitis, acute and chronic respiratory symptoms such as shortness of breath and painful breathing, and premature deaths. Most of these premature deaths are the elderly who's immune systems are weaker due to age or other health problems such as cardiopulmonary diseases.
Children are more susceptible to the health risks of PM2.5 because their immune and respiratory systems are still developing. The average adult breaths 13,000 liters of air per day and children breath up to 50 percent more air per pound of body weight than adults. The breathing of fine particles by children is believed to cause both acute and chronic respiratory problems such as asthma. Forty percent of all asthma cases are children who make up only 25 percent of the population.
These same fine particles that lead to health effects are also a major cause of visibility impairment in most parts of the United States. It is estimated that in certain parts of the U.S. the visual range has been reduced by 70% of natural conditions. Because these particles are so small they can travel great distances affecting areas in other states or even regions. It is believed that one-third of the haze seen over the Grand Canyon comes from Southern California.
These fine particles also have a great affinity for water thus contributing to acid rain. Acid rain affects all things biological or man made and by thus affecting the environment, can have repercussions to human health. This problematic cycle is why the EPA has taken an initiative to monitor and address fine particles in the atmosphere.
Community-oriented (core) sites that represent community-wide average exposure, form the basis of the PM2.5 network design. The network has close to 1500 sites throughout the US territories that are maintained by both federal, state, and local agencies. The network consists of different elements that serve multiple information needs.
The network elements are as follows:
Making regional comparisons for PM2.5 National Ambient Air Quality Standards (NAAQS) is the prime objective of the PM2.5 network. This comparison is done with mass-only samplers which detect ambient concentrations of PM2.5 over a 24-hour period. Filters are pre-weighed under controlled conditions, run in samplers for 24 hours with a known volume of air, then post-weighed to determine ambient concentrations. At least three years of data will be collected before compliance issues are addressed. All sampling sites that provide data for comparison to either the 24-hour or the annual PM2.5 NAAQS for the purpose of addressing attainment/nonattainment must use federally referenced samplers and techniques.
The US EPA decided that continuous monitoring would be required in each of the nation's 52 largest metropolitan areas or cities. The continuous monitoring of PM2.5 will provide useful data for public reporting of short-term concentrations, for understanding diurnal and episodic behavior of fine particles, and for use by health scientists investigating exposure patterns. In lieu of filters, the samplers use an internal analytical apparatus to instantaneously measure the particles passing through the sampler.
Knowing the chemical composition of the PM2.5 mix is important for determining sources of pollution. The basic objective of the chemical speciation analysis is to develop seasonal and annual chemical characterizations of ambient particulates across the nation. This speciation data will be used to perform source attribution analyses, evaluate emission inventories and air quality models, and support health related research studies and regional haze assessments. The speciation samplers use different inlet tubes and filters to collect suspected harmful components of the PM2.5 mixture.
Prior to the establishment of the PM2.5 network, there existed the IMPROVE (The Interagency Monitoring of Protected Visual Environments) network which is a joint effort of the Department of Interior, Federal Land Managers, and state/local agencies. This network monitored the visibility and chemical compositions of aerosols in remote and rural regions across the US. With the advent of the PM2.5 network, new monitoring sites were combined with the existing network since the monitoring and objectives of both programs were compatible.
Also known as special chemical speciation studies, these sites focus on regional areas with distinct particulate problems. These sites will contain a mixture of complex research-grade machines that will sample for multiple parameters. These "super" sites will give scientist in both agencies and the research arena a more comprehensive information pool to make better decisions regarding particulate monitoring. These sites will help to provide a better understanding of the patterns and chemistry of these pollutants as well as improve on the understanding of their health effects.
Any organization that is collecting and evaluating environmental data must be concerned with the quality of their results. Since data received from the PM2.5 monitoring network will be used by decision makers regarding NAAQS attainment, a quality assurance program was adapted to limit monitoring bias within an acceptable level so that decisions can be made confidently.
One component of the PM2.5 quality assurance plan is the FRM Performance Evaluation Program (PEP) which accompanied the implementation of the PM2.5 FRM network in 1999. This program is designed to determine total bias for the PM2.5 sample collection and laboratory analysis processes. Field contractors for the EPA setup federally referenced samplers that are collocated adjacent to a monitoring site's routine sampler and run for a 24-hour period. The concentrations are then determined independently by EPA laboratories and compared in order to assess bias. Various statistical analyses are conducted between EPA data and state/local data to determine if bias exists. At a minimum, eight or five performance evaluations, depending on network size, are conducted each year at the sampling sites in a reporting organization. All monitoring sites in the network are expected to be audited in a six year period.
In addition to the EPA's performance evaluation, each state and local monitoring agency has permanent collocated samplers at 25% of their sites. These collocated samplers will also rotate each year. The combination of these two quality assurance programs will provide data to measure minimal bias which can be used to address the concerns with fine particles in the atmosphere.
For more information concerning the ambient monitoring data collected and monitoring sites nationwide and locally, check out the websites listed on our PM2.5 links web page.
Note: each of the following photo images link to a larger version of the photograph
Air Monitoring Site
Loading Air Sampler
Changing PM 2.5 Filter
Downloading RUN Data
Comparison of Exposed and Unexposed Filters
BGI PQ200A Air Sampler Control Panel and
BGI, Andersen and R&P Collocation/Comparison
Katrina Particulate Monitoring
R&P Single Channel Sampler
Andersen Single Channel Sampler