The Environmental Protection Agency (EPA) considers fine particle pollution one of its most pressing air quality issues for public health and environmental reasons. Because of the potential contribution construction activities can have on particle pollution, the LMCCC has established a neighborhood-scale ambient air-monitoring program for the monitoring and control of particulate matter.

Comparison of Particulate Matter (PM) Sizes

• Particulate matter is monitored for coarse and fine particulates. Coarse particulates include particles with a diameter less that 10 μm, which is referred to as PM₁₀. Fine particulates include particles less than 2.5 μm in diameter and are referred to as PM_2.5. Some large particles are visible to the human eye, though most can only be seen with a microscope.
  
  

Sources and Emissions

• Particulate matter is composed of solid material and liquid droplets, which can come from mobile and stationary sources. The larger particles usually drop out of the air more quickly than the smaller particles, which can be transported long distances from their sources.
• Particulate matter is composed of a variety of chemical components, which are typically divided into categories of sulfates, nitrates, carbon, and crustal material.
• Some particulate matter is emitted directly into the atmosphere as particles (primary particles), while other particles are produced by chemical reactions in the atmosphere (secondary particles). Generally, coarse particulate matter consists of primary particles, and fine particulate matter is mainly secondary particles.
• Primary emissions typically consist of carbon and crustal sources, which include soot, dust, and dirt emitted by motor vehicle exhausts, burning trash, forest fires, construction sites, stone crushing, and mining operations.
• Secondary emissions form during chemical reactions in the air. Nitrogen oxides and sulfur dioxide emissions from motor vehicles, power plants, and other industrial facilities can react to in the presence of sunlight and water vapor to form nitrates and sulfates. 

Health Issues

• Particulates less than 10 μm in diameter are considered inhalable particulates, which can penetrate the body's natural defenses, getting deep into the respiratory system. The smaller the particle, the further into the lungs it is able to travel.
• Exposure to particle pollution may cause eye, nose, throat, and lung irritation, coughing, sneezing, runny nose, and shortness of breath, with long-term exposure leading to more serious health problems.

Urban Haze

• Visibility impairment, or haze, limits the distance we can see and reduces the color, clarity, and contrast of the view. Urban haze is perhaps the most visible impairment to the notion of "clean-air." Much of haze is caused by the same particles that may contribute to health problems and environmental damage. Haze is typically more of a problem in the eastern United States and during the summer months as humidity can increase the effect of particulate matter, thus worsening the haze.

Seasonal Trends

• Particle pollution varies by time of year, location, and weather conditions. Particulate matter has varying composition among the different regions of the county. Concentrations of fine particulate matter in the Northeast are typically the highest between July and September. Temperature, humidity, wind, and weather patterns affect the concentrations of particulate matter detected in the air.

Rural Versus Urban Particulate Matter Composition

• Particulate matter concentrations and the composition, or actual physical make-up, of the particulate matter, are influenced by local and regional sources. Particulate matter in eastern U.S. cities contains more carbon and nitrates than rural midwestern particulate matter, which contains more crustal matter and pesticides. Regional pollution contributes more than half of the total PM_2.5 composition, but the other half may travel long distances. An example of the latter is the effect power plants in the Ohio Valley have on particulate matter in New York City. Carbon provides the largest percent of the composition and is from a combination of rural and local sources. Nitrates are typically found at higher levels in urban areas, while sulfates tend to be transported from regional sources.

Control Programs (National and Local)

• The EPA established the National Ambient Air Quality Standards (NAAQS) which establish standards for both coarse and fine particulates. The 24-hour average concentration for PM₁₀ is 150 μg/m³ and 35 μg/m³ for PM_2.5. The EPA also set a total annual average for PM_2.5 of 15 μg/m³. While the overall concentration of particulate matter has been decreasing in most eastern cities over recent years, many urban locations are considered non-compliance areas for the NAAQS because of the difficulty meeting the requirement for the annual average for PM_2.5 (15 μg/m³). The EPA recently made the required annual average for PM_2.5 more stringent (it was 35 μg/m³ until 2006) because they want to ensure that the United States continues to reduce PM_2.5 levels in urban areas. 

Monitoring Programs

• There are national and regional monitoring programs throughout the United States. The New York State Department of Environmental Conservation's (NYSDEC's) Ambient Air Quality Monitoring Program includes measuring for particulate matter, among other criteria pollutants. However, for a variety of reasons, not all areas of the country have particulate matter monitoring. In order to improve air quality assessment, management, and prediction, NASA has joined with the EPA and NOAA to combine satellite measurements with current air monitoring programs.
• Historically, particulate matter mass and composition have been monitored using filter-based methods with 24-hour (or longer) averages. Inlets to the sampling systems have traditionally been set with particle diameter cut points of 2.5 or 10 μm (see figure below). The federal reference method (FRM) collects PM onto a specialized filter that is weighed before and after sampling. The EPA has deemed certain types of continuous monitors to be reference method equivalent methods.

• Deployment of continuous PM_2.5 and PM₁₀ monitoring networks began in 1999 and has quickly produced a more detailed understanding of particulate matter pollution and improved our ability to respond to elevated particle pollution levels in real-time. The LMCCC ambient air monitoring network employs continuous monitoring to provide automated alarms in real time to help control particulate matter during the construction currently underway in Lower Manhattan.