Ozone and Particulate Matter


Ozone (O3) is a highly oxidative molecule found in the air. When it forms high in the stratosphere, O3 is critical to life on Earth because it absorbs harmful ultraviolet radiation from the sun. But in the low atmosphere (troposphere) or at ground level, O3 is considered a health hazard. Tropospheric O3 is produced by sunlight-induced photochemical processes involving nitrogen oxides (NOx) and volatile organic compounds (VOCs). These precursor gases are derived from natural and anthropogenic (man-made) sources. Ozone concentrations are generally highest in and around urban areas.

Particulate Matter (PM) refers to tiny airborne particles that originate from various natural and anthropogenic sources, some of which are produced from chemical reactions of sulfur dioxide (SO2), NOx and certain VOCs. They are composed of many compounds rather than one substance, also referred to as dust, haze, and smoke. PM is regulated in two categories of particle size: particles that are less than 10 micrometers (µ) in diameter (PM10), and "fine" particles of less than 2.5µ in diameter (PM2.5).

Human Health and Environmental Effects and Regulation

Both ozone and PM have a negative effect on human health and the environment. Ozone is identified with adverse human health impacts, including respiratory stress such as asthma. The environmental effects of PM include reduced visibility, acid deposition, damage to crops and forests, and increased corrosion of materials. Adverse health effects of PM, especially the smaller PM2.5, include reduced lung function growth, as well as respiratory and cardiac disease and mortality. Children, the elderly, diabetics and those with underlying heart or lung disease are most susceptible.

The EPA has regulated ozone and PM as criteria pollutants since 1970 under the federal Clean Air Act (CAA) and New York State environmental regulations. Under the CAA, each state is required to submit a State Implementation Plan (SIP) to the EPA to meet National Ambient Air Quality Standards (NAAQS) for both O3 and for PM2.5. New York's SIP is scheduled to be submitted for approval by 2007. The CAA regulations have resulted in substantial reductions in emissions of O3 and PM, as well as secondary PM precursor gases. Despite these legal provisions, in 2002, 136 million people in the U.S. lived in counties that violated ozone standards, and 59 million people lived in counties where PM2.5 standards were exceeded.

Conditions in New York State

In general, concentrations of O3 and PM2.5 in New York State tend to be higher than in other regions of the country. This is partly due to the state's large metropolitan population and high level of industrialization. However, it is also due to an important atmospheric phenomenon identified as the long-range transport of pollutants, which involves the movement of pollution from out-of-state sources into New York via the prevailing winds. Long-range transport studies have shown that, under typical meteorological conditions, SO2, NOx, and O3 travel to New York State from large industrial and energy generation sources in the Midwest and the mid-Atlantic region.

The primary anthropogenic source of O3 precursor gases is fuel combustion. The largest sources of NOx, for example, are associated with transportation and electric power generation. Other sources of concern include industrial and commercial operations, as well as residential fuel use. Emissions of VOCs are identified with mobile sources and internal combustion engines, but industrial sources such as oil refineries and chemical plants, as well as commercial and residential activity, are also of concern.

Sources of PM differ between coarse and fine particles. Coarse PM generally includes windblown and road dust, sea spray, and biological material including bacteria, fungi and detritus. Fine particles are distinct in that their primary sources are identified with fuel combustion (including internal combustion engines), and industrial, commercial and residential heaters, as well as wood burning and vegetation fires. The sources of secondary fine particles (those formed from the cooling or reacting of gases in the atmosphere rather than directly emitted from a source) involving SO2, NOx, VOCs and ammonia (NH3) come from many different sources, most of which are identified with the O3 sources.

New York State has established 30 ozone monitoring sites that cover both urban centers and surrounding rural areas, and 39 sites for monitoring PM2.5. Ozone and PM precursor gases also are being measured at a few locations, and electricity-generating stations are required to report levels of NOx and SO2 in their smokestack emissions. Motor vehicles are checked for VOC and NOx emissions when they leave the assembly line, and on-road motor vehicles are periodically sampled for emissions. Through these efforts, a long-term picture of air quality change has emerged. Results have shown reductions in O3 and precursor gases that can be attributed to emissions reductions. PM10 concentrations have also declined across the U.S. in response to emission controls.

Perhaps the most important measure of air quality is the link to human health, although changes in human health resulting from air quality improvements are very difficult to measure because they are also affected by other risk factors such as smoking, weather, access to healthcare, and socio-economic factors. Determining the relative influence of these various factors on human health has been difficult. However, community health and toxicological studies of O3 exposure indicate that people experience less respiratory stress when levels of O3 in the air are low, than when O3 levels exceed standards. The long-term effects of O3 exposure have not been documented.

Research Implications

The public has continued to show its strong support for cleaner air in the United States and New York State in particular. In addition to regulatory programs, several federal and state agencies including EPA, NYSDEC, and NYSERDA are supporting voluntary emission reduction initiatives. These programs include clean transit bus and school bus programs, diesel idle reduction programs, emission reduction efforts in the marine sector, and cleaner fuel oil for heating. The state is also pursuing reduced vehicle emissions, through lower-emissions engines, ultra-low sulfur fuel, and pollution control devices. Regional initiatives and interstate planning are addressing the long-range transport of emissions.

Primer on Ozone and Particulate Matter [PDF], prepared by NYSERDA, provides a more detailed overview of O3 and its effects on human health and the environment, and a summary of research findings in New York and the Northeast.

Last Updated: 06/03/2014