The links below also include programs related to topics such as acid rain, global warming, and the hole in the ozone layer. Prevailing winds transport the compounds, sometimes for hundreds of miles, across state and national borders. Before falling to the Earth, SO2 and NOx gases and their particulate matter derivatives, sulfates and nitrates, impair visibility and have an adverse effect on public health. To protect stratospheric ozone, the manufacture of ozone-depleting chemicals is being phased out and restrictions are being placed on their use and distribution. Back to the top Particulates Particulate matter is the term for solid or liquid particles found in the air.
Some particles are large or dark enough to be seen, such as soot or smoke.
Others are so small they can be detected only with an electron microscope. The new standard focuses on smaller particles that are likely responsible for adverse health effects because of their ability to reach the lower regions of the respiratory tract. The elderly, children, and people with chronic lung disease, influenza, or asthma are especially sensitive to the effects of particulate matter. As a result, EPA is considering setting a new standard for PM-2.5. In addition, EPA is reviewing whether revisions to the current PM-10 standards are warranted.