When ozone pollution levels are high, other pollutants can also be present, causing public exposure to multiple pollutants. In the eastern U.S., concentrations of airborne particulate matter tend to be high on the same days that o
zone levels are high. Sometimes, both pollutants are elevated during the same times of the day, though this is not always so.
"Particulate matter" refers to particles of fine dust, soot, pollen, or minute amounts of chemicals condensed or accumulated in the air. In 1995 airborne particulate matter was measured in all the Mid-Atlantic states using PM10 monitors. These monitors measure concentrations of airborne particles with a diameter of 10 microns or less.
The following two charts review concentrations of ozone and particulate matter (PM10) measured at the Aldino Airport in Harford County, Maryland in July 1995. The first chart shows that ozone levels rose sharply from July 9th through the 15th, and then g enerally fell through the 20th. Particulate matter also rose beginning on the 9th and fell from the 15th through the 19th. At the end of the month, ozone levels stayed relatively high, while PM10 dropped off. The two pollutants seem to follow similar b ut not identical daily patterns.
The second Harford County Chart shows PM10 and ozone concentrations during the day on July 15, 1995. Both pollutants start at low levels in the morning and then rise beginning around 8 a.m. Both tend to fall off in the late evening hours.
In 1995 there were also a few jurisdictions in the Mid-Atlantic Region measuring very fine particles. PM2.5 monitors measure airborne levels of particles with a diameter of 2.5 microns or less. Like ozone, some PM2.5 particles are formed in the atmosphe re from chemical reactions involving other pollutants (sulfates, nitrates, and organics), while a greater portion of PM10 is directly discharged from sources.
The next two charts compare PM2.5 levels with other pollutants measured in Allegheny County, Pennsylvania. Like the Maryland data, these measurements were also taken in July 1995. Three sites in Allegheny County are shown. The PM2.5 site is located dow nwind of a major industrial facility. The Harrison Township site is about 22 miles to the north-northeast. There appears to be a similar pattern of rising and falling concentrations of ozone and PM2.5 at the two sites throughout the month.
The second Allegheny County chart shows concentrations throughout July 13. The ozone and nitrogen oxide measurements were made at Lawrenceville, about 11 miles north-northwest of the PM2.5 monitor. Allegheny County staff have also reviewed data for othe r days and found that PM2.5 is likely to be low during peak ozone hours, the opposite relationship shown in the daily Maryland chart and in the Maryland PM10 data.
The complexity shown in these charts may be due to the sources affecting the sites and to the chemical reactions involved in the air. The relationships between particulate matter and levels of ozone and other pollutants warrant further site-specific stud y.
|Sources:||Dick Wies, Maryland Department of the Environment, personal communication.|
|George W. Leney, Allegheny County Health Department, personal communication|
|Rich Scheffe, US Environmental Protection Agency, personal communication|
Chart: Hourly Ozone and PM10, Aldino Airport - Harford County, Maryland, July 1995
Chart: Maximum Daily Ozone and PM2.5 Ozone at Harrison Township and PM2.5 at Liberty Bono, July 1995 in Allegheny County
Chart: Hourly Ozone, NOx and PM2.5 Ozone and NOx at Lawrenceville and PM2.5 at Liberty Bono, July 13, 1995 in Allegheny County