The interaction of particulate matter and gaseous automobile exhaust in the city of Graz, Austria.

Aerosol particles collected at urban locations contain a significant portion of automobile exhaust emissions, especially lead and zinc. The most important emitted gases, carbon monoxide (CO), hydrocarbons (HC), and the nitrogen oxides (NOx) play an important role in the formation of photochemical smog in urban areas. Nitrate formation through heterogeneous reactions on dust particles may provide a removal mechanism for the nitrogen oxides in the atmosphere. As a consequence dust can reduce ozone formation rates by up to 25%. At 47 sites within the city of Graz, Austria dust particles were collected. Two hundred particles with a diameter of about 1 microns were analyzed with a Laser Microprobe Mass Analyzer (LAMMA) for each sampling point: one half for laser generated cations and the other half for anions. The frequencies of occurrence of elements in 100 particles were used as a measure for the air quality. Isolines (lines of equal element frequencies) were employed to outline polluted regions and identify the sources of dust particles. A summation method was used to monitor nitrogen oxides. Particulate nitrate correlates well with lead frequencies in aerosols as well as with NOx levels. This indicates that the NOx emitted by traffic exhaust is at least partially deposited on particulate matter.