Are Cars or Trees More Important to Particulate Matter Air Polution?
Air pollution in the form of particulate matter (PM) originates from both human activities and “natural” phenomena. Setting and achieving National Ambient Air Quality Standards (NAAQS) for PM has to take into account the latter since they are in general less controllable than the former. One of the elusive contributors to “natural” PM, particularly during summertime, is biogenic secondary organic aerosol (SOA), which results in the formation of PM from atmospheric gas-to-particle conversion of volatile organic compounds (VOC) emitted by vegetation. Theoretical estimates of the importance of biogenic SOA as a component of summertime PM differ greatly, ranging from negligible to dominant, because of uncertainties in both the conversion mechanism, and the amount and characteristics of biogenic VOC emissions. However, quite direct experimental estimates can be obtained by measuring the amount of the naturally-occurring radioactive isotope 14C (radiocarbon) in a PM sample. The method depend
