Interactions between diesel emissions and gaseous copollutants in photochemical air pollution: Some health implications

Abstract A complete assessment of the health effects of diesel emissions must take into account the possible chemical transformations (and associated biological impacts) of particulate organic matter (POM) due to reactions with the many gaseous copollutants which have now been unambiguously demonstrated to be present in atmospheres burdened by photochemical air pollution. These copollutants include the “trace” species, nitric (HNO 3 ) and nitrous (HONO) acids, the nitrate radical (NO 3 ), formaldehyde (H 2 CO) and formic acid (HCOOH), as well as the criteria pollutants, ozone (O 3 ) and nitrogen dioxide (NO 2 ). Techniques for establishing the atmospheric concentrations of the trace pollutants (and their spatial and temporal variations) are briefly described, and we present results of investigations into the reactions of polycyclic aromatic hydrocarbons (PAH) coated on filters and exposed to ambient concentrations of O 3 and NO 2 . Environmental health implications of these results are discussed and include the potential for sampling “artifacts” and their possible effects on the correlation (or lack thereof) between ambient PAH levels and urban lung cancer rates, as well as the problems associated with understanding the appropriate POM “dose” to be employed in animal testing and assessments of impacts on human health.