Ozone-nitrogen dioxide-NPAH heterogeneous soot particle reactions and modeling NPAH in the atmosphere

The degradation of particle-associated nitro polycyclic aromatic hydrocarbons (NPAH) with ozone (O-3) and O-3 + nitrogen dioxide (NO2) was investigated. Deuterated and native NPAH coated on diesel soot or wood smoke reacted with 0.6-0.9 ppm O-3 and 0.03-0.5 ppm nitrogen oxides (NOx) in a 190-m(3) outdoor smog chamber. A sampling train consisting of an annular denuder, filter, and another annular denuder was used for the collection of gas acid particle phase PAH and NPAH. Degradation of deuterated and native NPAH was observed in the presence of O-3 and O-3 + NO2 in both cool and warm temperatures (2 to 20 degrees C). The degradation of particle NPAH from chamber experiments was modeled with a proposed NPAH reaction mechanism combined with photochemical smog mechanism. The degradation rate constants of 1- and 2-nitropyrene and 2-, 3-, and 8-nitrofluoranthene with O-3 ranged from 0.0015 to 0.0025 ppm(-1) min(-1) The rate constant of particle NPAH with NO2-NO3-N2O5 was less than 0.001 ppm(-1) min(-1). The results have shown that particle oxidation of NPAH by 03 is not as important as photodegradation of NPAH in daytime, but it may be the main loss process for NPAH at night. The decay of particle PAH was also modeled, and the results were compared with NPAH data. The results from this study and a NPAH photodegradation study were added to a previous PAH and NPAH mechanism, and outdoor chamber experimental data were simulated with a photochemical kinetic simulation package.