The photochemistry of anthropogenically emitted nonmethane hydrocarbons (NMHC's) in the troposphere was studied by (1) developing a chemical mechanism which includes the reactions of anthropogenically emitted NMHC's and their associated intermediates (alkoxy and alkylperoxy radicals, aldehydes, peroxyacetylnitrate (PAN) with both hydrocarbon and inorganic species and (2) performing model calculations with the mechanism using a one-dimensional photochemical model of the troposphere. Calculations represent the region between 30 N and 60 N latitude. The inclusion of the chemistry of NMHC species with short lifetimes against chemical destruction provided detailed information about both the profiles of short-lived NMHC species and the overall NMHC chemistry. Surface concentrations of emitted hydrocarbons, NOx, and HNO3 were well simulated. Only slight changes in the profiles of OH, HO2, NOx and HNO3 were obtained when the NMHC chemistry was included. The inorganic nitrogen budget is not significantly altered by the inclusion of NMHC chemistry. The sensitivity of the PAN profile to changes in the magnitudes of NMHC emissions and to the introduction of a heterogeneous loss term to simulate advection was also assessed. Advection may be an important removal process for PAN in the mid-latitudes.