Photochemistry and partitioning of semivolatile nitro-PAH in the atmosphere.

A 190 m(3) outdoor smog chamber was used to study partitioning and photochemistry of 1- and 2-nitronaphthalene. The partitioning experiments were conducted at night. The photochemical formation of nitronaphthalenes was studied using a mixture of naphthalene, propylene, NOx and diesel particles. The buildup in the gas phase was followed by a rapid photolysis of 1-nitronaphthalene, whereas 2-nitronaphthalene decayed more slowly. In a separate daytime experiment, photolysis rate constants were determined relative to k(NO2) to be 0.07xk(NO2) and 0.005xk(NO2) for 1- and 2-nitronaphthalene, respectively. Our results confirm that gas-phase photolysis is the major degradation pathway for 1-nitronaphthalene, whereas for 2-nitronaphthalene other pathways may also be important. Evidence is provided that partitioning equilibrium is maintained even when the gas-phase components are decaying rapidly. A nitronaphthalene mechanism has been successfully implemented in the photochemical smog mechanism, Carbon Bond-4.