Heterogeneous reaction kinetics influencing benzo(a)pyrene global atmospheric distribution and related lifetime lung cancer risk

Abstract. Benzo(a)pyrene (BaP) is a ubiquitous and hazardous air pollutant that increases the risk of lung cancer. Heterogeneous oxidation by ozone limits the atmospheric concentrations and long-range transport potential of BaP, but the actual oxidation rates and chemical lifetimes of BaP under varying atmospheric conditions are not yet well constrained. In this study, we employ the ECHAM/MESSy atmospheric chemistry model for the simulation of semivolatile organic compounds (using the SVOC submodel) with coupled surface compartments to compare four different kinetic schemes of BaP oxidation and assess the pollutant’s global distribution and associated lung cancer risks. We find that a kinetic scheme considering the temperature and humidity dependence of particle phase state, mass transport, and reaction rate coefficient is best suited to reproduce ambient observations, yielding mean global atmospheric lifetime and total environmental residence times of ~5 hours and ~20 days, respectively. Estimates of the BaP-related lung cancer risk surpass 10^-5 (i.e., 10 excess cases per million people) in central and eastern Europe, parts of the Russian Far East, northern India, Pakistan, and western China, and surpass 10^-4 in central, eastern, and northeastern China.