Heterogeneous reactions of particulate benzo[b]fluoranthene and benzo[k]fluoranthene with NO3 radicals

• Heterogeneous reactions of B[b]F and B[k]F with NO3 radicals are studied .
• Reaction products of the PAHs particles are observed.
• Effective rate constants for the reactions are obtained using a relative method.
• Effective NO3 uptake coefficients for the reactions are calculated.

Benzo[b]fluoranthene (B[b]F) and benzo[k]fluoranthene (B[k]F) are widespread priority pollutants of polycyclic aromatic hydrocarbons (PAHs), which can react with atmospheric oxidants during transport in the troposphere and lead to the formation of more toxic compounds. At present, the rates of heterogeneous reactions of B[b]F and B[k]F aerosols with NO3 radicals, an important atmospheric oxidant, are not fully understood. Thus, this study investigated the products and kinetics of heterogeneous reactions of suspended B[b]F and B[k]F particles with NO3 radicals in an aerosol reaction chamber at room temperature (293 ± 2 K) under atmospheric pressure. The reactions are monitored online using a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and an atmospheric gas analysis mass spectrometer. The mono-nitro-, di-nitro-, tri-nitro-products, and those products containing both nitro and ketone groups are observed with VUV-ATOFMS. The effective rate constants for heterogeneous reactions of particulate B[b]F and B[k]F with NO3 radicals under the experimental conditions are respectively estimated to (1.2 ± 0.1) × 10−12 cm3 molecule−1 s−1 and (5.8 ± 0.3) × 10−13 cm3 molecule−1 s−1 using a mixed-phase relative rate method, and the corresponding effective uptake coefficients are respectively estimated to 0.22 and 0.65. The lifetimes of particulate B[b]F and B[k]F at a typical concentration of NO3 radicals (5 × 108 molecule cm−3) in the lower troposphere during the night are estimated to 3.0 and 3.9 h, respectively. The experimental results of these heterogeneous reactions in the aerosol state provide supplementary knowledge for kinetic behaviors of airborne PAHs particles.