Investigation on heterogeneous reactions of reactive oxidized nitrogen species with urban particles using iodide-chemical ionization mass spectrometry

Abstract

We investigated the heterogeneous reactions of HNO₃ and NO₂ on the surface of ambient urban particulate matter, which were conducted in a Teflon bag under dark conditions. Iodide-chemical ionization mass spectrometry, a real-time mass spectrometry approach, was used to measure HNO₃ and HONO, while NO and NO₂ were measured by a NO/NO_x monitor and a cavity attenuated phase shift spectroscopy-NO₂ monitor, respectively, in real-time. In experiments examining the heterogeneous reaction of HNO₃ on the surface of the urban particles, no formation of NO and NO₂ was observed under dark conditions (initial surface concentration of urban aerosols, 8.6 × 10⁷ nm² cm⁻³), but the formation of NO, NO₂, and HONO was observed after irradiation by black lights. Since a similar phenomenon was also observed without introduction of the particulate matter, the heterogenous reaction with light was concluded to have occurred on the inner surface of the Teflon bag. In experiments examining the heterogeneous reaction of NO₂ on the surface of urban particles, HONO was likely formed on the surfaces of the urban particles, but the yield of HONO suggested that the reaction on the urban particles was less efficient than that on the surface of soot particles.

Graphical Abstract