Heterogeneous N<sub>2</sub>O<sub>5</sub> reactions on atmospheric aerosols at four Chinese sites: Improving model representation of uptake parameters

Abstract

Heterogeneous reactivity of N 2 O 5 on aerosols is a critical parameter in assessing NO x fate, nitrate production, and particulate chloride activation. Accurate measurement of its uptake coefficient (γ N2O5 ) and representation in air quality model are challenging, especially in the polluted environment. With an in-situ aerosol flow tube system, the γ N2O5 was directly 20 measured on ambient aerosols at two rural sites in northern and southern China. The results were analyzed together with the γ N2O5 derived from previous field studies in China to obtain a holistic picture of N 2 O 5 uptake and the influencing factors under various climatic and chemical conditions. The field derived/measured γ N2O5 was generally promoted by the aerosol water content and suppressed by particle nitrate. Significant discrepancies were found between the measured γ N2O5 and that estimated from laboratory-determined parameterizations. An observation-based empirical parameterization was derived in the present 25 work, which better reproduced the mean value and variability of the observed γ N2O5 . Incorporating this new parameterization in a regional air quality model (WRF-CMAQ) has improved the simulation of nitrogen oxides and secondary nitrate in the polluted regions of China.

Persistent Heavy Winter Nitrate Pollution Driven by Increased Photochemical Oxidants in Northern China

“…We incorporated up-to-date reactive nitrogen chemistry into the CMAQ model, including an improved N 2 O 5 heterogeneous uptake parametrization and comprehensive HONO sources . As shown in Figure c–f, the revised CMAQ model well captured the observed spatial and temporal variability of NO 3 – and the increasing trend of its proportion in PM 2.5 with increasing pollution levels.…”

“…The contributions of NO 3 − to PM 2.5 increased from 12% for PM 2.5 < 35 μg/m 3 to 23.3% for PM 2.5 > 150 μg/m 3 (Figure 1f), indicating enhanced NO 3 − formation and the increasing role of NO 3 − in heavy haze pollution. We incorporated up-to-date reactive nitrogen chemistry into the CMAQ model, including an improved N 2 O 5 heterogeneous uptake parametrization 44 and comprehensive HONO sources. 45 As shown in Figure 1c−f, the revised CMAQ model well captured the observed spatial and temporal variability of NO 3…”