Effect of vertical parameterization of a missing daytime source of HONO on concentrations of HONO, O3 and secondary organic aerosols in eastern China

Abstract

Unexpectedly high daytime concentrations of nitrous acid (HONO) measured by field observations cannot be explained by theoretical calculations, implying that there may be a missing source of HONO in the daytime (Pmissing). The value of Pmissing near the ground (PGmissing) is different from that measured higher in the atmosphere (PHmissing) according to previous field studies, but the contribution of the vertical Pmissing profile in the atmospheric boundary layer (ABL) to air quality remains unknown. We derived a new formula PGmissing = 0.180 × J(NO2) [ppb s−1] based on field measurements near the ground, where J(NO2) is the photolysis frequency of NO2, and used the value of PHmissing inferred from Zeppelin measurements in the troposphere to parameterize Pmissing in the ABL. This parameterization was incorporated into the Weather Research and Forecasting model with Chemistry (WRF-Chem) to quantify the vertical effects of Pmissing on the concentrations of HONO, O3 and secondary organic aerosols (SOAs) in eastern China. Our results showed that PGmissing and PHmissing together further narrowed the gap between the simulations and observations, leading to a daytime increase in HONO concentrations of about 160 ppt near the ground in summer, autumn and winter compared with PGmissing only, an increase in the daytime concentrations of O3 of 8–37 ppb within the ABL in almost all of the studied domain in summer (1–19 ppb in winter and 4–21 ppb in autumn) and the largest hourly increase in the concentration of SOAs of 22.5 (18.6) μg m−3 in winter (summer). The results indicated that HONO sources near the ground have a limited effect on the HONO concentrations in the upper ABL even in summer in the presence of strong convective activities. The HONO increase in the upper ABL can affect the concentration of HONO near the ground. When PGmissing was inserted into each model layer in the ABL, the concentrations of HONO higher in the atmosphere were substantially overestimated, suggesting that observations of the vertical distribution of HONO in the ABL are required in polluted areas.