Isotopic constraints on heterogeneous production of nitrate in extreme haze in Asia
Abstract
Frequent outbreaks of prolonged haze events have become a prevalent challenge to public health and environmental management in many developing countries in Asia. China, in particular, has suffered from wintertime PM2.5 pollution over the last two decades. Some recent observational studies have suggested that nitrate production is becoming more important in haze events after strong regulations on SO2 emissions were introduced in China. Nevertheless, the formation mechanisms of nitrate and their relative importance in polluted air are still poorly understood. This is exemplified by persistent overestimate of nitrate concentration in many air quality models. In this study, we implement several updates to the heterogeneous chemistry scheme in the GEOS-Chem global chemical transport model (GC) and examine the roles of various heterogeneous mechanisms in producing inorganic nitrate in urban air. The model simulations are evaluated with the wintertime measurements of NOy and stable oxygen isotopes in nitrate (Δ17O(NO3-)) in northern China. Our preliminary results suggest that the current version of GC overestimates the contribution from NO2 hydrolysis, which is the dominant nitrate formation pathway on polluted days in model, and underestimates N2O5 hydrolysis. After suppressing the uptake rate of NO2 hydrolysis in the model to better match the isotope observations, modeled HONO concentration reduces dramatically. Alternative HONO sources, such as nitrate photolysis or ground surface reactions, have to be introduced into the model to explain the HONO observations in polluted air. Overall, the updated representation of heterogeneous mechanisms in GC leads to better agreement with measurements of oxygen isotopes and reduces the model's high bias in simulating nitrate concentration in urban air. We also investigate how these model updates may impact air quality in other Asian cities.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A51C..03C
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0317 Chemical kinetic and photochemical properties;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0345 Pollution: urban and regional;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES