Vehicular Ammonia Emissions Significantly Contribute to Urban PM2.5 Pollution in Two Chinese Megacities

Ammonia (NH3) plays a vital role in the formation of fine particulate matter (PM2.5). Prior studies have primarily focused on the control of agricultural NH3 emissions, the dominant source of anthropogenic NH3 emissions. The air quality impact from vehicular NH3 emissions, which could be particularly important in urban areas, has not been adequately evaluated. We developed high-resolution vehicular NH3 emission inventories for Beijing and Shanghai based on detailed link-level traffic profiles and conducted atmospheric simulations of ambient PM2.5 concentrations contributed by vehicular NH3 emissions. We found that vehicular NH3 emissions shared high proportions among total anthropogenic NH3 emissions in the urban areas of Beijing (86%) and Shanghai (45%), where vehicular NH3 was primarily emitted by gasoline vehicles. Local vehicular NH3 emissions could be responsible for approximately 3% of urban PM2.5 concentrations during wintertime, and the contributions could be much higher during polluted periods (similar to 3 mu g m-3). We also showed that controlling vehicular NH3 emissions will be effective and feasible to alleviate urban PM2.5 pollution for megacities in the near future.

Automated summary

Previous studies have mainly focused on agricultural ammonia emissions and neglected the impact of vehicular ammonia emissions on air quality in cities. This study developed high-resolution emission inventories for Beijing and Shanghai based on traffic data and simulated the contribution of vehicular ammonia emissions to PM2.5 concentrations. It was found that vehicular ammonia emissions accounted for a significant proportion of total anthropogenic ammonia emissions in urban areas, and could contribute to approximately 3% of urban PM2.5 concentrations during winter. Controlling vehicular ammonia emissions is an effective measure to mitigate urban PM2.5 pollution in the future.