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

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