Agricultural amonia emmissions and particulate matter

In the atmosphere, ammonia reacts with nitric and sulphuric acid and produces low volatile salts. These can significantly contribute to particulate mass by either partitioning onto existing particles or building new particles. The acids are mainly produced from precursors arising from traffic, industry and households. In contrast, ammonia originates by about 90 % from agricultural sources. As ammonia is a very light molecule, it only contributes around 10 % of the particulate mass, but it is involved in the production of about 40 % of the particle mass. Therefore, ammonia emission controls appear to be an effective way to reduce particulate matter. However, there is no 1:1 relation between the reduction of ammonia emissions and the reduction of ambient particulate matter. The effectiveness is significantly reduced by two factors: firstly secondary inorganic aerosols only account for 40 % of total particulate mass and secondly the boundary layer air in Switzerland is over-saturated with ammonia. Our analyses demonstrate that a 10 % reduction of ammonia emissions only results in a 0.5 % decrease of particulate matter. Larger reductions are more effective, a 50 % reduction of ammonia emissions yields about a 3 to 10 % decrease in particulate matter.