Comment on acp-2021-549

Abstract

An ensemble-variational inversion system is developed for the estimation of ammonia emissions using ammonia retrievals from the Cross-track Infrared Sounder (CrIS) for use in the Global Environmental Multiscale – Modelling Air quality and Chemistry (GEM-MACH) chemical weather model. A novel hybrid method to compare logarithmic retrieval parameters to model profiles is presented. Inversions for the monthly mean ammonia emissions over North America were performed for May to August 2016. Inversions using the hybrid comparison method increased ammonia emissions at most locations within the model domain, with total monthly mean emissions increasing by 11–41 %. The use of these revised emissions in GEM-MACH reduced biases with surface ammonia observations by as much as 25 %. The revised ammonia emissions also improved the forecasts of total (fine+coarse) ammonium and nitrate and ammonium wet deposition, with biases decreasing by as much as 13 %, but did not improve the forecasts of just the fine components of ammonium and nitrate. An additional area of 1.3 × 105 km2 of upland forests in Canada were estimated to exceed the ecosystem's critical load due to the changes in ammonia deposition from the inversion. A comparison of biases resulting from inversions using different comparison methods shows favourable results for the hybrid comparison method.