Formation of sulfate-nitrate-ammonium (SNA) aerosols can be limited by ammonia emissions. Consider that we are in such a chemical regime and that we decrease ammonia emissions in order to decrease PM2.5 pollution. Eventually, as ammonia emissions get low enough, we will exit that regime.
When that happens, should we switch to decreasing SOâ‚‚ emissions or to decreasing NOx emissions in order to further decrease PM2.5 ?
