Persistent sensitivity of Asian aerosol to emissions of nitrogen oxides

We use a chemical transport model and its adjoint to examine the sensitivity of secondary inorganic aerosol formation to emissions of precursor trace gases from Asia. Sensitivity simulations indicate that secondary inorganic aerosol mass concentrations are most sensitive to ammonia (NH₃) emissions in winter and to sulfur dioxide (SO₂) emissions during the rest of the year. However, in the annual mean, the perturbations on Asian population-weighted ground-level secondary inorganic aerosol concentrations of 34% due to changing nitrogen oxide (NO_x) emissions are comparable to those from changing either SO₂ (41%) or NH₃ (25%) emissions. The persistent sensitivity to NO_x arises from the regional abundance of NH₃ over Asia that promotes ammonium nitrate formation. IASI satellite observations corroborate the NH₃ abundance. Projected emissions for 2020 indicate continued sensitivity to NO_x emissions. We encourage more attention to NO_x controls in addition to SO ₂ and NH₃ controls to reduce ground-level East Asian aerosol. Key Point Ground-level Asian aerosols are sensitive to nitrogen oxide emissions.