LAUSR

The primary sources for inorganic aerosols from biomass burning are rather negligible; but they are predominantly formed chemically following emission of their precursors (e.g., SO2, NH3, HOx, and NOx). The biomass burning contributions to some of the precursors can be considerable. Accordingly, we quantify the impact of the emissions on major inorganic aerosols in April-October 2012-2014 using a regional model simulation verified by extensive surface observations throughout the US. Simulated CO enhancements on an hourly basis are used to classify the US into weak-moderate (5 20 ppbv). This separation not only facilitates the identification of the spatial frequency of the impact but also helps to filter out non-impacted periods, enabling us to focus on long-term contributions. Despite the nonlinear responses of several trace gases to emissions, we observe increases (weak-moderate, strong) in daily surface SO42- (1.16±0.32, 6.57±4.65 nmol/m3), NO3- (0.36±0.63, 4.70±7.05 nmol/m3) and NH4+ (2.70±0.92, 17.82±15.17 nmol/m3) on a national scale. These primarily resulted from i) increases in daily surface SO2 (0.02±0.01, 0.10±0.07 ppbv), afternoon OH (1.28±4.24, 12.82±23.76 ppqv), and H2O2 (0.06±0.02, 0.10±0.08 ppbv), which may have accelerated the conversion of S(IV) to S(VI), and ii) increases in daily surface NH3 (1.08±0.73, 8.61±7.73 nmol/m3) and HNO3 (1.44±0.48, 7.15±4.25 nmol/m3), which could have produced more particle-phase NH4NO3. In the West, where atmospheric moisture is limited, enhanced SO42- leaves less available water for NH4NO3 to become ions. Our results suggest that the major inorganic aerosols enhancement (mass) can reach to 23% of that of the carbonaceous aerosols.