A study on three factors influencing uptake rates of nitric acid onto dust particles

Abstract

Recent studies have indicated that the observed nitric acid (HNO3) uptake rates (RHNO3) onto dust particles are much slower than RHNO3 used in the previous modeling studies. Three factors that possibly affect RHNO3 onto dust particles are discussed in this study: (1) the magnitude of reaction probability of HNO3 (γHNO3), (2) aerosol surface areas, and (3) gas-phase HNO3 mixing ratio. Through the discussion presented here, it is shown that the use of accurate γHNO3 is of primary importance. We suggest that the use of γHNO3 values between ~10-3 and ~10-5 produces more realistic results than the use of γHNO3 values between ~10-1 and ~10-2 does, more accurately modeling the nitrate formation characteristics on/in dust particles. We also discuss two different types of aerosol surface area, active and geometric, since the use of different aerosol surface areas often leads to an erroneous result in RHNO3. In addition, the levels of the gas-phase HNO3 are investigated with the example cases of TRACE-P DC-8 flights in East Asia. The HNO3 levels were found to be relatively high, indicating that they can not limit nitrate formation in dust particles.