Estimation of actinic flux and photolysis rate constant of NO2 from aerosol size data

Aerosol mass measurements made using Andersen cascade impactor at different locations in an urban area were used to study the variation in power-law e xponent in the Junge-type number distribution. The discrete mass size data were inverted by modified Twomey algorithm to obtain continuous mass size d istribution from which number distributions were derived. These were used f or evaluating actinic fluxes and hence NO2 photolysis rate constants employ ing a radiative transfer model with delta-Eddington approximation. Results of the spatial variation of Junge power-law exponent over the urban region are presented. The relative magnitude of photolysis rate constants over regions with differing aerosol emission characteristics are illustrate d Parametric studies indicated the importance of considering fractional ele mental carbon content of the aerosols in the atmosphere. Results of a limit ed validation study of the model are also presented using quartz crystal mi crobalance impactor data at one of the sites. (C) 1999 Elsevier Science Ltd . All rights reserved.