Theoretical model for the evaporation loss of PM_2.5 during filter sampling

The evaporation losses of PM_2.5 particles in eight different size ranges corresponding to the 4th-10th stages and after filter of the MOUDI were calculated theoretically and then integrated to obtain the total PM_2.5 evaporation loss. Results show that when PM_2.5 particles are nearly neutral with pH in the range of 7-8, the evaporated concentrations predicted by the present model agree well with the experimental data with an average absolute difference of 20.2±11.1%. When PM_2.5 aerosols are acidic with pH less than 3.5, additional loss of nitrate and chloride can occur due to chemical interactions between collected particles and strong acids which are not considered in the present model. Under pH neutral conditions, the theoretical model was then used to examine the effect of PM_2.5 concentration, gas-to-particle ratio, ambient temperature and relative humidity on the extent of evaporation loss. Results show that evaporated PM_2.5 concentration increases with increasing temperature and decreasing relative humidity, PM_2.5 concentration and gas-to-particle ratio.