The role of secondary inorganic aerosol (SIA) species ammonium, nitrate and sulfateduring haze and fog episodes is investigated using hourly results for mass concentrations in PM2.5. At a suburban site in Hangzhou China 546 hourly samples were collected, analyzed and classified as �clear� (354), �haze� (144) or �fog� (48) depending on visibility and relative humidity. The contribution of SIA species to PM2.5 mass is 37% during clear episodes and increases to ~50% during haze and fog periods (Fig. 1). The mass contribution of nitrate to PM2.5 increases from 11% during clear to 20% during haze episodes and exceeds sulfate mass during haze, while near equal concentrations are observed during fog episodes. The role of relative humidity (RH) between concentrations of SIA species and visibility is examined and correlations show optima at 60-70% RH. These correlations show variation between SIA species and show better correlation of PM2.5 mass concentration solely with visibility (except NO3- at RH<50%). The acidity of the particles, expressed as total acidity [H+]Total, during clear, haze and fog periods are 6.39, -37.91 and -67.21 nmol m-3, respectively, indicating sulfate and nitrate are not neutralized by ammonium during clear periods, while there is sufficient ammonium to neutralize sulfate and nitrate during haze and fog periods. The nitrate to sulfate molar ratio as a function of the ammonium to sulfate molar ratio indicates nitrate formation during fog starts at higher ammonium to sulfate ratio molar ratio compared to clear and haze periods (Fig. 2). The relationship between excess ammonium and nitrate shows about 30% excess ammonium is bound to species other than nitrate. During haze and fog, the nitrate oxidation ratio increases by a factor 1.6-1.7 and the sulfur oxidation ratio increases by a factor 1.2-1.5, indicating SIA precursor gases NO2 and SO2 are involved in the reduced visibility.  

Using hourly measurements to illustrate the distinct role of secondary inorganic aerosol in PM<sub>2.5</sub> during haze and fog

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.

Using hourly measurements to illustrate the distinct role of secondary inorganic aerosol in PM2.5 during haze and fog

Using hourly measurements to illustrate the distinct role of secondary inorganic aerosol in PM_2.5 during haze and fog