Effects of seed particles Al 2 O 3 , Al 2 (SO 4 ) 3 and H 2 SO 4 on secondary organic aerosol

Seed particles Al2O3, Al2(SO4)3 and H2SO4 were selected to investigate their effects on secondary aerosol (SA) formation in toluene/NO x photooxidation under sulfur dioxide (SO2) and ammonia (NH3). Effect of seed particles on SA formation was related to their acid-base properties and the presence of acid or alkaline gases. Under NH3-poor condition, SA formation increased with increasing SO2 concentration due to the acid-catalyzing effect of the oxidation products of SO2 (i.e. H2SO4). The enhancing effect of SO2 became unobvious under NH3-rich condition, because NH3 would eliminate the acid-catalyzing effect by neutralizing the acid products. Acidic seeds H2SO4 accelerated SA formation under either SO2 or NH3 condition. Weak acidic Al2(SO4)3 seeds didn’t affect obviously on SA formation. The inhibiting effect of amphoteric seeds Al2O3 on SA formation was related to the presence of SO2 / NH3 due to their acid-base property. Under NH3-poor condition, the inhibiting effect of Al2O3 on SA formation decreased with increasing concentration of SO2, while under NH3-rich condition, the inhibiting effect wasn’t remarkable.