Mixing state of biomass burning particles by single particle aerosol mass spectrometer in the urban area of PRD, China

Single particle aerosol mass spectrometer (SPAMS) was used to characterize the single particle size and chemical composition of submicron aerosols in the urban area of the Pearl River Delta region, China, for the period April 30 through May 22, 2010. A total of 696,465 particles were sized and chemically analyzed with both positive and negative ion spectra, in which 141,338 biomass burning particles were identified representing a significant source of submicron particles ∼20.3% by number. The results have revealed that biomass burning particles have experienced extensive atmospheric processing, finding that as much as 90.5% of the particles have internally mixed with secondary inorganic species. Biomass burning particles were clustered into six distinct particle groups, comprising of K–Ca-rich, K–Na-rich, K–organic carbon (K–OC), K–elemental carbon (K–EC), K–the mixture of OC and EC (K–OCEC) and K–Secondary. K–OC was the largest contributor with a fraction of 22.9%, followed by K–Secondary type (21.4%) and K–OCEC (19.0%). K–Na-rich type was observed in 11.9% of the particles and 90% internally mixed with EC. The fraction of nitrate in biomass burning particles was 10% higher than in the non-biomass burning particles. The sodium and potassium in biomass burning particles could exhibit high affinity for nitrate gases during neutralization reactions, facilitating the particulate nitrate formation. Meanwhile, the particulate sulfate in particles in the droplet-mode size was also enhanced. The results added appreciably to the knowledge of aerosol characteristics in the PRD region atmosphere and could be applied to the climate models.

► Biomass burning particles accounted for ∼20.3% by unscaled SPAMS number in PRD.
► 90.5% of the biomass burning particles internally mixed with sulfate and nitrate.
► K–OC was the largest contributor, followed by K–Secondary and K–OCEC mixture.
► Sulfate was preferentially mixed with the organics-containing particles.
► Biomass burning maybe facilitate the formation of particulate nitrate.