Observational Carbonyl Compounds in Gaseous and Particulate Phase over Urban Beijing

Carbonyl compounds are ubiquitous in the atmosphere. They play an important role in the atmospheric chemistry, serving as reservoirs of radicals (OH, HO₂ and RO₂) and precursors of ozone and secondary organic aerosols (SOA). In addition, carbonyl compounds have a detrimental effect on human health. Therefore, it is of great scientific significance and value to measure the levels of carbonyl compounds in the atmosphere and study their sources, which can provide a basis for the government to formulate effective control measures. The present study carried out four field observations in urban Beijing in summer and winter. Gaseous and particulate samples were collected simultaneously. In the gas phase, we detected ten carbonyl compounds. Formaldehyde, acetaldehyde and acetone were the most abundant species. The concentrations of carbonyl compounds showed seasonal variations. The levels in summer were generally higher than those in winter. In the particle phase, we detected six carbonyl compounds. Glyoxal, formaldehyde and acetaldehyde were the most abundant species. Based on the measured gaseous and particulate concentrations, we estimated the gas-particle partitioning coefficients (K_p) of carbonyl compounds. It was found that the field-measured K_p values were 4-6 orders of magnitude higher than the values predicted by Pamkow's absorptive model, which indicated the importance of the heterogeneous reactions. In addition, the gas-particle partitioning coefficients of carbonyls were one order of magnitude higher than those in summer owing to the effect of temperature. Relative humidity (RH) is also an important influencing factor. Taking formaldehyde and glyoxal as examples, under low RH (20-70%), their K_p values experienced a rapid decline and then increased slightly with increasing RH. High relative humidity had little impact on the gas-particle partitioning of carbonyls. We employed the PMF model to apportion the sources of carbonyl compounds. In summer, the sources of carbonyls included secondary formation, biogenic emissions, gasoline evaporation, vehicular exhaust and solvent utilization. In winter, the biogenic factor was not recognized but coal burning was recognized. Secondary formation contributed most to the total measured carbonyl compounds in summer, while in winter, vehicular exhaust was the largest contributor. Except secondary formation and biogenic emissions, other factors can be classified as primary anthropogenic sources.