Organic matter accounts for a large fraction of fine particulate matter (i.e., PM_2.5). The organic composition of PM_2.5 at a molecular level has yet to be achieved, hindering a full understanding of the climatic impacts and health effects of PM_2.5. Compounds containing aromatic rings are closely associated with optically active brown carbon and toxicologically important quinones.

In this work, a group of nine aromatic organic acids including three phthalic acids, four phenolic acids and two benzene-tricarboxylic acids (BTCAs) in PM_2.5 are studied for their abundance and potential sources through quantifying their ambient concentrations at four sites in the Pearl River Delta Region, China.

Concentrations of individual aromatic acids in a total of 231 PM_2.5 samples collected throughout...[ Read more ]

Organic matter accounts for a large fraction of fine particulate matter (i.e., PM_2.5). The organic composition of PM_2.5 at a molecular level has yet to be achieved, hindering a full understanding of the climatic impacts and health effects of PM_2.5. Compounds containing aromatic rings are closely associated with optically active brown carbon and toxicologically important quinones.

In this work, a group of nine aromatic organic acids including three phthalic acids, four phenolic acids and two benzene-tricarboxylic acids (BTCAs) in PM_2.5 are studied for their abundance and potential sources through quantifying their ambient concentrations at four sites in the Pearl River Delta Region, China.

Concentrations of individual aromatic acids in a total of 231 PM_2.5 samples collected throughout 2012 are within the range from below detection limit to a few hundred ng m-³. Inter-species correlation analysis with known PM source tracers, such as levoglucosan (a specific biomass burning tracer) and sulfate (a major component of secondary origin), reveals different source origins for the nine aromatic acids. The four phenolic acids (i.e., 3-hydroxy benzoic acid, 4-hydroxy benzoic acid, syringic acid and vanillic acid), all possessing partial lignin structures, are highly-correlated among themselves and with levoglucosan, indicating their likely association with biomass burning emissions. The two BTCA acids, 1,2,4-BTCA and 1,3,5-BTCA, have moderate correlation with sulfate (R²: 0.42-0.56) but no correlations with levoglucosan (R²: 0.04-0.08), suggesting a dominant secondary formation origin. The three phthalic acids (o-, m-, p-phthalic acids) have moderate correlations with sulfate, levoglucosan, and a number of polycyclic aromatic hydrocarbons (PAHs) and they are slightly more correlated with sulfate than levoglucosan, indicating multiple significant sources. This study provides an important data set for establishing quantitative links between molecular composition of OM and the optical and toxicological properties of PM_2.5 as well as shedding lights to seek effective tracers for PM_2.5 sources.