PMF-GAS methods to estimate contributions of sources and oxygen for PM 2.5 , based on highly time-resolved PM 2.5 species and gas data

Abstract

To gain detailed insight into the gaseous sources of PM 2.5 , three kinds of positive matrix factorization were developed and applied to hourly elemental and gaseous data (PMF-GAS). According to the results of PMF-GAS1, which relied on gaseous markers to enhance source discrimination, crustal dust, vehicular exhaust, coal combustion, sulfate and nitrate (CD 1 , VE 1 , CC 1 , SUL 1 and NIT 1 ) directly contributed 20%, 17%, 15%, 34% and 14% to the PM 2.5 , respectively. Using PMF-GAS2, which summed species found in PM 2.5 , and their corresponding precursors to estimate the overall influence of primary sources, the total contribution from CD 2 , VE 2 and CC 2 to PM 2.5 was quantified as 30%, 29% and 41%, respectively. Finally, PMF-GAS3 quantified the contribution of oxidation (OXI 3 ; 27%) based on the relationships between the species and their precursors. NH 4+ was found mostly in CD 2 and CD 3 but also in SUL 1 and NIT 1 , implying that crustal dust can provide alkaline conditions for the formation of ammonium salts. High correlations were found between corresponding source contributions, but CD 1 showed relatively weak links with CD 2 and CD 3 due to NH 4+ being present in different factors. A fully populated map of classical bootstrap (BS) runs implies the high stability of these PMF-GAS results.