Collocated Measurements of Light‐Absorbing Organic Carbon in PM_2.5: Observation Uncertainty and Organic Tracer‐Based Source Apportionment

Abstract

Organic matter (OM) constitutes a significant fraction (20%-90%) of fine particles with aerodynamic diameter less than 2.5 (PM 2.5 ) or 1.0 μm (

Time‐Resolved Measurements of PM2.5 Chemical Composition and Brown Carbon Absorption in Nanjing, East China: Diurnal Variations and Organic Tracer‐Based PMF Analysis

“…The misclassification of BrC sources based on low time‐resolved measurements is likely caused by the missing of diurnal source cycles. The coal combustion, microbial activity, and lubricating oil combustion factors were identified and well explained at the same study location and were not major sources of BrC (Gou et al., 2021; M. Xie et al., 2022b; Z. Xu et al., 2022). The stacked factor contributions of the PMF total and PMF summer solutions reasonably reflected the diurnal patterns of input species (Figure 5 and Figure S9 in Supporting Information ), but the peak values were usually underestimated.…”

“…To evaluate the light absorption per unit mass of WSOC, the solution mass absorption efficiency (MAE λ , w , m 2 g −1 C) was calculated as follows $$${\text{MAE}}_{\lambda ,w}=\frac{{\text{Abs}}_{\lambda ,w}}{{C}_{\text{WSOC}}}$$$ where C WSOC denotes ambient concentrations of WSOC (μg m −3 ). Since WIOC shows stronger light absorption than WSOC at the same location (M. Xie et al., 2022b), one fourth of each filter sample was extracted in 12 mL methanol. After filtration, the light absorbance ( A λ , m ), light absorption coefficient (Abs λ , m , Mm −1 ), and solution mass absorption efficiency (MAE λ , m , m 2 g −1 C) of the methanol extracts were determined in the same manner as those of the water extracts.…”

“…MEOC concentrations were calculated by multiplying OC concentrations by the average extraction efficiency of methanol (82.4%) from M. Xie et al. (2022b). In this study, Abs λ and MAE λ of water and methanol extracts at 365 nm were reported to compare with previous studies.…”

“…To alleviate the impacts of the gas‐particle partitioning process, non‐polar OMMs with p o, * L much greater than 10 −9 atm were also excluded (Table S2 in Supporting Information ). Light non‐polar OMMs in the ambient were mainly attributed to evaporation of crude oil and petroleum products, which accounted for an insignificant fraction (about 1%) of MEOC absorption (M. Xie et al., 2022b). The resulting whole data set (PMF whole ) contained 499 observations of 52 species, including six bulk species (NH 4 + , Ca 2+ , SO 4 2− , NO 3 − , OC, and WSOC), 44 OMMs (Table S2 in Supporting Information ), Abs 365, w , and Abs 365, m .…”

“…After filtration, the light absorbance (A λ,m ), light absorption coefficient (Abs λ,m , Mm −1 ), and solution mass absorption efficiency (MAE λ,m , m 2 g −1 C) of the methanol extracts were determined in the same manner as those of the water extracts. MEOC concentrations were calculated by multiplying OC concentrations by the average extraction efficiency of methanol (82.4%) from M. Xie et al (2022b). In this study, Abs λ and MAE λ of water and methanol extracts at 365 nm were reported to compare with previous studies.…”