Measurements, Gas/Particle Partitioning, and Sources of Nonpolar Organic Molecular Markers at a Suburban Site in the West Yangtze River Delta, China

Abstract

AbstractThis study seeks to understand the ambient levels, gas/particle partitioning, and sources of nonpolar organic molecular makers (OMMs) at a suburban site in Nanjing, China. Particle‐ and gas‐phase OMMs were collected using a medium volume sampler equipped with two quartz filters in series and a polyurethane foam (PUF)/XAD‐4/PUF (PXP) adsorbent sandwich. More than 100 pairs of filter and PXP samples were collected diurnally from September 2018 to September 2019. The concentration profiles of total n‐alkanes and polycyclic aromatic hydrocarbons were peaking at n‐C12–n‐C17 homologs (9.98 ± 5.43–38.4 ± 17.7 ng m−3) and naphthalene (92.5 ± 56.7 ng m−3), respectively, followed by decreasing concentrations with further increases in molecular weight. Three artifact correction methods with different pre‐assumptions on relative contributions of evaporation loss to backup filter measurements were used to separate particle‐ and gas‐phase OMMs. The resulting particle‐phase fractions showed significant differences for OMMs with vapor pressure <10−9 atm at 298.15 K. Absorptive gas/particle partitioning coefficients of OMMs were empirically calculated based on measurements and theoretically predicted for comparison. The results obtained under the three artifact correction methods suggested growing importance of evaporation loss with decreased vapor pressure. Positive matrix factorization (PMF) was performed for source apportionment using total (PMFtotal) and particle‐phase (PMFparticle) OMMs data, respectively. Besides eliminating the influence of gas/particle partitioning, the involvements of more volatile species and gaseous OMMs data improved the identification of specific emission sources, supporting the usage of total OMMs data over a wide vapor pressure range for PMF source apportionment.