Fossil and contemporary fine particulate carbon fractions at 12 rural and urban sites in the United States

Abstract

[1] Fine particulate matter collected at two urban, four near-urban, and six remote sites throughout the United States were analyzed for total carbon (TC) and radiocarbon ( 14 C). Samples were collected at most sites for both a summer and winter season. The radiocarbon was used to partition the TC into fossil and contemporary fractions. On average, contemporary carbon composed about half of the carbon at the urban, $70-97% at near-urban, and 82-100% at remote sites. At Phoenix, Arizona, and Seattle, Washington, one monitor was located within the urban center and one outside to assess the urban excess over background concentrations. During the summer the urban and rural sites had similar contemporary carbon concentrations. However, during the winter the urban sites had more than twice the contemporary carbon measured at the neighboring sites, indicating anthropogenic contributions to the contemporary carbon. The urban fossil carbon was 4-20 times larger than the neighboring rural sites for both seasons. Organic (OC) and elemental carbon (EC) from TOR analysis were available. These and the radiocarbon data were used to estimate characteristic fossil and contemporary EC/TC ratios for the winter and summer seasons. These ratios were applied to carbon data from the Interagency Monitoring of Protected Visual Environments network to estimate the fraction of contemporary carbon at mostly rural sites throughout the United States. In addition, the ratios were used to develop a semiquantitative, lower bound estimate of secondary organic carbon (SOC) contribution to fossil and contemporary carbon. SOC accounted for more than one-third of the fossil and contemporary carbon.

Reactive intermediates revealed in secondary organic aerosol formation from isoprene

“…In the presence of anthropogenic pollutants, such as NO 2 and acidic aerosol produced from the oxidation of SO 2 , SOA mass yields from isoprene under highand low-NO x conditions, respectively, increase substantially. Because isoprene is estimated to be the largest single contributor to global SOA, these results may help to resolve two existing dilemmas in atmospheric chemistry: (i) Radiocarbon ( 14 C) data consistently indicate that well over half of the ambient SOA is of modern (biogenic) origin (7,33), whereas correlations between water-soluble organic carbon and anthropogenic tracers, such as CO, suggest that much of the SOA is actually of anthropogenic origin (34,35); and (ii) comparisons between measured and predicted SOA based on known precursors suggest that there is a substantial amount of "missing urban SOA" not included in current models (35)(36)(37). Revising the chemistry of isoprene in regional and global SOA models could lead to a decrease in this discrepancy; however, the measurement and parameterization of aerosol acidity requires additional work.…”

Characteristics of Organic and Elemental Carbon in PM2.5 and PM0.25 in Indoor and Outdoor Environments of a Middle School: Secondary Formation of Organic Carbon and Sources Identification

“…Joint approaches: They include approaches such as the EC-tracer method combined with radiocarbon ( 14 C) analysis [29], radiocarbon analysis with chemical mass balance (CMB) [30], and the direct estimation of SOC with input of secondary species when applying the positive matrix factorization (PMF) model [31]. Last, aerosol mass spectrometry (AMS) is an advanced approach providing high time resolution [32].…”

Water-soluble organic carbon (WSOC) and its temperature-resolved carbon fractions in atmospheric aerosols in Beijing

“…Sources of WSOC have been shown to be complex. They are emitted directly from combustion, industrial, and natural sources (primary) and/or formed through secondary processes such as homogeneous gas-phase and/or heterogeneous aerosol-phase oxidation (secondary) (Claeys et al, 2004;Koch et al, 2007;Schichtel et al, 2008). Although the primary sources such as biomass burning may be important for WSOC loadings , it is suggested that a major fraction of WSOC is from secondary organic aerosol (SOA) formation (Aggarwal and Kawamura, 2009;Kondo et al, 2007).…”