Budget of organic carbon in a polluted atmosphere: Results from the New England Air Quality Study in 2002

Abstract

[1] An extensive set of volatile organic compounds (VOCs) and particulate organic matter (POM) was measured in polluted air during the New England Air Quality Study in 2002. Using VOC ratios, the photochemical age of the sampled air masses was estimated. This approach was validated (1) by comparing the observed rates at which VOCs were removed from the atmosphere with the rates expected from OH oxidation, (2) by comparing the VOC emission ratios inferred from the data with the average composition of urban air, and (3) by the ability to describe the increase of an alkyl nitrate with time in terms of the chemical kinetics. A large part of the variability observed for oxygenated VOCs (OVOCs) and POM could be explained by a description that includes the removal of the primary anthropogenic emissions, the formation and removal of secondary anthropogenic species, and a biogenic contribution parameterized by the emissions of isoprene. The OVOC sources determined from the data are compared with the available literature, and a satisfactory agreement is obtained. The observed sub-mm POM was highly correlated with secondary anthropogenic gas-phase species, strongly suggesting that the POM was from secondary anthropogenic sources. The results are used to describe the speciation and total mass of gas-and particle-phase organic carbon as a function of the photochemical age of an urban air mass. Shortly after emission the organic carbon mass is dominated by primary VOCs, while after two days the dominant contribution is from OVOCs and sub-mm POM. The total measured organic carbon mass decreased by about 40% over the course of two days. The increase in sub-mm POM could not be explained by the removal of aromatic precursors alone, suggesting that other species must have contributed and/or that the mechanism for POM formation is more efficient than previously assumed.Citation: de Gouw, J. A., et al. (2005), Budget of organic carbon in a polluted atmosphere: Results from the New England Air

Organic Aerosols in the Earth’s Atmosphere

“…By normalizing OA to an inert combustion tracer such as CO or acetylene, the variability due to emissions and transport can be accounted for to a certain extent (8). Enhancement ratios of OA versus CO are denoted as ∆OA/∆CO, where ∆ indicates the excess amount over the background concentration.…”

“…Two studies argued that all these findings can be reconciled if biogenic SOA formation is more efficient in polluted air (8,17). In that scenario, the organic carbon is biogenic, but the OA correlates with anthropogenic tracers.…”

“…Nevertheless, several recent studies found that OA was well correlated with tracers of urban pollution such as CO, acetylene (C 2 H 2 ), iso-propylnitrate, and odd oxygen (O 3 + NO 2 ) (8,(14)(15)(16)(17), suggesting that the influence of urban emissions may be larger than previously recognized. These studies showed that the good correlation is not due to emissions of POA, but to a rapid growth of SOA in urban air that overwhelms the direct POA emissions within a few hours of photochemical processing (8,(18)(19)(20).The atmospheric variability in OA is due to the spatial distribution of emissions, transport, chemical transformation, and removal by deposition. By normalizing OA to an inert combustion tracer such as CO or acetylene, the variability due to emissions and transport can be accounted for to a certain extent (8).…”

A simplified description of the evolution of organic aerosol composition in the atmosphere

“…However, models are generally unsuccessful in reproducing the observed magnitudes and variability of these particles [Capes et al, 2009;de Gouw et al, 2005;Heald et al, 2005Heald et al, , 2006Johnson et al, 2006;Kleinman et al, 2008;Volkamer et al, 2006]. Such difficulties likely arise from complexity in the sources (including both primary combustion emissions, POA, and secondary production SOA), composition, and chemistry of OA.…”

Particulate Matter: A Strategic Vision for Transportation-Related Research

“…Recent research suggests that motor-vehicle or other anthropogenic sources may be a greater contributor to SOAs than predicted by current modeling (20). From an air-quality management perspective, uncertainty about SOA sources is a key problem, because SIPs must address important sources to reduce PM concentrations.…”