Characteristics of atmospheric organic and elemental carbon particle concentrations in Los Angeles

Abstract

A fine particle air monitoring network was operated in the Los Anaeles area durin& 1982.It was found that carbonaceous aerosols accounted for typically 4~ of total fine particle mass loadings at most monitoring sites.The ratio of total carbon (TC) to elemental carbon (EC) in ambient samples and in primary source emissions was examined as an indica tor of the extent of secondary organic aerosol formation. It was found that TC to EC ratios at all sites on average are no higher than recent estimates of the TC to EC ratio in primary source emissions. There is little evidence of the sustained summer peak in the ratio of TC to EC that one misht expect if greatly enhanced secondary oraanics production occurs during the photochemical smog season.The TC to EC ratio does rise by the time that air masses reach the prevailing downwind edse of the air basin as would be expected if secondary organics are being formed during air parcel transport. but the extent of that increase is modest. These results suggest that primary particulate carbon emissions were the principal contributor to long-term average fine aerosol carbon concentrations in the Los Angeles area during 1982 . If the overwhelming majority of aerosol carbon was formed in the atmosphere as a secondary product of photochemical reactions* then controls on direct emissions of carbon particles from sources might have little effect on urban air quality.The present paper is the first of a series designed to describe methods for achieving deliberate control of urban fine carbon particle concentrations. In this work* the approach used to acquire an air quality model verification data set for organic and elemental carbon concentrations will be described. This method will be demonstrated in Los Angeles* and key characteristics of Los Angeles carbonaceous aerosol air quality will be defined. The spatial and temporal distribution of aerosol carbon concentrations over an entire annual cycle will be described. The geographic areas that experience the highest aerosol carbon concentrations will be identified and related to source density and pollutant transport patterns. The ratio of total carbon to elemental carbon in the atmosphere will be examined as an indicator of the extent of secondary organic carbon aerosol formation. In subsequent papers* air quality models will be tested against this data set. The importance of major source types to observed aerosol carbon air quality will be quantified through that modeling effort. Mathematical programming methods for defining the most attractive approaches to aerosol carbon control then will be illustrated* using the results of the air quality modeling study. The ambient sampling equipment constructed for use in this study is illustrated in Figure 2, and was designed to obtain a near mass balance on the chemically identifiable portion of the atmospheric fine particle loading. Ambient air at a flow rate of 25.9 fpm was drawn through an AIHL cyclone designed to remove particles with aerodynamic diaaeter laraer than 2.1 pa. 'The air flow ...

Measurements of aerosol size‐resolved hygroscopicity at sub and supermicron sizes

“…On the other hand, the composition of the fire aerosol itself suggests a reduced hygroscopicity, being $80% organic by mass, much higher than that typical for Los Angeles pollution [cf. Gray et al, 1986], though we have no chemical measurements on the 18th to confirm this for our specific case. Interestingly, our fire spectrum is consistent with recent measurements by Rissler et al [2004] on fire plume aerosols in Amazonia (shown in Figure 4), suggesting that such low hygroscopicity for fire aerosols may be common.…”

Source Apportionment: Findings from the U.S. Supersites Program

“…35,102,103 It accounts for OC not associated with any other sources and leads to results similar to those of Schauer and Cass. 101 A tracer solution CMB was tested by Gray et al 104 using EC as the marker for primary source types. 105 Assuming that primary OC and EC concentrations are correlated at a specific location because they have common sources, SOA is estimated as:…”

Characterization of urban and rural organic particulate in the Lower Fraser Valley using two Aerodyne Aerosol Mass Spectrometers

“…Understanding the composition of atmospheric aerosol particles is necessary for identifying their sources and predicting their effect on various atmospheric processes. Although organic compounds typically account for 10-70% of the total dry fine particle mass in the atmosphere (Gray et al, 1986;Middlebrook et al, 1998), organic PM concentrations, composition and formation mechanisms are not well understood, particularly in relation to the other major fine particle constituents, i.e. sulphate and nitrate compounds.…”

“…These include the use of tracer compounds for either the primary or the secondary OC (Gray et al, 1986;Turpin and Huntzicker, 1991), the use of models describing the formation of secondary OC (Pandis et al, 1992) and the use of models describing the emission and dispersion of primary OC (Harley and Cass, 1995).…”