Secondary particle formation and evidence of heterogeneous chemistry during a wood smoke episode in Texas

Abstract

[1] To evaluate the impact of regional wildfires in east Texas on fine particulate matter concentration and composition, source apportionment calculations were performed on a set of samples collected at three sites in Houston during a wood smoke episode. Separately, samples collected at the same sites on days not influenced by wood smoke, were analyzed for comparison. The analysis of the data collected on non-wood smoke episode days indicated that the major contributors to PM 2.5 mass were secondary sulfate, diesel and gasoline powered vehicles, other organics (difference between the measured organic mass by carbon (OMC) and the sum of the primary OC source contributions), wood combustion and meat cooking. Secondary sulfate (not apportioned to a primary source) represented almost 100% of the sulfate measured whereas primary sources were found to account for the majority of the measured organic carbon at three sites (64-69%). On the wood smoke episode days, major sources of PM 2.5 were found to be the same as on the days without wood smoke, except for the contribution of the meat cooking source, which became insignificant on the wood smoke episode days. The contribution of the wood combustion source increased by an average of 200% at all sites on wood smoke episode days, whereas the contributions of other primary sources did not increase significantly during the wood smoke episode. PM 2.5 mass almost doubled during the wood smoke episode, largely because of the contributions of the secondary sources. The mass concentrations of secondary sulfate and organics not attributed to primary sources increased 68% and 228% at each site, respectively, during the wood smoke episode. The increase in the contributions of secondary sulfate aerosols during the wood smoke episode was examined using a 3-D photochemical grid model. The simulations, together with ambient data, indicated that the increases in sulfate concentrations observed during this wood smoke episode were consistent with heterogeneous/surface reactions on wood smoke particles.

Transport of Atmospheric Fine Particulate Matter: Part 1—Findings from Recent Field Programs on the Extent of Regional Transport within North America

“…Buzcu et al 33 and Nopmongcol and Allen 35 also report very high sulfate concentrations during the fire episode that occurred during the Supersite intensive measurement period and concluded that the fire particles were catalyzing the formation of additional sulfate. Data emerging from other field programs support the hypothesis that fire particles catalyze soot formation.…”

“…Wood smoke was found to be highly episodic as a source, and the strength of the source was most dependent on fires occurring within a several-hundred-kilometer radius of Houston. Junquera et al 34 estimated emissions from the fires during the Supersite intensive measurement period considered by Buzcu et al 33 and found that, during periods of intense fire activity, fires can become the dominant primary source of PM 2.5 in the region.…”

“…However, although average compositions show seasonal and spatial homogeneity, individual days can show great variability from mean values. 30 Buzcu et al 33 have performed source allocations for the PM 2.5 at Houston locations that are both typically urban and industrial source dominated. Organic molecular tracers and chemical mass balances were used as the source apportionment tools.…”

Review of Recent Advances in Detection of Organic Markers in Fine Particulate Matter and Their Use for Source Apportionment

“…Recently, CMB and PMF approaches were used to estimate the source contributions to PM 2.5 levels with an organic marker compound and it was found that the impact of direct emissions from biomass combustion can be isolated from the effects of primary emissions on secondary sulfate formation. 213 The application of PMF to the source apportionment of carbonaceous material in the atmosphere will be examined using the results from four recent studies. These studies have different objectives and, hence, different protocols and outcomes.…”

Fine Particulate Matter Emissions Inventories: Comparisons of Emissions Estimates with Observations from Recent Field Programs

“…Estimates based on measurements of levoglucosan (a molecular marker of wood smoke) and on estimates of fire acreage and land cover burned are consistent in indicating that wildfires and controlled burns of biomass contribute of order 1-2% of the annual average total PM 2.5 mass in the Houston-Galveston area. 75,77,116 • Geological sources of PM 2.5 (dust) are a relatively minor contributor to total PM 2.5 mass in the urban Houston-Galveston, TX, area. Buzcu et al 116 and Yue and Fraser 117 have estimated that road dust accounted for an average of 0.3 g/m 3 of PM 2.5 mass (2% of total PM 2.5 mass) in August and September 2000, at a ship channel area site (Houston Regional Monitoring Site No.…”