Organic aerosol formation in urban and industrial plumes near Houston and Dallas, Texas

TLDR

Industrial VOC emissions and processing along the Houston ship channel lead to higher aerosol mass downwind compared to urban areas. The study measured organic aerosol in Houston and Dallas/Fort Worth urban plumes and Houston industrial plumes during TexAQS‑2006 and modeled SOA formation from VOCs using a chemical box model. A chemical box model, informed by VOC/NOx-dependent SOA yields, and a Lagrangian particle dispersion model (FLEXPART) were used to simulate SOA formation from anthropogenic and biogenic VOCs. Measurements show higher aerosol mass and ΔOA/ΔCO ratios downwind of industrial centers, with modeled SOA/CO ratios within a factor of two of observations and no significant biogenic VOC contribution to OA.

Abstract

We present measurements of organic aerosol (OA) in urban plumes from Houston and Dallas/Fort Worth as well as in industrial plumes in the Houston area during TexAQS‐2006. Consistent with the TexAQS‐2000 study, measurements show greater amount of aerosol mass downwind of the industrial centers compared to urban areas. This is likely due to higher emission and processing of volatile organic compounds (VOCs) from the industrial sources along the Houston ship channel. Comparisons of the current measurements with observations from the northeastern (NE) United States indicate that the observed ratios of the enhancement above background in OA, ΔOA, to the enhancement above background in CO, ΔCO, downwind of urban centers of Houston and Dallas/Fort Worth are within a factor of 2 of the same values in plumes from urban areas in the NE United States. In the ship channel plumes, ΔOA/ΔCO exceeds that in the urban areas by factors ranging from 1.5 to 7. We use a chemical box model to simulate secondary organic aerosol (SOA) formation from anthropogenic and biogenic VOCs in different plumes using recently reported dependencies of SOA yields on VOC/NO x ratios. Modeled SOA to CO enhancement ratios are within a factor of 2 of measurements. The increase in SOA from biogenic VOCs (BVOCs) predicted by the chemical box model as well as by a separate analysis using a Lagrangian particle dispersion model (FLEXPART) is <0.7 μ g per standard m 3 (sm −3 ). We find no evidence for a substantial influence of BVOCs on OA formation in our measurements in Houston area.