Abstract
Particulate matter was measured in Conroe, Texas (~60 km north of downtown Houston, Texas) during the September 2013 DISCOVER-AQ campaign to determine the sources of particulate matter in the region. The measurement site is influenced by high biogenic emission rates as well as transport of anthropogenic pollutants from the Houston metropolitan area and is therefore an ideal location to study anthropogenic-biogenic interactions. Data from an Aerosol Chemical Speciation Monitor (ACSM) suggest that on average 64 percent of non-refractory PM1 was organic material, including a high fraction (27%–41%) of organic nitrates. There was little diurnal variation in the concentrations of ammonium sulfate; however, concentrations of organic and organic nitrate aerosol were consistently higher at night than during the day. Potential explanations for the higher organic aerosol loadings at night include changing boundary layer height, increased partitioning to the particle phase at lower temperatures, and differences between daytime and nighttime chemical processes such as nitrate radical chemistry. Positive matrix factorization was applied to the organic aerosol mass spectra measured by the ACSM and three factors were resolved—two factors representing oxygenated organic aerosol and one factor representing hydrocarbon-like organic aerosol. The factors suggest that the measured aerosol was well mixed and highly processed, consistent with the distance from the site to major aerosol sources, as well as the high photochemical activity.
Highlights
Air quality in the United States has received increased attention in recent years as regulations tighten and cities strive to reduce concentrations of airborne pollutants
In order to further explore this diurnal trend we considered PM2.5 (TEOM) measurements at four Houston area sites operated by the Texas Commission on Environmental Quality (TCEQ) [22]
Measurements were taken in Conroe, TX during 24 August–1 October 2013, as part of DISCOVER-AQ
Summary
Air quality in the United States has received increased attention in recent years as regulations tighten and cities strive to reduce concentrations of airborne pollutants. Ozone and atmospheric particulate matter (PM) are two pollutants that have received increased attention as health effects become clearer [1]. The U.S EPA recently lowered the annual NAAQS for PM2.5 (particulate matter with diameter below 2.5 μm) from 15 to 12 μgm ́3 [5]. This new annual standard brings numerous additional metropolitan regions including Houston, TX to near non-attainment for PM2.5. This underlines the importance of understanding the composition and sources of PM2.5 in these areas. Measurements can be used for source apportionment of air pollution
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