Abstract
AbstractThe Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT) field experiment took place during late winter, 2011, at a site 33 km north of Denver, Colorado. The study included fixed‐height measurements of aerosols, soluble trace gases, and volatile organic compounds near surface level, as well as vertically resolved measurements of nitrogen oxides, aerosol composition, soluble gas‐phase acids, and halogen species from 3 to 270 m above ground level. There were 1928 individual profiles during the three‐week campaign to characterize trace gas and aerosol distributions in the lower levels of the boundary layer. Nitrate and ammonium dominated the ionic composition of aerosols and originated primarily from local or regional sources. Sulfate and organic matter were also significant and were associated primarily with longer‐range transport to the region. Aerosol chloride was associated primarily with supermicron size fractions and was always present in excess of gas‐phase chlorine compounds. The nighttime radical reservoirs, nitryl chloride, ClNO2, and nitrous acid, HONO, were both consistently present in nighttime urban air. Nitryl chloride was especially pronounced in plumes from large point sources sampled aloft at night. Nitrous acid was typically most concentrated near the ground surface and was the dominant contributor (80%) to diurnally averaged primary OH radical production in near‐surface air. Large observed mixing ratios of light alkanes, both in near‐surface air and aloft, were attributable to local emissions from oil and gas activities.
Highlights
[2] The Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT) campaign took place during winter (17 February – 14 March) 2011 at the Boulder Atmospheric
The NACHTT campaign is a unique data set for understanding wintertime atmospheric chemistry and its coupling to boundary layer dynamics since it took place in an area influenced by this complex mix of emissions and included instrumentation and vertically resolved measurements able to characterize the chemical transformations that occur during cold, dark periods
Recent observations in the western United States show that photochemical ozone production can be a severe air quality issue during wintertime in polluted mountain basins that are impacted by emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx = NO + NO2) from oil and gas exploration [Carter and Seinfeld, 2012; Schnell et al, 2009]
Summary
[2] The Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT) campaign took place during winter (17 February – 14 March) 2011 at the Boulder Atmospheric. The NACHTT campaign is a unique data set for understanding wintertime atmospheric chemistry and its coupling to boundary layer dynamics since it took place in an area influenced by this complex mix of emissions and included instrumentation and vertically resolved measurements able to characterize the chemical transformations that occur during cold, dark periods. [19] The NACHTT data set augments these prior measurements of atmospheric gas and aerosol phase chemical composition in Colorado’s Front Range Cities in several respects It is the only detailed data set that includes vertically resolved measurements of key species, including nitrogen oxides and aerosol composition through the range characteristic of the nighttime boundary layer structure.
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