Yazar "VandenBoer, Trevor C." seçeneğine göre listele

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    New insights into atmospheric sources and sinks of isocyanic acid, HNCO, from recent urban and regional observations
    (Amer Geophysical Union, 2014) Roberts, James M.; Veres, Patrick R.; VandenBoer, Trevor C.; Warneke, Carsten; Graus, Martin; Öztürk, Fatma
    Isocyanic acid (HNCO) has only recently been measured in the ambient atmosphere, and many aspects of its atmospheric chemistry are still uncertain. HNCO was measured during three diverse field campaigns: California Nexus-Research at the Nexus of Air Quality and Climate Change (CalNex 2010) at the Pasadena ground site, Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT 2011) at the Boulder Atmospheric Observatory (BAO) in Weld County, CO, and Biofuel Crops emission of Ozone precursors intensive (BioCORN 2011), in a cornfield NW of Fort Collins, CO. Mixing ratios varied from below detection limit (similar to 0.003 ppbv) to over 1.2 ppbv during a period when agricultural burning impacted the BAO Tower site. Urban areas, such as the CalNex 2010 Pasadena site, appear to have both primary (combustion) and secondary (photochemical) sources of HNCO, 50 +/- 9%, and 33 +/- 12%, respectively, while primary sources were responsible for the large mixing ratios of HNCO observed during the wintertime NACHTT study in suburban Colorado. Isocyanic acid during the BioCORN study in rural NE Colorado was closely correlated to ozone and therefore likely photochemically produced as a secondary product from amines or formamide. The removal of HNCO from the lower atmosphere is thought to be due to deposition, as common gas phase loss processes of photolysis and reactions with hydroxyl radicals, are slow. These ambient measurements are consistent with some HNCO deposition, which was evident at night at these surface sites.
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    Understanding the role of the ground surface in HONO vertical structure: High resolution vertical profiles during NACHTT-11
    (Amer Geophysical Union, 2013) VandenBoer, Trevor C.; Brown, Steven S.; Murphy, Jennifer G.; Keene, William C.; Young, Cora J.; Öztürk, Fatma
    A negative-ion proton-transfer chemical ionization mass spectrometer was deployed on a mobile tower-mounted platform during Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT) to measure nitrous acid (HONO) in the winter of 2011. High resolution vertical profiles revealed (i) HONO gradients in nocturnal boundary layers, (ii) ground surface dominates HONO production by heterogeneous uptake of NO2, (iii) significant quantities of HONO may be deposited to the ground surface at night, (iv) daytime gradients indicative of ground HONO production or emission, and (v) an estimated surface HONO reservoir comparable or larger than integrated daytime HONO surface production. Nocturnal integrated column observations of HONO and NO2 allowed direct evaluation of nocturnal ground surface uptake coefficients for these species (gamma(NO2, surf)=2x10(-6) to 1.6x10(-5) and gamma(HONO, surf)=2x10(-5) to 2x10(-4)). A chemical model showed that the unknown source of HONO was highest in the morning, 4x10(6)moleculescm(-3)s(-1) (600pptvh(-1)), declined throughout the day, and minimized near 1x10(6)moleculescm(-3)s(-1) (165pptvh(-1)). The quantity of surface-deposited HONO was also modeled, showing that HONO deposited to the surface at night was at least 25%, and likely in excess of 100%, of the calculated unknown daytime HONO source. These results suggest that if nocturnally deposited HONO forms a conservative surface reservoir, which can be released the following day, a significant fraction of the daytime HONO source can be explained for the NACHTT observations.