Heue, Klaus-Peter and Riede, H. and Walter, D. and Brenninkmeijer, C. A. M. and Wagner, T. and Frieß, U. and Platt, Ulrich and Zahn, A. and Stratmann, Greta and Ziereis, Helmut (2014) CARIBIC DOAS observations of nitrous acid and formaldehyde in a large convective cloud. Atmospheric Chemistry and Physics, 14, pp. 6621-6642. Copernicus Publication. DOI: 10.5194/acp-14-6621-2014. ISSN 1680-7316.
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The chemistry in large thunderstorm clouds is influenced by local lightning-NOx production and uplift of boundary layer air. Under these circumstances trace gases like nitrous acid (HONO) or formaldehyde (HCHO) are expected to be formed or to reach the tropopause region. However, up to now only few observations of HONO at this altitude have been reported. Here we report on a case study where enhancements in HONO, HCHO and nitrogen oxides (NOx) were observed by the CARIBIC flying laboratory (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container). The event took place in a convective system over the Caribbean Sea in August 2011. Inside the cloud the light path reaches up to 100 km. Therefore the DOAS instrument on CARIBIC was very sensitive to the tracers inside the cloud. Based on the enhanced slant column densities of HONO, HCHO and NO2, average mixing ratios of 37, 468 and 210 ppt, respectively, were calculated. These data represent averages for constant mixing ratios inside the cloud. However, a large dependency on the assumed profile is found; for HONO a mixing ratio of 160 ppt is retrieved if the total amount is assumed to be situated in the uppermost 2 km of the cloud. The NO in situ instrument measured peaks up to 5 ppb NO inside the cloud; the background in the cloud was about 1.3 ppb, and hence clearly above the average outside the cloud (≈ 150 ppt). The high variability and the fact that the enhancements were observed over a pristine marine area led to the conclusion that, in all likelihood, the high NO concentrations were caused by lighting. This assumption is supported by the number of flashes that the World Wide Lightning Location Network (WWLLN) counted in this area before and during the overpass. The chemical box model CAABA is used to estimate the NO and HCHO source strengths which are necessary to explain our measurements. For NO a source strength of 10 × 109 molec cm−2 s−1 km−1 is found, which corresponds to the lightning activity as observed by the World Wide Lightning Location network, and lightning emissions of 5 × 1025 NO molec flash−1 (2.3–6.4 × 1025). The uncertainties are determined by a change of the input parameters in the box model, the cloud top height and the flash density. The emission rate per flash is scaled up to a global scale and 1.9 (1.4–2.5) tg N a−1 is estimated. The HCHO updraught is of the order of 120 × 109 molec cm−2 s−1 km−1. Also isoprene and CH3OOH as possible HCHO sources are discussed.
|Title:||CARIBIC DOAS observations of nitrous acid and formaldehyde in a large convective cloud|
|Date:||1 July 2014|
|Journal or Publication Title:||Atmospheric Chemistry and Physics|
|In Open Access:||Yes|
|In ISI Web of Science:||Yes|
|Page Range:||pp. 6621-6642|
|Keywords:||DOAS, nitrous acid, formaldehyde, convective cloud, CARIBIC|
|HGF - Research field:||Aeronautics, Space and Transport|
|HGF - Program:||Aeronautics|
|HGF - Program Themes:||air traffic management and operations|
|DLR - Research area:||Aeronautics|
|DLR - Program:||Air Traffic Management and Operation|
|DLR - Research theme (Project):||Climate, Weather and Environment|
|Institutes and Institutions:||Institute of Atmospheric Physics > Atmospheric Trace Species|
|Deposited By:||Greta Stratmann|
|Deposited On:||10 Jul 2014 10:35|
|Last Modified:||10 Jul 2014 10:35|
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