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  CARIBIC DOAS observations of nitrous acid and formaldehyde in a large convective cloud

Heue, K.-P., Riede, H., Walter, D., Brenninkmeijer, C. A. M., Wagner, T., Frieß, U., et al. (2014). CARIBIC DOAS observations of nitrous acid and formaldehyde in a large convective cloud. Atmospheric Chemistry and Physics, 14(13), 6621-6642. doi:10.5194/acp-14-6621-2014.

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Heue, K.-P.1, Author              
Riede, H.1, Author              
Walter, D.1, Author              
Brenninkmeijer, C. A. M.1, Author              
Wagner, T.2, Author              
Frieß, U.3, Author
Platt, U.3, Author
Zahn, A.3, Author
Stratmann, G.3, Author
Ziereis, H.3, Author
1Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society, ou_1826285              
2Satellite Remote Sensing, Max Planck Institute for Chemistry, Max Planck Society, ou_1826293              
3external, ou_persistent22              


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 Abstract: 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 (approximate to 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 x 10(9) 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 x 10(25) NO molec flash(-1) (2.3-6.4 x 10(25)). 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) tgNa(-1) is estimated. The HCHO updraught is of the order of 120 x 10(9) molec cm(-2) s(-1) km(-1). Also isoprene and CH3OOH as possible HCHO sources are discussed.


 Dates: 2014
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: ISI: 000339244600009
DOI: 10.5194/acp-14-6621-2014
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Title: Atmospheric Chemistry and Physics
Source Genre: Journal
Publ. Info: Katlenburg-Lindau, Germany : European Geosciences Union
Pages: - Volume / Issue: 14 (13) Sequence Number: - Start / End Page: 6621 - 6642 Identifier: ISSN: 1680-7316
CoNE: https://pure.mpg.de/cone/journals/resource/111030403014016