Surprisingly small HONO emissions from snow surfaces at Browning Pass, Antarctica

Atmospheric Chemistry and Physics (Impact Factor: 5.51). 07/2006; DOI: 10.5194/acp-6-2569-2006
Source: DOAJ

ABSTRACT Measured Fluxes of nitrous acid at Browning Pass, Antarctica were very low, despite conditions that are generally understood as favorable for HONO emissions, including: acidic snow surfaces, an abundance of NO3- anions in the snow surface, and abundant UV light for NO3- photolysis. Photochemical modeling suggests noon time HONO fluxes of 5–10 nmol m-2 h-1; the measured fluxes, however, were close to zero throughout the campaign. The location and state of NO3- in snow is crucial to its reactivity. The analysis of soluble mineral ions in snow reveals that the NO3- ion is probably present in aged snows as NaNO3. This is peculiar to our study site, and we suggest that this may affect the photochemical reactivity of NO3-, by preventing the release of products, or providing a reactive medium for newly formed HONO. In fresh snow, the NO3- ion is probably present as dissolved or adsorbed HNO3 and yet, no HONO emissions were observed. We speculate that HONO formation from NO3- photolysis may involve electron transfer reactions of NO2 from photosensitized organics and that fresh snows at our site had insufficient concentrations of adequate organic compounds to favor this reaction.

Download full-text


Available from: Florent Domine, Jun 24, 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report on the development of an optical instrument based on incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) for simultaneous open-path measurements of nitrous acid (HONO) and nitrogen dioxide (NO2) in ambient air using a UV light emitting diode operating at ∼366 nm. Detection limits of ∼430 pptv for HONO and ∼1 ppbv for NO2 were achieved with an optimum acquisition time of 90 s, determined by an Allan variance analysis. Based on a 1.85 m long high optical finesse open-path cavity, the effective optical path length of 2.8 km was realized in aerosol-free samples or in an urban environment at modest aerosol levels. Such a kilometer long optical absorption is comparable to that achieved in the well established differential optical absorption spectroscopy (DOAS) technology while keeping the instrument very compact. Open-path detection configuration allows one to avoid absorption cell wall losses and sampling induced artifacts. The demonstrated sensitivity and specificity shows high potential of this cost-effective and compact infrastructure for future field applications with high spatial resolution.
    Applied Physics B 02/2011; 106(2). DOI:10.1007/s00340-011-4818-3 · 1.63 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Nitrogen oxides (NO + NO2) and HONO are among the most reactive species in the polar boundary layer. About a decade ago, the discovery of photochemical production of NOx and HONO in the polar snowpack forced us to consider the role of snowpack emissions to understand the composition of the polar boundary layer. Here we present evidence that NOx and HONO can be emitted by the snowpack to the polar boundary layer in the absence of sunlight. NOx and HONO fluxes were measured at Ny Alesund, Svalbard (79∘N) from mid February (no sunlight) to late April (24 h sunlight). Values were mostly positive (i.e. species transferred from snow to atmosphere) and up to 800 and 120 nmol m-2 h-1, respectively, with the highest values observed in the near absence of sunlight. Mineral ions in surface snow were also analyzed continuously, and snow chemistry data led us to suspect that bacteria were involved in those emissions. The measurements of nitrate isotopic data (δ15N and Δ17O) confirmed that a large fraction of nitrate in most snow layers was not of atmospheric origin, and our interpretation is that is was produced from ammonium by nitrifying bacteria. NO2- is an intermediate in nitrification, and can lead to NO emission by bacteria. NO can be rapidly oxidized to NO2 by ozone in the snowpack. Physical release of HONO from NO2- by the snow also takes place. We therefore suggest that microbial activity in cold snowpacks can lead to the release of significant amounts of reactive species, and deserves consideration in the understanding of polar boundary chemistry and of polar snow chemistry.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Photochemical production of NOx and HONO from surface snow can significantly impact the NOx, OH, and O3 budgets in the overlying atmosphere. NOx production is driven by the solar photolysis of NO3− within or at the surface of snowpacks. HONO, however, is a secondary species that involves H-atom transfer between natural donors and photogenerated NO2. Here we investigate the mechanism of HONO generation in snowpacks by exploring how its emissions respond to on-and-off illumination and temperature cycles, and to the addition of various snow dopants. The presence of humic substances within or at the surface of the snowpack significantly enhances, and may be an essential requisite for HONO production. Emission fluxes of NO, NO2, and HONO from snow surfaces were measured under controlled temperature, ozone mixing ratio and actinic flux conditions. We used natural mid-latitude surface snow as the snow substrate. Their combined peak emission fluxes reached up to ~3 × 10^10 molecules cm^−2 s^−1, ~10^3 times larger than typical emissions from polar snowpacks. Less than 1% of available N was released in these experiments. We report significant post-irradiation HONO emissions from the snow. Present results indicate a strong, direct correlation between HONO emissions and the HULIS (humic-like substances) content of the snow surface.
    Environmental Research Letters 10/2008; 3(4). DOI:10.1088/1748-9326/3/4/045005 · 4.09 Impact Factor