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

Atmospheric Chemistry and Physics (Impact Factor: 5.05). 07/2006; 6(9). DOI: 10.5194/acp-6-2569-2006
Source: DOAJ


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,
8 Reads
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Environmental context. Nitrous acid (HNO2) is an important source of the hydroxyl radical (OH•), the most important daytime oxidising species that contributes to the formation of ozone as well as of other secondary pollutants in the troposphere. Understanding the sources and sinks of HNO2 is of crucial interest for accurately modelling the chemical composition of the troposphere and predicting future trace gas concentrations. Abstract. Nitrous acid and several other atmospheric components and variables were continuously measured during complex field experiments at seven different suburban and rural sites in Europe. HNO2 is mainly formed by heterogeneous processes and is often accumulated in the nighttime boundary layer. Our results confirm that the photolysis of HNO2 is an important source of the hydroxyl radical, not only in the early morning hours but also throughout the entire day, and is often comparable with the contribution of ozone and formaldehyde photolysis. At all research sites unexpectedly high HNO2 mixing ratios were observed during the daytime (up to several hundred ppt, or pmol mol–1). Moreover, surprisingly, the HNO2 mixing ratio at the three mountain sites often showed a broad maximum or several distinct peaks at midday and lower mixing ratios during the night. Assuming a quickly established photo-equilibrium between the known significant gas phase reactions, only a few ppt HNO2 should be present around noon. The ratio of known sources to sinks indicates a missing daytime HNO2 source of 160–2600 ppt h–1 to make up the balance. Based on these values and on production mechanisms proposed in the literature we hypothesise that the daytime mixing ratio levels may only be explained by a fast electron transfer onto adsorbed NO2.
    Environmental Chemistry 01/2007; 4(4). DOI:10.1071/EN07023 · 2.51 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the first measurements of the oxygen isotope anomaly of atmospheric inorganic nitrate from the Arctic. Nitrate samples and complementary data were collected at Alert, Nunavut, Canada (82°30 ' N, 62°19 ' W) in spring 2004. Covering the polar sunrise period, characterized by the occurrence of severe boundary layer ozone depletion events (ODEs), our data show a significant correlation between the variations of atmospheric ozone (O<sub>3</sub>) mixing ratios and ?<sup>17</sup>O of nitrate (?<sup>17</sup>O(NO<sup>-</sup><sub>3</sub>)). This relationship can be expressed as: ?<sup>17</sup>O(NO<sup>-</sup><sub>3</sub>)/‰, =(0.15±0.03)×O<sub>3</sub>/(nmol mol<sup>–1</sup>)+(29.7±0.7), with R<sup>2</sup>=0.70(n=12), for ?<sup>17</sup>O(NO<sup>-</sup><sub>3</sub>) ranging between 29 and 35 ‰. We derive mass-balance equations from chemical reactions operating in the Arctic boundary layer, that describe the evolution of ?<sup>17</sup>O(NO<sup>-</sup><sub>3</sub>) as a function of the concentrations of reactive species and their isotopic characteristics. Changes in the relative importance of O<sub>3</sub>, RO<sub>2</sub> and BrO in the oxidation of NO during ODEs, and the large isotope anomalies of O<sub>3</sub> and BrO, are the driving force for the variability in the measured ?<sup>17</sup>O(NO<sup>-</sup><sub>3</sub>) . BrONO<sub>2</sub> hydrolysis is found to be a dominant source of nitrate in the Arctic boundary layer, in agreement with recent modeling studies.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 03/2007; 7(5):1451-1469. DOI:10.5194/acp-7-1451-2007 · 5.05 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The films coating urban impervious surfaces have been found to be comprised of about 7% inorganic nitrate and approximately 10% organic compounds (by mass). A simple steady-state analysis of the lifetime of the nitrate in the film suggests the existence of a loss process(es) in addition to washout by rainfall. We show here that gas-phase nitric acid can be taken up in organic films and lower the film pH. Photolysis of nitrated films using actinic illumination causes loss both of protons and of nitrate anion. We argue that this is possibly due to a combination of direct and indirect (photosensitized) photochemistry involving nitrate ions, yielding gas-phase HONO and/or NO2.
    Environmental Science and Technology 07/2007; 41(11):3898-903. DOI:10.1021/es062044z · 5.33 Impact Factor
Show more