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  • 1
    Electronic Resource
    Electronic Resource
    Is the Arctic Surface Layer a Source and Sink of NOx in Winter/Spring? (2000)
    Springer
    Journal of atmospheric chemistry 36 (2000), S. 1-22 
    Details
    ISSN: 1573-0662
    Keywords: active nitrogen ; ozone ; radicals ; snow chemistry ; Arctic ; surface layer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Measurements of NOx (NO +NO2) and the sum of reactive nitrogenconstituents, NOy, were made near the surface atAlert (82.5°N), Canada during March and April1998. In early March when solar insolation was absentor very low, NOx mixing ratios were frequentlynear zero. After polar sunrise when the sun was abovethe horizon for much or all of the day a diurnalvariation in NOx and NOy was observed withamplitudes as large as 30–40 pptv. The source ofactive nitrogen is attributed to release from the snowsurface by a process that is apparently sensitized bysunlight. If the source from the snowpack is a largescale feature of the Arctic then the diurnal trendsalso require a competing process for removal to thesurface. From the diurnal change in the NO/NO2ratio, mid-April mixing ratios for the sum of peroxyand halogen oxide radicals of ≤10 pptv werederived for periods when ozone mixing ratios were inthe normal range of 30–50 ppbv. Mid-day ozoneproduction and loss rates with the active nitrogensource were estimated to be ∼1–2 ppbv/day and in nearbalance. NOy mixing ratios which averaged only295±66 pptv do not support a large accumulation inthe high Arctic surface layer in the winter and springof 1998. The small abundance of NOy relative tothe elevated mixing ratios of other long-livedanthropogenic constituents requires that reactivenitrogen be removed to the surface during transport toor during residence within the high Arctic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006301029874
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    Paper (German National Licenses)
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  • 2
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    Nitrous acid (HONO) during polar spring in Barrow, Alaska: A net source of OH radicals? (2011)
    Wiley-Blackwell
    Details
    Publication Date: 2011-12-23
    Description: HONO was measured by a LOPAP instrument (LOng Path Absorption Photometer) for one month during the OASIS spring 2009 campaign in Barrow, Alaska. HONO concentrations between ≤ 0.4 pptv (DL) and ∼500 pptv were measured. The very high concentrations observed on several days were caused by local direct emissions and were highly correlated with the NOx and CO data. When only “clean days” were considered, average HONO concentrations varied between ≤ 0.4 - 10 pptv. Average HONO/NOx and HONO/NOy ratios of ∼6% and ∼1% were observed, respectively, in good agreement with other remote LOPAP measurement data, but lower than measured in most other polar regions by other methods. The strong correlation between sharp peaks of OH and HONO during daytime, which was not observed for any other measured radical precursor, suggested that HONO photolysis was a major source of OH radicals in Barrow. This was supported by calculated net OH radical production by HONO and O3 photolysis for which the contribution of O3 (2%) could be neglected compared to that of HONO (98%). A net extra HONO/OH source necessary to explain elevated HONO levels during daytime of up to 90 pptv/h was determined, which was highly correlated with the actinic flux. Accordingly, a photochemical HONO source is proposed here, in good agreement with recent studies. From the higher correlation of the net HONO source with JNO2 and [NO2] compared to JO(1D) and [NO3−], photosensitized conversion of NO2 on humic acid containing snow surfaces may be a more likely source of HONO in the polar atmosphere of Barrow than nitrate photolysis.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 3
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    Tropospheric SF6: Age of Air from the Northern Hemisphere Mid-latitude Surface (2013)
    Wiley-Blackwell
    Details
    Publication Date: 2013-09-21
    Description: [1]  Observations of SF 6 are used to quantify the mean time since air was in (“mean age” from) the northern hemisphere (NH) mid-latitude surface layer. The mean age is a fundamental property of tropospheric transport that can be used in theoretical studies and used to evaluate transport in comprehensive models. Comparisons of simulated SF 6 and an idealized clock tracer confirm that the time lag between the SF 6 mixing ratio at a given location and the NH mid-latitude surface provides an accurate estimate of the mean age. The ages calculated from surface SF 6 measurements show large meridional gradients in the tropics but weak gradients in the extratropics, with near zero ages at the surface north of 30 o N and ages around 1.4 yr south of 30 o S. Aircraft measurements show weak vertical age gradients in the lower-middle troposphere, with only slight increases of age with height in the NH and slight decreases with height in the SH. There are large seasonal variations in the age at tropical stations (annual amplitudes around 0.5-1.0 yr), with younger ages during northern winter, but only weak seasonal variations at higher latitudes. The seasonality and interannual variations in the tropics and southern hemisphere are related to changes in locations of tropical convection. There is qualitative agreement, in both spatial and temporal variations, between the simulated ages and observations. The model ages tend to be older than observed, with differences of ~0.2 yr in the northern hemisphere upper troposphere and throughout the southern hemisphere troposphere.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 4
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    Constraining surface carbon fluxes using in situ measurements of carbonyl sulfide and carbon dioxide (2014)
    Wiley-Blackwell
    Details
    Publication Date: 2014-01-23
    Description: [1]  Understanding the processes that control the terrestrial exchange of carbon is critical for assessing atmospheric CO 2 budgets. Carbonyl sulfide (COS) is taken up by vegetation during photosynthesis following a pathway that mirrors CO 2 , but has a small or non-existent emission component. This tracer could thus provide a means to separate photosynthetic and respiration fluxes. We present field measurements of COS and CO 2 mixing ratios made during the summer of 2012 in a forest, senescent grassland and riparian ecosystem using a laser absorption spectrometer installed in a mobile trailer. Measurements of leaf fluxes with a branch-bag gas-exchange system were made across species from 10 genera of trees, and soil fluxes were measured with a flow-through chamber across a number of soil types. These data provide an extensive characterization of surface COS fluxes and show: (1) the existence of a narrow normalized daytime uptake ratio of COS to CO 2 across vascular plant species of 1.7, providing critical information for the application of COS to estimate photosynthetic CO 2 fluxes and (2) a temperature-dependent normalized uptake ratio of COS to CO 2 from soils. Significant nighttime uptake of COS was observed in broad-leafed species and revealed active stomatal opening hours prior to sunrise. Joint measurements of ambient near-surface COS and CO 2 concentrations are used here alongside the flux measurements to partition the relative influence that leaf and soil fluxes and entrainment of air from above have on the surface carbon budget. The time-dependent co-variation of COS and CO 2 in the ambient surface air sheds light on the dominant processes influencing the surface carbon budget in ways that cannot be done with measurements of only CO 2 . The results provide a number of critical constraints on the processes that control surface COS exchange, which can be used to diagnose the robustness of global models that are beginningto use COS to constrain terrestrial carbon exchange.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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