High concentrations and photochemical fate of oxygenated hydrocarbons in the global troposphere

Abstract. Measurement of NO 2 at low concentrations (tens of ppts) is non-trivial. A variety of techniques exist, with the conversion of NO 2 into NO followed by chemiluminescent detection of NO being prevalent. Historically this conversion has used a catalytic approach (molybdenum); however, this has been plagued with interferences. More recently, photolytic conversion based on UV-LED irradiation of a reaction cell has been used. Although this appears to be robust there have been a range of observations in low-NO x environments which have measured higher NO 2 concentrations than might be expected from steady-state analysis of simultaneously measured NO, O 3 , j NO 2 , etc. A range of explanations exist in the literature, most of which focus on an unknown and unmeasured "compound X" that is able to convert NO to NO 2 selectively. Here we explore in the laboratory the interference on the photolytic NO 2 measurements from the thermal decomposition of peroxyacetyl nitrate (PAN) within the photolysis cell. We find that approximately 5 % of the PAN decomposes within the instrument, providing a potentially significant interference. We parameterize the decomposition in terms of the temperature of the light source, the ambient temperature, and a mixing timescale (∼ 0.4 s for our instrument) and expand the parametric analysis to other atmospheric compounds that decompose readily to NO 2 (HO 2 NO 2 , N 2 O 5 , CH 3 O 2 NO 2 , IONO 2 , BrONO 2 , higher PANs). We apply these parameters to the output of a global atmospheric model (GEOS-Chem) to investigate the global impact of this interference on (1) the NO 2 measurements and (2) the NO 2 : NO ratio, i.e. the Leighton relationship. We find that there are significant interferences in cold regions with low NO x concentrations such as the Antarctic, the remote Southern Hemisphere, and the upper troposphere. Although this interference is likely instrument-specific, the thermal decomposition to NO 2 within the instrument's photolysis cell could give an at least partial explanation for the anomalously high NO 2 that has been reported in remote regions. The interference can be minimized by better instrument characterization, coupled to instrumental designs which reduce the heating within the cell, thus simplifying interpretation of data from remote locations.

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“…Reactions (R9)-(R13) show the reaction sequence by which PAN is formed by acetone photolysis (Singh et al, 1995).…”

Section: Pan Preparationmentioning

confidence: 99%

Interferences in photolytic NO<sub>2</sub> measurements: explanation for an apparent missing oxidant?

et al. 2016

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“…[2] Oxygenated volatile organic compounds (OVOCs) including methanol, acetaldehyde, and acetone are ubiquitous in the atmosphere [e.g., Lewis et al, 2005;Singh et al, 1995Singh et al, , 2003 where they affect the tropospheric ozone budget, are precursors to peroxy acetyl nitrate and, in the remote marine environment, represent a significant sink of the hydroxyl radical and thus the oxidizing capacity of the lower atmosphere [Folkins and Chatfield, 2000;Lewis et al, 2005]. In remote marine air, oceanic sources and sinks of OVOCs are assumed to be significant in controlling air concentrations [Read et al, 2012], although the magnitude and direction of the OVOC air-sea fluxes are a matter of debate [Beale et al, 2013;Carpenter et al, 2004;Heikes et al, 2002;Marandino et al, 2005;Taddei et al, 2009;Williams et al, 2004] largely as a consequence of extremely limited OVOC measurements in oceanic surface waters.…”

Section: Introductionmentioning

confidence: 99%

Production of methanol, acetaldehyde, and acetone in the Atlantic Ocean

Dixon

Beale

2013

Geophysical Research Letters

112

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[1] The biogeochemistry of oxygenated volatile organic compounds (OVOCs) like methanol, acetaldehyde, and acetone in marine waters is poorly understood. We report the first in situ gross production rates for methanol, acetaldehyde, and acetone of 49-103, 25-98, and 2-26 nmol L À1 d À1 over contrasting areas of marine productivity, including oligotrophic gyres and eutrophic upwellings. Photochemical production estimates are mostly negligible for methanol, up to 68% for acetaldehyde and up to 100% of gross production rates for acetone. Microbial surface OVOC oxidation to CO 2 accounts for between 10-50% and 0.5-13% of the methanol and acetone losses, respectively, but largely control acetaldehyde concentrations (49-100%). Biological lifetimes in a coastal upwelling vary between ≤1 day for acetaldehyde, to approximately 7 days for methanol and up to~80 days for acetone. In open oceanic environments, the lifetime of acetaldehyde ranges between 2 and 5 h, compared to 10-26 days for methanol and 5-55 days for acetone.

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“…Consequently their mixing ratios and fluxes, as well as their global budgets, have been widely investigated (Jacob et al, 2002;Seco et al, 2007;Kumar et al, 2011;Laffineur et al, 2012). The short-chain OVOCs with high activity, such as methanol, ethanol, formaldehyde, acetaldehyde, acetone and 2-methyl-3-buten-2-ol, can sequester reactive nitrogen to form peroxyacetyl nitrate and are easily photolyzed to produce free radicals such as HOx (Arnold et al, 1986;Singh et al, 1995;Atkinson, 2000), and thus influence the oxidizing capacity and ozone-forming potential of the atmosphere and contribute significantly to the formation of secondary organic aerosols (Singh et al, 1995;Seco et al, 2007;Kumar et al, 2011). On the local scale, some OVOCs are primary irritants and offensive odor pollutants with very low sensory thresholds (Devos et al, 1990; Table 1), and their emission and presence in ambient air are widely regulated.…”

Section: Introductionmentioning

confidence: 99%

Emission of oxygenated volatile organic compounds (OVOCs) during the aerobic decomposition of orange wastes

Wang

2015

Journal of Environmental Sciences

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High concentrations and photochemical fate of oxygenated hydrocarbons in the global troposphere

Cited by 618 publications

References 21 publications

Interferences in photolytic NO<sub>2</sub> measurements: explanation for an apparent missing oxidant?

Interferences in photolytic NO<sub>2</sub> measurements: explanation for an apparent missing oxidant?

Production of methanol, acetaldehyde, and acetone in the Atlantic Ocean

Emission of oxygenated volatile organic compounds (OVOCs) during the aerobic decomposition of orange wastes

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High concentrations and photochemical fate of oxygenated hydrocarbons in the global troposphere

Cited by 618 publications

References 21 publications

Interferences in photolytic NO&lt;sub&gt;2&lt;/sub&gt; measurements: explanation for an apparent missing oxidant?

Interferences in photolytic NO&lt;sub&gt;2&lt;/sub&gt; measurements: explanation for an apparent missing oxidant?

Production of methanol, acetaldehyde, and acetone in the Atlantic Ocean

Emission of oxygenated volatile organic compounds (OVOCs) during the aerobic decomposition of orange wastes

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Product

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Interferences in photolytic NO<sub>2</sub> measurements: explanation for an apparent missing oxidant?

Interferences in photolytic NO<sub>2</sub> measurements: explanation for an apparent missing oxidant?