Abstract
Abstract. Peroxyacetyl nitrate (PAN) may constitute a significant fraction of reactive nitrogen in the atmosphere. Current knowledge about the biosphere–atmosphere exchange of PAN is limited, and only few studies have investigated the deposition of PAN to terrestrial ecosystems. We developed a flux measurement system for the determination of biosphere–atmosphere exchange fluxes of PAN using both the hyperbolic relaxed eddy accumulation (HREA) method and the modified Bowen ratio (MBR) method. The system consists of a modified, commercially available gas chromatograph with electron capture detection (GC-ECD, Meteorologie Consult GmbH, Germany). Sampling was performed by trapping PAN onto two pre-concentration columns; during HREA operation one was used for updraft and one for downdraft events, and during MBR operation the two columns allowed simultaneous sampling at two measurement heights. The performance of the PAN flux measurement system was tested at a natural grassland site, using fast-response ozone (O3) measurements as a proxy for both methods. The measured PAN fluxes were comparatively small (daytime PAN deposition was on average −0.07 nmol m−2 s−1) and, thus, prone to significant uncertainties. A major challenge in the design of the system was the resolution of the small PAN mixing ratio differences. Consequently, the study focuses on the performance of the analytical unit and a detailed analysis of errors contributing to the overall uncertainty. The error of the PAN mixing ratio differences ranged from 4 to 15 ppt during the MBR and between 18 and 26 ppt during the HREA operation, while during daytime measured PAN mixing ratios were of similar magnitude. Choosing optimal settings for both the MBR and HREA method, the study shows that the HREA method did not have a significant advantage towards the MBR method under well-mixed conditions as was expected.
Highlights
Peroxyacetyl nitrate (PAN, CH3C(O)O2NO2) is an important organic nitrogen compound, whose production is often associated with the anthropogenic emissions of NOx (= nitrogen monoxide (NO) + NO2) and non-methane hydrocarbons (NMHC) (Stephens, 1969)
We find that hyperbolic relaxed eddy accumulation (HREA) and modified Bowen ratio (MBR) are generally applicable to determine PAN fluxes using our gas chromatograph with electron capture detection (GC-ECD) setup, but the limitation of the analytical unit to precisely resolve mixing ratio differences remains a major drawback
To evaluate the conditions under which the HREA method may be favoured over the MBR method for the presented PAN flux measurements, we examine the ratio of the derived mixing ratio differences by the MBR and HREA method
Summary
Peroxyacetyl nitrate (PAN, CH3C(O)O2NO2) is an important organic nitrogen compound, whose production is often associated with the anthropogenic emissions of NOx (= NO + NO2) and non-methane hydrocarbons (NMHC) (Stephens, 1969). It is formed through the oxidation of the peroxyacetyl radical (PA) with nitrogen dioxide (NO2): CH3C(O)O2 + NO2 + M CH3C(O)O2NO2 + M. A. Moravek et al.: Development of a flux measurement system for PAN. The dry deposition of PAN is a source of nitrogen for remote, nutrient-poor ecosystems and, influences carbon sequestration (Magnani et al, 2007)
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