Peroxyacetyl Nitrate (PAN) Measurements During the POPCORN Campaign
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Peroxyacetyl nitrate
Mixing ratio
Aircraft measurements of peroxyacetyl nitrate (PAN) were performed for the first time over the Brazilian Amazon Basin during the wet season (April–May 1987) as part of the NASA Atmospheric Boundary Layer Experiment (ABLE 2B) expedition. In addition to tropical measurements, free tropospheric latitudinal profiles were also obtained during transit flights to and from Manaus, Brazil. Complementing PAN were measurements of NO, O 3 , CO, C 2 Cl 4 , radon, and a variety of other chemical and meteorological parameters. Over the Amazon Basin, PAN was present at a mixing ratio of 5 to 125 ppt. Despite strong local and regional convective activity, a distinct vertical structure with highest mixing ratios aloft was observed. Median PAN mixing ratios of 12, 20, and 48 ppt were present in the 0‐ to 2‐, 2‐ to 4‐, and 4‐ to 6‐km height intervals, respectively. Data collected during the cross‐basin flights showed that the PAN mixing ratio was highest over the rain forest and declined eastward toward the Atlantic Ocean. Over the Atlantic, PAN was low and appeared to be uniformly distributed with height. Above the Amazon forest, PAN was as much as 5 times more abundant than NO x with the largest PAN/NO x ratios occurring at the highest altitudes. Both PAN and possibly the PAN/NO x ratio showed a latitudinal dependence, with decreasing values from the northern midlatitudes to the tropics. Free tropospheric (4–6 km) PAN mixing ratios were found to be strongly correlated with those of O 3 . Preliminary modeling results indicate that a sizeable fraction of NO x and HNO 3 in the free troposphere could result from PAN decomposition alone. The primary source of free tropospheric PAN observed over the Amazon Basin is not well understood. Large‐scale transport from the upper tropospheric PAN reservoir present at the higher northern latitudes, and precursor emissions of nonmethane hydrocarbons from the forest and NO x from soil and lightning clearly play an important role.
Peroxyacetyl nitrate
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Tropical Atlantic
Middle latitudes
Tropospheric ozone
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Aircraft measurements of peroxyacetyl nitrate (PAN) and other important reactive nitrogen species (NO, NO 2 , HNO 3 , and NO y ) were performed over the continental United States and the eastern Pacific during August–September 1986 at all altitudes between O and 6 km as part of CITE 2. PAN measurements were conducted by two independent groups, allowing both intercomparisons and greater confidence in its observed atmospheric structure. PAN was found to be a dominant reactive nitrogen species in the troposphere with 98% of the mixing ratios falling in a range of 5–400 ppt. Typically, the highest mixing ratios (100–300 ppt) were observed aloft (4–6 km) with extremely low values (5–20 ppt) in the marine boundary layer. In the lower troposphere, continental air contained significantly more PAN than marine air. The vertical structure of PAN was largely dictated by its thermal destruction rate and equilibrium with available NO 2 . PAN mixing ratios showed a high degree of variability in both continental and marine atmospheres. Westerly marine air trajectories did not guarantee well‐mixed air of uniform composition. Mixing ratios of O 3 , NO y , NO x , HNO 3 , C 2 H 6 , CO, and CFCl 3 were strongly correlated with those of PAN, indicating the important role played by transport processes. High PAN to NO x ratios in the mid‐troposphere further support the importance of long‐range transport from continental sources. Frequently, descending air masses from the upper troposphere suggested that PAN mixing ratios probably continued to increase above the 6‐km ceiling altitude. Air masses with O 3 <20 ppb, CO <60 ppb, and C 2 H 6 <500 ppt contained only miniscule amounts of PAN and are expected to be of tropical origin. Reasons for the observed PAN variability are discussed.
Peroxyacetyl nitrate
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Reactive nitrogen
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Peroxyacetyl nitrate
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Peroxyacetyl nitrate
Nitrogen oxides
Nitric acid
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Peroxyacetyl nitrate
Peninsula
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Ozone depletion events (ODEs) in the springtime of the Arctic have been frequently observed since the early 1980s, and the correlation between the ozone mixing ratio during the ODEs and the nitrogen oxides (NOx) concentration is still unclear. In the present study, the role of the background level of NOx in ODEs was investigated by using a box model implementing a chemical reaction mechanism containing 49 chemical species and 141 related reactions. A concentration sensitivity analysis was also applied to discover the dependence of the ozone mixing ratio during the ODEs on each constituent of the initial air composition. The simulation results showed that a critical value of the NOx background level exists, with which the ozone depletion rate is independent of the initial concentration of NOx, and the critical value was found to be approximately 55 ppt (ppt = part per trillion, 10−12 mol/mol) in the present study. The concentration sensitivity analysis also showed that the existence of NOx has a two-sided impact on the depletion of ozone, depending on the initial amount of NOx. With a low background level of NOx (less than 55 ppt), the increase of the initial NOx can advance the ozone depletion. On the contrary, with a high initial NOx level (more than 55 ppt), NOx would delay the consumption of ozone during the ODEs.
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Ozone Depletion
Nitrogen oxides
Nitrogen dioxide
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Peroxyacetyl nitrate
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Reactive nitrogen
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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.
Peroxyacetyl nitrate
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Deposition
Trace gas
Reactive nitrogen
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Peroxyacetyl nitrate
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Nitrogen dioxide
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