A 3D chemistry transport model study of changes in atmospheric ozone due to aircraft NOx emissions
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Peroxyacetyl nitrate
Atmospheric chemistry
Nitrogen oxides
Chemical Transport Model
Mixing ratio
Tropospheric ozone
Emission inventory
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
Mixing ratio
Tropical Atlantic
Middle latitudes
Tropospheric ozone
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Measurements of important reactive nitrogen species (NO, NO 2 , HNO 3 , PAN, PPN, NO 3 − , NO y ), C 1 to C 6 hydrocarbons, O 3 , chemical tracers (C 2 Cl 4 , CO), and meteorological parameters were made in the troposphere (0 to 12 km) over the western Pacific (0°–50°N) during the Pacific Exploratory Mission‐West A campaign (September–October 1991). Under clean conditions, mixing ratios of NO, NO 2 , NO y , and O 3 increased with altitude and showed a distinct latitudinal gradient. PAN showed a midtropospheric maximum, while nitric acid mixing ratios were generally highest near the surface. Measured NO y concentrations were significantly greater than the sum of individually measured nitrogen species (mainly NO x , PAN, and HNO 3 ), suggesting that a large fraction of reactive nitrogen present in the atmosphere is made up of hitherto unknown species. This shortfall was larger in the tropics (≈65%) compared to midlatitudes (≈40%) and was minimal in air masses with high HNO 3 mixing ratios (>100 ppt). A global three‐dimensional photochemical model has been used to compare observations with predictions and to assess the significance of major sources. It is possible that the tropical lightning source is much greater than commonly assumed, and both lightning source and its distribution remain a major area of uncertainty in the budgets of NO y and NO x . A large disagreement between measurement and theory exists in the atmospheric distribution of HNO 3 . It appears that surface‐based anthropogenic emissions provide nearly 65% of the global atmospheric NO y reservoir. Relatively constant NO x /NO y ratios imply that NO y and NO x are in chemical equilibrium and the NO y reservoir may be an important in situ source of atmospheric NO x . Data are interpreted to suggest that only about 20% of the upper tropospheric (7–12 km) NO x is directly attributable to its surface NO x source, and free tropospheric sources are dominant. In situ release of NO x from the NO y reservoir, lightning, direct transport of surface NO x , aircraft emissions, and small stratospheric input collectively maintain the NO x balance in the atmosphere. It is shown that atmospheric ratios of reactive nitrogen and sulfur species, along with trajectory analysis, can be used to pinpoint the source of Asian continental outflow. Compared to rural atmospheres over North America, air masses over the Pacific are highly efficient in net O 3 production. Sources of tropospheric NO x cannot yet be accurately defined due to shortcomings in measurements and theory.
Reactive nitrogen
Mixing ratio
Chemical Transport Model
Peroxyacetyl nitrate
Middle latitudes
Tropospheric ozone
Atmospheric chemistry
Lightning
Nitrogen dioxide
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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
Mixing ratio
Reactive nitrogen
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Peroxyacetyl nitrate
Mixing ratio
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Peroxyacetyl nitrate
Mixing ratio
Atmospheric instability
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Peroxyacetyl nitrate
Mixing ratio
Reactive nitrogen
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Citations (52)
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
Mixing ratio
Deposition
Trace gas
Reactive nitrogen
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Peroxyacetyl nitrate
Mixing ratio
Nitrogen dioxide
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Peroxyacetyl nitrate
Nitrogen oxides
Nitrogen oxides
Nitrogen dioxide
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