Summertime photochemistry of the troposphere at high northern latitudes

Abstract

The budgets of O3, NOx (NO+NO2), reactive nitrogen (NOy), and acetic acid in the 0–6 km column over western Alaska in summer are examined by photochemical modeling of aircraft and ground‐based measurements from the Arctic Boundary Layer Expedition (ABLE 3A). It is found that concentrations of O3 in the region are regulated mainly by input from the stratosphere, and losses of comparable magnitude from photochemistry and deposition. The concentrations of NOx (10–50 ppt) are sufficiently high to slow down O3 photochemical loss appreciably relative to a NOx‐free atmosphere; if no NOx were present, the lifetime of O3 in the 0–6 km column would decrease from 46 to 26 days because of faster photochemical loss. The small amounts of NOx present in the Arctic troposphere have thus a major impact on the regional O3 budget. Decomposition of peroxyacetyl nitrate (PAN) can account for most of the NOx below 4‐km altitude, but for only 20% at 6‐km altitude. Decomposition of other organic nitrates might supply the missing source of NOx. The lifetime of NOy, in the ABLE 3A flight region is estimated at 29 days, implying that organic nitrate precursors of NOx could be supplied from distant sources including fossil fuel combustion at northern mid‐latitudes. Biomass fire plumes sampled during ABLE 3A were only marginally enriched in O3; this observation is attributed in part to low NOx emissions in the fires, and in part to rapid conversion of NOx to PAN promoted by low atmospheric temperatures. It appears that fires make little contribution to the regional O3 budget. Only 30% of the acetic acid concentrations measured during ABLE 3A can be accounted for by reactions of CH3CO3 with HO2 and CH3O2. There remains a major unidentified source of acetic acid in the atmosphere.

Nitrogen oxides and PAN in plumes from boreal fires during ARCTAS-B and their impact on ozone: an integrated analysis of aircraft and satellite observations

“…Figure 4 shows that the PAN/NO y ratio increases with age in both passes, while the NO x /NO y ratio decreases. These observations of rapid PAN formation confirm the model result of Jacob et al (1992), which showed PAN/NO y in a boreal smoke plume increasing to about 30% in 3 hours. However, the model of Alvarado and Prinn (2009), which simulated the Alaskan fire plume sampled by Goode et al (2000), showed a PAN/NO y ratio of only 4% after 3 h. The key difference between the cases appears to be the emission ratio of NO x in the smoke plumes, which has a large effect on the modeled fractionation of NO y in the smoke plumes.…”

Peroxyacetyl nitrate (PAN) concentrations in the Antarctic troposphere measured during the photochemical experiment at Neumayer (PEAN'99)

“…However, global modelling studies (e.g. Wang et al, 1998) show that surface OH concentrations in higher southern latitudes in January can be lower by a factor of 2}4 compared to northern mid-latitudes where PAN decay rates are comparable to NO V destruction rates (Jacob et al, 1992). Taking into account these uncertainties in the OH mixing ratios during the campaign, the calculation of the NO V destruction of 0.7 pptv h\ is only a rough estimate.…”

“…Further modelling studies have shown that these NO V production rates were su$cient to establish NO V mixing ratios of less than 10 pptv. Observations made in the middle to lower summertime troposphere over Alaska have indicated that under certain conditions the thermal decomposition of PAN alone could account for the concurrent measured NO V abundance in the lower 6-km tropospheric column (Singh et al, 1992b), whereas in other cases the middle tropospheric (4}6 km) abundance of NO V may have been controlled by the degradation of other organic nitrates due to photolysis or reaction with OH (Jacob et al, 1992).…”

“…Jacob et al (1992) demonstrated that the main chemical sink is the reaction of NO with OH forming nitric acid HNO . For this reaction they found averaged rates of 2 pptv h\ in the lower 1 km of the troposphere over the North American continent.…”

Emission Ratios for Ammonia and Formic Acid and Observations of Peroxy Acetyl Nitrate (PAN) and Ethylene in Biomass Burning Smoke as Seen by the Tropospheric Emission Spectrometer (TES)

“…The primary NO x emissions from biomass burning are rapidly converted to PAN within biomass burning plumes [12,37]. Satellite retrievals of PAN could provide substantial information on the fate of NO x emitted by biomass burning in the atmosphere and the impact of these NO x emissions on global tropospheric ozone.…”