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[1] The Antarctic ozone hole demonstrates large-scale, man-made affects on our atmosphere. Surface observations now show that human produced ozone-depleting substances (ODSs) are declining. The ozone hole should soon start to diminish because of this decline. We demonstrate a parametric model of ozone hole area that is based upon a new algorithm for estimating chlorine and bromine levels over Antarctica and late spring Antarctic stratospheric temperatures. This model explains 95% of the ozone hole area's variance. We then use future ODS levels to predict ozone hole recovery. Full recovery to 1980 levels will occur around 2068 and the area will very slowly decline between 2001 and 2017. Detection of a statistically significant decrease of area will not occur until about 2024. We further show that nominal Antarctic stratospheric greenhouse gas forced temperature change should have a small impact on the ozone hole.

Data taken in aircraft transects of emissions plumes from rural U.S. coal-fired power plants were used to confirm and quantify the nonlinear dependence of tropospheric ozone formation on plume NO(x) (NO plus NO(2)) concentration, which is determined by plant NO(x) emission rate and atmospheric dispersion. The ambient availability of reactive volatile organic compounds, principally biogenic isoprene, was also found to modulate ozone production rate and yield in these rural plumes. Differences of a factor of 2 or greater in plume ozone formation rates and yields as a function of NO(x) and volatile organic compound concentrations were consistently observed. These large differences suggest that consideration of power plant NO(x) emission rates and geographic locations in current and future U.S. ozone control strategies could substantially enhance the efficacy of NO(x) reductions from these sources.

Supplemental information Given that air samples stored in metal have been known to sometimes have in-growth of H 2 when stored for significant periods of time, there was concern over the stability of H 2 in the canisters from the Whole Air Sampler. To investigate for this possibility, we analyzed five canister/flask sample pairs that had aliquots separated into evacuated glass flasks 14 to 15 months after initial sampling and ~ 6 months prior to isotopic analysis. Under these

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected.

Abstract.We have integrated observations of tropospheric ozone, very short-lived (VSL) halocarbons and reactive iodine and bromine species from a wide variety of tropical data sources with the global CAM-Chem chemistry-climate model and offline radiative transfer calculations to compute the contribution of halogen chemistry to ozone loss and associated radiative impact in the tropical marine troposphere. The inclusion of tropospheric halogen chemistry in CAM-Chem leads to an annually averaged depletion of around 10 % (∼2.5 Dobson units) of the tropical tropospheric ozone column, with largest effects in the middle to upper troposphere. This depletion contributes approximately −0.10 W m −2 to the radiative flux at the tropical tropopause. This negative flux is of similar magnitude to the ∼0.33 W m −2 contribution of tropospheric ozone to presentday radiative balance as recently estimated from satellite observations. We find that the implementation of oceanic halogen sources and chemistry in climate models is an important component of the natural background ozone budget and we suggest that it needs to be considered when estimating both preindustrial ozone baseline levels and long term changes in tropospheric ozone.

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[1] A ship emission plume experiment was conducted about 100 km off the California coast during the NOAA Intercontinental Transport and Chemical Transformation (ITCT) 2K2 airborne field campaign. Measurements of chemical species were made from the NOAA WP-3D aircraft in eight consecutive transects of a ship plume around midday during 2.5 hours of flight. The measured species include NO x , HNO 3 , peroxyacetylnitrate (PAN), SO 2 , H 2 SO 4 , O 3 , CO, CO 2 , nonmethane hydrocarbons (NMHC), and particle number and size distributions. Observations demonstrate a NO x lifetime of $1.8 hours inside the ship plume compared to $6.5 hours (at noontime) in the moderately polluted background marine boundary layer of the experiment. This confirms the earlier hypothesis of highly enhanced in-plume NO x destruction. Consequently, one would expect the impact of ship emissions is much less severe than those predicted by global models that do not include rapid NO x destruction. Photochemical model calculations suggest that more than 80% of the NO x loss was due to the NO 2 + OH reaction; the remainder was by PAN formation. The model underestimated in-plume NO x loss rate by about 30%. In addition, a comparison of measured to predicted H 2 SO 4 in the plumes suggests that the photochemical model predicts OH variability reasonably well but may underestimate actual values. Predictions of in-plume O 3 production agree well with the observations, suggesting that model-predicted peroxy radical (HO 2 + RO 2 ) levels are reasonable. The model estimated ozone production efficiency ranges from 6 to 30. The largest model bias was seen in the comparison with measured HNO 3 . The model overestimated in-plume HNO 3 by about a factor of 6. This is most likely caused by underestimated HNO 3 sinks possibly involving particle scavenging. However, limited data availability precluded a conclusive test of this possible loss process.