The chemistry of Antarctic ozone 1960-1987

The factors that influence Antarctic ozone are examined with a view to understanding the observed historical trend. Researchers show that reduced ambient temperatures can dramatically enhance the efficiency of chemical removal processes. Attention is focused on positive feedback between levels of ozone, temperature, and rates of heterogeneous chemical reactions. ClO and its dimer, and high levels of these gases are maintained until the clouds evaporate, on 15 September for the simulation shown here

Chemical ozone loss in the Arctic winter 1991–1992

Chemical ozone loss in winter 1991–1992 is recalculated based on observations of the HALOE satellite instrument, Version 19, ER-2 aircraft measurements and balloon data. HALOE satellite observations are shown to be reliable in the lower stratosphere below 400 K, at altitudes where the measurements are most likely disturbed by the enhanced sulfate aerosol loading, as a result of the Mt.~Pinatubo eruption in June 1991. Significant chemical ozone loss (13–17 DU) is observed below 380 K from Kiruna balloon observations and HALOE satellite data between December 1991 and March 1992. For the two winters after the Mt. Pinatubo eruption, HALOE satellite observations show a stronger extent of chemical ozone loss towards lower altitudes compared to other Arctic winters between 1991 and 2003. In spite of already occurring deactivation of chlorine in March 1992, MIPAS-B and LPMA balloon observations indicate that chlorine was still activated at lower altitudes, consistent with observed chemical ozone loss occurring between February and March and April. Large chemical ozone loss of more than 70 DU in the Arctic winter 1991–1992 as calculated in earlier studies is corroborated here

New retrieval of BrO from SCIAMACHY limb: an estimate of the stratospheric bromine loading during April 2008

We present a new retrieval of stratospheric BrO (bromine monoxide) from channel 2 SCIAMACHY (SCanning Imaging Absorption spectrometer for Atmospheric CHartographY) limb observations. Retrievals are shown to agree with independent balloon observations to within one standard deviation of the retrieval noise. We retrieve BrO profiles for all of April 2008, and apply simulated [BrO]/[Br_y] (bromine monoxide : stratospheric inorganic bromine) ratios to estimate the stratospheric Br_y loading. We find 23.5 ± 6 ppt Br, suggesting 7 ppt Br from short-lived bromocarbons to be at the high end of the current best estimate (3–8 ppt). The 6 ppt Br uncertainty estimate is dominated by the 21% uncertainty in the simulated [BrO] / [Br_y] ratio due to propagation of errors from the underlying chemical kinetics

OH, HO_2, NO in two biomass burning plumes: Sources of HO_x and implications for ozone production

The ER-2 made two descents through upper tropospheric biomass burning plumes during ASHOE/MAESA. HO_x (= OH + HO_2) concentrations are largely self-limited outside the plumes, but become progressively more limited by reactions with NO_x (= NO + NO_2) at the higher NO_x concentrations inside the plumes. Sources of HO_x in addition to H_(2)O and CH_4 oxidation are required to balance the known HOx sinks both in the plumes and in the background upper troposphere. HO_x concentrations were consistently underestimated by a model constrained by observed NO_x concentrations. The size of the model underestimate is reduced when acetone photolysis is included. Models which do not include the additional HO_x sources required to balance the HO_x budget are likely to underestimate ozone production rates

The Effect of Representing Bromine from VSLS on the Simulation and Evolution of Antarctic Ozone

We use the Goddard Earth Observing System Chemistry Climate Model (GEOSCCM), a contributor to both the 2010 and 2014 WMO Ozone Assessment Reports, to show that inclusion of 5 parts per trillion (ppt) of stratospheric bromine(Br(sub y)) from very short lived substances (VSLS) is responsible for about a decade delay in ozone hole recovery. These results partially explain the significantly later recovery of Antarctic ozone noted in the 2014 report, as bromine from VSLS was not included in the 2010 Assessment. We show multiple lines of evidence that simulations that account for VSLS Br(sub y) are in better agreement with both total column BrO and the seasonal evolution of Antarctic ozone reported by the Ozone Monitoring Instrument (OMI) on NASAs Aura satellite. In addition, the near zero ozone levels observed in the deep Antarctic lower stratospheric polar vortex are only reproduced in a simulation that includes this Br(sub y) source from VSLS

Ozone Production and Loss Rate Measurements in the Middle Stratosphere

The first simultaneous measurements of HO(x), NO(x), and Cl(x) radicals in the middle stratosphere show that NO(x) catalytic cycles dominate loss of ozone (O3) for altitudes between 24 and 38 km; Cl(x) catalytic cycles are measured to be less effective than previously expected; and there is no 'ozone deficit' in the photochemically dominated altitude range from 31 and 38 km, contrary to some previous theoretical studies

Bromoform and dibromomethane above the Mauritanian upwelling: Atmospheric distributions and oceanic emissions

Natural sources of bromoform (CHBr3) and dibromomethane (CH2Br2), including oceanic emissions, contribute to stratospheric and tropospheric O3 depletion. Convective transport over tropical oceans could deliver large amounts of these short-lived organic bromine species to the upper atmosphere. High mixing ratios of atmospheric CHBr3 in air masses from the northwest African coast have been hypothesized to originate from the biologically active Mauritanian upwelling. During a cruise into the upwelling source region in spring 2005 the atmospheric mixing ratios of the brominated compounds CHBr3 and CH2Br2 were found to be elevated above the marine background and comparable to measurements in other coastal regions. The shelf waters were identified as a source of both compounds for the atmosphere. The calculated sea-to-air emissions support the hypothesis of a strong upwelling source for reactive organic bromine. However, calculated emissions were not sufficient to explain the elevated concentrations observed in the coastal atmosphere. Other strong sources that could contribute to the large atmospheric mixing ratios previously observed over the Atlantic Ocean must exist within or near West Africa

Characterization of soluble bromide measurements and a case study of BrO observations during ARCTAS

A focus of the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission was examination of bromine photochemistry in the spring time high latitude troposphere based on aircraft and satellite measurements of bromine oxide (BrO) and related species. The NASA DC-8 aircraft utilized a chemical ionization mass spectrometer (CIMS) to measure BrO and a mist chamber (MC) to measure soluble bromide. We have determined that the MC detection efficiency to molecular bromine (Br2), hypobromous acid (HOBr), bromine oxide (BrO), and hydrogen bromide (HBr) as soluble bromide (Br−) was 0.9±0.1, 1.06+0.30/−0.35, 0.4±0.1, and 0.95±0.1, respectively. These efficiency factors were used to estimate soluble bromide levels along the DC-8 flight track of 17 April 2008 from photochemical calculations constrained to in situ BrO measured by CIMS. During this flight, the highest levels of soluble bromide and BrO were observed and atmospheric conditions were ideal for the space-borne observation of BrO. The good agreement (R2 = 0.76; slope = 0.95; intercept = −3.4 pmol mol−1) between modeled and observed soluble bromide, when BrO was above detection limit (\u3e2 pmol mol−1) under unpolluted conditions (NOmol−1), indicates that the CIMS BrO measurements were consistent with the MC soluble bromide and that a well characterized MC can be used to derive mixing ratios of some reactive bromine compounds. Tropospheric BrO vertical column densities (BrOVCD) derived from CIMS BrO observations compare well with BrOTROPVCD from OMI on 17 April 2008