Atmospheric bromoform at Mace Head, Ireland: Evidence for a peatland source

International audienceIn situ atmospheric observations of bromoform (CHBr3) made over a 2.5 year period at Mace Head, Ireland from May 2001?December 2003, including during the NAMBLEX (North Atlantic Marine Boundary Layer Experiment) campaign, show broad maxima from spring until autumn and winter minima, with mixing ratios of 5.3+1.0 pptv (mid March?mid October) and 1.8+0.8 pptv (December?February). This indicates that, unlike CHCl3, which has a summer minimum and winter maximum at Mace Head, local biological sources of CHBr3 have a greater influence on the atmospheric data than photochemical decay during long-range transport. The emission sources are predominantly macroalgal, but we find evidence for a small terrestrial flux from peatland ecosystems, which so far has not been accounted for in the CHBr3 budget. Sharp increases in CHCl3 and CHBr3 concentrations and decreases in O3 concentrations occurred at night when the wind direction switched from an ocean- to a land-based sector (land breeze) and the wind speed dropped to below 5 ms?1. These observations infer a shallow atmospheric boundary layer with increased O3 deposition and concentration of local emissions of both CHCl3 and CHBr3. The ratio of ?CHCl3/?CHBr3 varied strongly according to the prevailing wind direction; from 0.6+0.1 in south-easterly (100?170°) air to 1.9+0.8 in north-easterly (40?70°) air. Of these land-sectors, the south-easterly air masses are likely to be strongly influenced by macroalgal beds along the coast and the emission ratios probably reflect those from seaweeds in addition to land sources. The north-easterly airmasses however have a fetch predominantly over land, which locally is comprised of coastal peatland ecosystems (peat bogs and coastal conifer plantations), previously identified as being strong sources of atmospheric CHCl3 under these conditions. Although we cannot entirely rule out other local land or coastal sources, our observations also suggest peatland ecosystem emissions of CHBr3. We use correlations between CHCl3 and CHBr3 during the land breeze events in conjunction with previous estimates of local wetland CHCl3 release to tentatively deduce a global wetland CHBr3 source of 26.9 (0.5?1247) Gg yr?1, which is approximately 10% of the total global source

Atmospheric bromoform at Mace Head, Ireland: seasonality and evidence for a peatland source

In situ atmospheric observations of bromoform (CHBr₃) made over a 2.5 year period at Mace Head, Ireland from May 2001- Dec 2003, including during the NAMBLEX (North Atlantic Marine Boundary Layer Experiment) campaign, show broad maxima from spring until autumn and winter minima, with mixing ratios of 5.3+1.0 pptv (mid March - mid October) and 1.8+0.8 pptv (December-February). This indicates that, unlike CHCl₃, which has a summer minimum and winter maximum at Mace Head, local biological sources of CHBr₃ have a greater influence on the atmospheric data than photochemical decay during long-range transport. The emission sources are predominantly macroalgal, but we find evidence for a small terrestrial flux from peatland ecosystems, which so far has not been accounted for in the CHBr₃ budget. Sharp increases in CHCl₃ and CHBr₃ concentrations and decreases in O₃ concentrations occurred at night when the wind direction switched from an ocean- to a land-based sector (land breeze) and the wind speed dropped to below 5 ms^-1. These observations infer a shallow atmospheric boundary layer with increased O₃ deposition and concentration of local emissions of both CHCl₃ and CHBr₃. The ratio of ΔCHCl₃/ΔCHBr₃ varied strongly according to the prevailing wind direction; from 0.60+0.15 in south-easterly (100-170° and northerly (340-20°) air to 2.5+0.4 in north-easterly (40-70°) air. Of these land-sectors, the south-easterly air masses are likely to be strongly influenced by macroalgal beds along the coast and the emission ratios probably reflect those from seaweeds in addition to land sources. The north-easterly airmasses however had an immediate fetch inland, which locally is comprised of coastal peatland ecosystems (peat bogs and coastal conifer plantations), previously identified as being strong sources of atmospheric CHCl₃ under these conditions. Although we cannot entirely rule out other local land or coastal sources, our observations also suggest peatland ecosystem emissions of CHBr₃. We use correlations between CHCl₃ and CHBr₃ during the north-easterly land breeze events in conjunction with previous estimates of local wetland CHCl₃ release to tentatively deduce a global wetland CHBr₃ source of 20.4(0.4-948) Gg yr^-1, which is approximately 7% of the total global source

Direct evidence for coastal iodine particles from <i>Laminaria</i> macroalgae ? linkage to emissions of molecular iodine

International audienceRenewal of ultrafine aerosols in the marine boundary layer may lead to repopulation of the marine distribution and ultimately determine the concentration of cloud condensation nuclei (CCN). Thus the formation of nanometre-scale particles can lead to enhanced scattering of incoming radiation and a net cooling of the atmosphere. The recent demonstration of the chamber formation of new particles from the photolytic production of condensable iodine-containing compounds from diiodomethane (CH2I2), (O'Dowd et al., 2002; Kolb, 2002; Jimenez et al., 2003a; Burkholder and Ravishankara, 2003), provides an additional mechanism to the gas-to-particle conversion of sulphuric acid formed in the photo-oxidation of dimethylsulphide for marine aerosol repopulation. CH2I2 is emitted from seaweeds (Carpenter et al., 1999, 2000) and has been suggested as an initiator of particle formation. We demonstrate here for the first time that ultrafine iodine-containing particles are produced by intertidal macroalgae exposed to ambient levels of ozone. The particle composition is very similar both to those formed in the chamber photo-oxidation of diiodomethane and in the oxidation of molecular iodine by ozone. The particles formed in all three systems are similarly aspherical and behave alike when exposed to increased humidity environments. Direct coastal boundary layer observations of molecular iodine, ultrafine particle production and iodocarbons are reported. Using a newly measured molecular iodine photolysis rate, it is shown that, if atomic iodine is involved in the observed particle bursts, it is of the order of at least 1000 times more likely to result from molecular iodine photolysis than diiodomethane photolysis. A hypothesis for molecular iodine release from intertidal macroalgae is presented and the potential importance of macroalgal iodine particles in their contribution to CCN and global radiative forcing are discussed

SAVVY Vaginal Gel (C31G) for Prevention of HIV Infection: A Randomized Controlled Trial in Nigeria

The objective of this trial was to determine the effectiveness of 1.0% C31G (SAVVY) in preventing male-to-female vaginal transmission of HIV infection among women at high risk.This was a Phase 3, double-blind, randomized, placebo-controlled trial. Participants made up to 12 monthly follow-up visits for HIV testing, adverse event reporting, and study product supply. The study was conducted between September 2004 and December 2006 in Lagos and Ibadan, Nigeria, where we enrolled 2153 HIV-negative women at high risk of HIV infection. Participants were randomized 1 ratio 1 to SAVVY or placebo. The effectiveness endpoint was incidence of HIV infection as indicated by detection of HIV antibodies in oral mucosal transudate (rapid test) or blood (ELISA), and confirmed by Western blot or PCR testing. We observed 33 seroconversions (21 in the SAVVY group, 12 in the placebo group). The Kaplan-Meier estimates of the cumulative probability of HIV infection at 12 months were 0.028 in the SAVVY group and 0.015 in the placebo group (2-sided p-value for the log-rank test of treatment effect 0.121). The point estimate of the hazard ratio was 1.7 for SAVVY versus placebo (95% confidence interval 0.9, 3.5). Because of lower-than-expected HIV incidence, we did not observe the required number of HIV infections (66) for adequate power to detect an effect of SAVVY. Follow-up frequencies of adverse events, reproductive tract adverse events, abnormal pelvic examination findings, chlamydial infections and vaginal infections were similar in the study arms. No serious adverse event was attributable to SAVVY use.SAVVY did not reduce the incidence of HIV infection. Although the hazard ratio was higher in the SAVVY than the placebo group, we cannot conclude that there was a harmful treatment effect of SAVVY

Depth profiles of volatile iodine and bromine-containing halocarbons in coastal Antarctic waters

Measurements of bromoform (CHBr3), diiodomethane (CH2I2), chloroiodomethane (CH2ICl) and bromoiodomethane (CH2IBr)were made in the water column (5100 m depth) of the Southern Ocean within 040 km of the Antarctic sea ice during theANTXX1/2 transect of the German R/V Polarstern, at five locations between 7072°S and 911°W in the Antarctic spring/summer of 20032004. Some of the profiles exhibited a very pronounced layer of surface sea-ice meltwater, as evidenced bysalinity minima and temperature maxima, along with surface maxima in concentrations of CHBr3, CH2I2, CH2ICl and CH2IBr.These results are consistent with in situ surface halocarbon production by ice algae liberated from the sea ice, although productionwithin the sea ice followed by transport cannot be entirely ruled out. Additional sub-surface maxima in halocarbons occurredbetween 20 and 80 m. At a station further from shore and not affected by surface sea-ice meltwater, surface concentrations of CH2I2were decreased whereas CH2ICl concentrations were increased compared to the stations influenced by meltwater, consistent withphotochemical conversion of CH2I2 to CH2ICl, perhaps during upward mixing from a layer at &#8764;70 m enhanced in iodocarbons.Mean surface (510 m) water concentrations of halocarbons in these coastal Antarctic waters were 57 pmol l&#8722;1 CHBr3 (range 4478pmol l&#8722;1), 4.2 pmol l&#8722;1 CH2I2 (range 1.78.2 pmol l&#8722;1), 0.8 pmol l&#8722;1 CH2IBr (range 0.21.4 pmol l&#8722;1), and 0.7 pmol l&#8722;1 CH2ICl(range 0.22.4 pmol l&#8722;1). Concurrent measurements in air suggested a sea-air flux of bromoform near the Antarctic coast ofbetween 1 and 100 (mean 32.3, median 10.4) nmol m&#8722;2 day&#8722;1 and saturation anomalies of 5571082% (mean 783%, median733%), similar in magnitude to global shelf values. In surface samples affected by meltwater, CH2I2 fluxes ranged from 0.02 to6.1 nmol m&#8722; 2 day&#8722;1, with mean and median values of 1.9 and 1.1 nmol m&#8722; 2 day&#8722;1, respectively

Atmospheric bromoform at mace head, ireland: seasonality and evidence for a peatland source

In situ atmospheric observations of bromoform (CHBr3) made over a 2.5 year period at Mace Head, Ireland from May 2001- Dec 2003, including during the NAM-BLEX ( North Atlantic Marine Boundary Layer Experiment) campaign, show broad maxima from spring until autumn and winter minima, with mixing ratios of 5.3+1.0 pptv ( mid March - mid October) and 1.8+0.8 pptv ( December-February). This indicates that, unlike CHCl3, which has a summer minimum and winter maximum at Mace Head, local biological sources of CHBr3 have a greater influence on the atmospheric data than photochemical decay during long-range transport. The emission sources are predominantly macroalgal, but we find evidence for a small terrestrial flux from peatland ecosystems, which so far has not been accounted for in the CHBr3 budget. Sharp increases in CHCl3 and CHBr3 concentrations and decreases in O-3 concentrations occurred at night when the wind direction switched from an ocean- to a land-based sector ( land breeze) and the wind speed dropped to below 5 ms(-1). These observations infer a shallow atmospheric boundary layer with increased O3 deposition and concentration of local emissions of both CHCl3 and CHBr3. The ratio of Delta CHCl3/Delta CHBr3 varied strongly according to the prevailing wind direction; from 0.60+ 0.15 in south-easterly ( 100 - 170 degrees) and northerly ( 340 20 degrees) air to 2.5+ 0.4 in north-easterly ( 40 - 70 degrees) air. Of these land-sectors, the south-easterly air masses are likely to be strongly influenced by macroalgal beds along the coast and the emission ratios probably reflect those from seaweeds in addition to land sources. The north-easterly airmasses however had an immediate fetch inland, which locally is comprised of coastal peatland ecosystems ( peat bogs and coastal conifer plantations), previously identified as being strong sources of atmospheric CHCl3 under these conditions. Although we cannot entirely rule out other local land or coastal sources, our observations also suggest peatland ecosystem emissions of CHBr3. We use correlations between CHCl3 and CHBr3 during the north-easterly land breeze events in conjunction with previous estimates of local wetland CHCl3 release to tentatively deduce a global wetland CHBr3 source of 20.4 (0.4 - 948) Gg yr(-1), which is approximately 7% of the total global source