We report on the evolution of tropospheric nitrogen dioxide (NO 2) over Spain, focusing on the densely populated cities of Barcelona, Bilbao, Madrid, Sevilla and Valencia, during 17 years, from 1996 to 2012. This data series combines observations from in-situ air quality monitoring networks and the satellite-based instruments GOME and SCIAMACHY. The results in these five cities show a smooth decrease in the NO 2 concentrations of ∼2% per year in the period 1996-2008, due to the implementation of emissions control environmental legislation, and a more abrupt descend of ∼7% per year from 2008 to 2012 as a consequence of the economic recession. In the whole Spanish territory the NO 2 levels have decreased by ∼22% from 1996 to 2012. Statistical analysis of several economic indicators is used to investigate the different factors driving the NO 2 concentration trends over Spain during the last two decades. ; Peer Reviewed
18 pags., 10 figs., 2 tabs. ; Recent observations have shown the ubiquitous presence of iodine oxide (IO) in the Indian Ocean marine boundary layer (MBL). In this study, we use the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem version 3.7.1), including halogen (Br, Cl, and I) sources and chemistry, to quantify the impacts of the observed levels of iodine on the chemical composition of the MBL. The model results show that emissions of inorganic iodine species resulting from the deposition of ozone (span classCombining double low line"inline-formula"O3/span) on the sea surface are needed to reproduce the observed levels of IO, although the current parameterizations overestimate the atmospheric concentrations. After reducing the inorganic emissions by 40 %, a reasonable match with cruise-based observations is found, with the model predicting values between 0.1 and 1.2 span classCombining double low line"inline-formula"pptv/span across the model domain MBL. A strong seasonal variation is also observed, with lower iodine concentrations predicted during the monsoon period, when clean oceanic air advects towards the Indian subcontinent, and higher iodine concentrations predicted during the winter period, when polluted air from the Indian subcontinent increases the ozone concentrations in the remote MBL. The results show that significant changes are caused by the inclusion of iodine chemistry, with iodine-catalysed reactions leading to regional changes of up to 25 % in span classCombining double low line"inline-formula"O3/span, 50 % in nitrogen oxides (NO and span classCombining double low line"inline-formula"NO2/span), 15 % in hydroxyl radicals (OH), 25 % in hydroperoxyl radicals (span classCombining double low line"inline-formula"HO2/span), and up to a 50 % change in the nitrate radical (span classCombining double low line"inline-formula"NO3/span), with lower mean values across the domain. Most of the large relative changes are observed in the open-ocean MBL, although iodine chemistry also affects the chemical composition in the coastal environment and over the Indian subcontinent. These results show the importance of including iodine chemistry in modelling the atmosphere in this region./ ; The IITM is funded by the Ministry of Earth Sciences (MOES), government of India. This study has been funded by the European Research Council Executive Agency under the European Union's Horizon 2020 research and innovation programme (project "ERC-2016-COG 726349 CLIMAHAL").
14 pags., 10 figs. ; Iodine plays a vital role in oxidation chemistry over Antarctica, with past observations showing highly elevated levels of iodine oxide (IO) leading to severe depletion of boundary layer ozone in West Antarctica. Here, we present MAX-DOAS-based (multi-axis differential absorption spectroscopy) observations of IO over three summers (2015-2017) at the Indian Antarctic bases of Bharati and Maitri. IO was observed during all the campaigns with mixing ratios below 2ĝ€¯pptv (parts per trillion by volume) for the three summers, which are lower than the peak levels observed in West Antarctica. This suggests that sources in West Antarctica are different or stronger than sources of iodine compounds in East Antarctica, the nature of which is still uncertain. Vertical profiles estimated using a profile retrieval algorithm showed decreasing gradients with a peak in the lower boundary layer. The ground-based instrument retrieved vertical column densities (VCDs) were approximately a factor of 3 to 5 higher than the VCDs reported using satellite-based instruments, which is most likely related to the sensitivities of the measurement techniques. Air mass back-trajectory analysis failed to highlight a source region, with most of the air masses coming from coastal or continental regions. This study highlights the variation in iodine chemistry in different regions in Antarctica and the importance of a long-term dataset to validate models estimating the impacts of iodine chemistry. ; The ISEA campaigns are organized by the National Centre for Polar and Ocean Research (NCPOR), Ministry of Earth Sciences (MOES), Government of India.IITM and NCPOR are funded by MOES, Government of India.
20 pags., 9 figs., 1 tab. ; Biogenic very short-lived bromocarbons (VSLBr) currently represent 25% of the total stratospheric bromine loading. Owing to their much shorter lifetime compared to anthropogenic long-lived bromine (e.g. halons) and chlorine (e.g. chlorofluorocarbons), the impact of VSLBr on ozone peaks in the lowermost stratosphere, which is a key climatic and radiative atmospheric region. Here we present a modelling study of the evolution of stratospheric ozone and its chemical loss within the tropics and at mid-latitudes during the 21st century. Two different experiments are explored: considering and neglecting the additional stratospheric injection of 5 ppt biogenic bromine naturally released from the ocean. Our analysis shows that the inclusion of VSLBr results in a realistic stratospheric bromine loading and improves the agreement between the model and satellite observations of the total ozone column (TOC) for the 1980 2015 period at mid-latitudes. We show that the overall ozone response to VSLBr at mid-latitudes follows the stratospheric evolution of long-lived inorganic chlorine and bromine throughout the 21st century. Additional ozone loss due to VSLBr is maximized during the present-day period (1990 2010), with TOC differences of 8DU (3 %) and 5:5DU (2 %) for the Southern Hemisphere and Northern Hemisphere midlatitudes (SH-MLs and NH-MLs), respectively. Moreover, the projected TOC differences at the end of the 21st century are 50% lower than the values found for the present-day period. We find that seasonal VSLBr impact on lowermost stratospheric ozone at mid-latitude is influenced by the seasonality of the heterogeneous inorganic-chlorine reactivation processes on ice crystals. Indeed, due to the more efficient reactivation of chlorine reservoirs (mainly ClONO2 and HCl) within the colder SH-ML lowermost stratosphere, the seasonal VSLBr impact shows a small but persistent hemispheric asymmetry through the whole modelled period. Our results indicate that, although the overall VSLBr-driven ozone destruction is greatest during spring, the halogen-mediated (Halogx-Loss) ozone loss cycle in the mid-latitude lowermost stratosphere during winter is comparatively more efficient than the HOx cycle with respect to other seasons. Indeed, when VSLBr are considered, Halogx-Loss dominates wintertime lowermost stratospheric ozone loss at SH-MLs between 1985 and 2020, with a contribution of inter-halogen ClOx BrOx cycles to Halogx-Loss of 50 %. Within the tropics, a small (2:5 DU) and relatively constant (1 %) ozone depletion mediated by VSLBr is closely related to their fixed emissions throughout the modelled period. By including the VSLBr sources, the seasonal Halogx-Loss contribution to lowermost stratospheric ozone loss is practically dominated by the BrOx cycle, reflecting the low sensitivity of very short-lived (VSL) bromine to background halogen abundances to drive tropical stratospheric ozone depletion. We conclude that the link between biogenic bromine sources and seasonal changes in heterogeneous chlorine reactivation is a key feature for future projections of mid-latitude lowermost stratospheric ozone during the 21st century. ; This research has been supported by the European Research Council Executive Agency under the European Union's Horizon 2020 Research and Innovation programme (grant no. ERC-2016-COG 726349 CLIMAHAL) and the Agencia Nacional de Promoción Científica y Técnica (grant no. ANPCYT PICT-2016-0714).
17 pags, 11 figs, 4 tabs ; We demonstrate a new instrument for in situ detection of atmospheric iodine atoms and molecules based on atomic and molecular resonance and off-resonance ultraviolet fluorescence excited by lamp emission. The instrument combines the robustness, light weight, low power consumption and efficient excitation of radio-frequency discharge light sources with the high sensitivity of the photon counting technique. Calibration of I-2 fluorescence is achieved via quantitative detection of the molecule by Incoherent Broad Band Cavity-enhanced Absorption Spectroscopy. Atomic iodine fluorescence signal is calibrated by controlled broad band photolysis of known I-2 concentrations in the visible spectral range at atmospheric pressure. The instrument has been optimised in laboratory experiments to reach detection limits of 1.2 pptv for I atoms and 13 pptv for I-2, for S/N = 1 and 10 min of integration time. The ROFLEX system has been deployed in a field campaign in northern Spain, representing the first concurrent observation of ambient mixing ratios of iodine atoms and molecules in the 1-350 pptv range. ; The authors are grateful to C. S. E. Bale, P. Spietz, M. D. Andres Hernandez, F. Keutsch, E. Boyle, S. Vaughan, J. Orphal and J. M. C. Plane for support and helpful comments. This work was funded by the Spanish Research Council (CSIC) and the Regional Government of Castilla-La Mancha (FGMACLM). ; Peer reviewed
Halogen ( Cl , Br, and I) chemistry has been reported to influence the formation of secondary air pollutants. Previous studies mostly focused on the impact of chlorine species on air quality over large spatial scales. Very little attention has been paid to the effect of the combined halogen chemistry on air quality over Europe and its implications for control policy. In the present study, we apply a widely used regional model, the Community Multiscale Air Quality Modeling System (CMAQ), incorporated with the latest halogen sources and chemistry, to simulate the abundance of halogen species over Europe and to examine the role of halogens in the formation of secondary air pollution. The results suggest that the CMAQ model is able to reproduce the level of O 3 , NO 2 , and halogen species over Europe. Chlorine chemistry slightly increases the levels of OH , HO 2 , NO 3 , O 3 , and NO 2 and substantially enhances the level of the Cl radical. Combined halogen chemistry induces complex effects on OH (ranging from −0.023 to 0.030 pptv) and HO 2 (in the range of −3.7 to 0.73 pptv), significantly reduces the concentrations of NO 3 (as much as 20 pptv) and O 3 (as much as 10 ppbv), and decreases NO 2 in highly polluted regions (as much as 1.7 ppbv); it increases NO 2 (up to 0.20 ppbv) in other areas. The maximum effects of halogen chemistry occur over oceanic and coastal regions, but some noticeable impacts also occur over continental Europe. Halogen chemistry affects the number of days exceeding the European Union target threshold for the protection of human beings and vegetation from ambient O 3 . In light of the significant impact of halogen chemistry on air quality, we recommend that halogen chemistry be considered for inclusion in air quality policy assessments, particularly in coastal cities.
13 pages, 5 figures, supporting information http://dx.doi.org/10.1002/2014JD022687 ; One of the critical parameters in assessing the global impacts of dimethyl sulfide (DMS) on cloud properties and the radiation budget is the estimation of phytoplankton-induced ocean emissions, which are derived from prescribed, climatological surface seawater DMS concentrations. The most widely used global ocean DMS climatology was published 15 years ago and has recently been updated using a much larger database of observations. The updated climatology displays significant differences in terms of the global distribution and regional monthly averages of sea surface DMS. In this study, we use the ECHAM5-HAMMOZ aerosol-chemistry-climate general circulation model to quantify the influence of the updated DMS climatology in computed atmospheric properties, namely, the spatial and temporal distributions of atmospheric DMS concentration, sulfuric acid concentration, sulfate aerosols, number of activated aerosols, cloud droplet number concentration, and the aerosol radiative forcing at the top of the atmosphere. Significant differences are observed for all the modeled variables. Comparison with observations of atmospheric DMS and total sulfate also shows that in places with large DMS emissions, the updated climatology shows a better match with the observations. This highlights the importance of using the updated climatology for projecting future impacts of oceanic DMS emissions, especially considering that the relative importance of the natural sulfur fluxes is likely to increase due to legislation to "clean up" anthropogenic emissions. The largest estimated differences are in the Southern Ocean, Indian Ocean, and parts of the Pacific Ocean, where the climatologies differ in seasonal concentrations over large geographical areas. The model results also indicate that the former DMS climatology underestimated the effect of DMS on the globally averaged annual aerosol radiative forcing at the top of the atmosphere by about 20% ; The Indian Institute of Tropical Meteorology is supported by the Ministry of Earth Sciences, Government of India. S.-J.R. and R.S. acknowledge support from the former Spanish Ministry of Science and Innovation through projects PRISMA and Malaspina 2010 ; Peer Reviewed
21 pags, 10 figs., 1 tab., 4 apps.-- Open Access funded by Creative Commons Atribution Licence 4.0 ; Although it has been demonstrated that the speed and magnitude of the recent Arctic sea ice decline is unprecedented for the past 1450 years, few records are available to provide a paleoclimate context for Arctic sea ice extent. Bromine enrichment in ice cores has been suggested to indicate the extent of newly formed sea ice areas. Despite the similarities among sea ice indicators and ice core bromine enrichment records, uncertainties still exist regarding the quantitative linkages between bromine reactive chemistry and the first-year sea ice surfaces. Here we present a 120 000-year record of bromine enrichment from the RECAP (REnland ice CAP) ice core, coastal east Greenland, and interpret it as a record of first-year sea ice. We compare it to existing sea ice records from marine cores and tentatively reconstruct past sea ice conditions in the North Atlantic as far north as the Fram Strait (50-85° N). Our interpretation implies that during the last deglaciation, the transition from multi-year to first-year sea ice started at ~17.5 ka, synchronously with sea ice reductions observed in the eastern Nordic Seas and with the increase in North Atlantic ocean temperature. First-year sea ice reached its maximum at 12.4-11.8 ka during the Younger Dryas, after which open-water conditions started to dominate, consistent with sea ice records from the eastern Nordic Seas and the North Icelandic shelf. Our results show that over the last 120 000 years, multi-year sea ice extent was greatest during Marine Isotope Stage (MIS) 2 and possibly during MIS 4, with more extended first-year sea ice during MIS 3 and MIS 5. Sea ice extent during the Holocene (MIS 1) has been less than at any time in the last 120 000 years. ; The RECAP ice coring effort was financed by the Danish Research Council through a Sapere Aude Grant, the NSF through the Division of Polar Programs, the Alfred Wegener Institute, and the European Research Council under the European Community's Seventh Framework Programme (FP7/2007- 2013)/ERC grant agreement 610055 through the Ice2Ice project and the Early Human Impact project (grant agreement 267696). This study has also received funding from the European Research Council Executive Agency under the European Union's Horizon 2020 Research and Innovation programme (Project ERC-2016- COG 726349 CLIMAHAL).
Halogen (Cl, Br, and I) chemistry has been reported to influence the formation of secondary air pollutants. Previous studies mostly focused on the impact of chlorine species on air quality over large spatial scales. Very little attention has been paid to the effect of the combined halogen chemistry on air quality over Europe and its implications for control policy. In the present study, we apply a widely used regional model, the Community Multiscale Air Quality Modeling System (CMAQ), incorporated with the latest halogen sources and chemistry, to simulate the abundance of halogen species over Europe and to examine the role of halogens in the formation of secondary air pollution. The results suggest that the CMAQ model is able to reproduce the level of O3, NO2, and halogen species over Europe. Chlorine chemistry slightly increases the levels of OH, HO2, NO3, O3, and NO2 and substantially enhances the level of the Cl radical. Combined halogen chemistry induces complex effects on OH (ranging from −0.023 to 0.030 pptv) and HO2 (in the range of −3.7 to 0.73 pptv), significantly reduces the concentrations of NO3 (as much as 20 pptv) and O3 (as much as 10 ppbv), and decreases NO2 in highly polluted regions (as much as 1.7 ppbv); it increases NO2 (up to 0.20 ppbv) in other areas. The maximum effects of halogen chemistry occur over oceanic and coastal regions, but some noticeable impacts also occur over continental Europe. Halogen chemistry affects the number of days exceeding the European Union target threshold for the protection of human beings and vegetation from ambient O3. In light of the significant impact of halogen chemistry on air quality, we recommend that halogen chemistry be considered for inclusion in air quality policy assessments, particularly in coastal cities.
Halogen (Cl, Br, and I) chemistry has been reported to influence the formation of secondary air pollutants. Previous studies mostly focused on the impact of chlorine species on air quality over large spatial scales. Very little attention has been paid to the effect of the combined halogen chemistry on air quality over Europe and its implications for control policy. In the present study, we apply a widely used regional model, the Community Multiscale Air Quality Modeling System (CMAQ), incorporated with the latest halogen sources and chemistry, to simulate the abundance of halogen species over Europe and to examine the role of halogens in the formation of secondary air pollution. The results suggest that the CMAQ model is able to reproduce the level of O(3), NO(2), and halogen species over Europe. Chlorine chemistry slightly increases the levels of OH, HO(2), NO(3), O(3), and NO(2) and substantially enhances the level of the Cl radical. Combined halogen chemistry induces complex effects on OH (ranging from –0.023 to 0.030 pptv) and HO(2) (in the range of –3.7 to 0.73 pptv), significantly reduces the concentrations of NO(3) (as much as 20 pptv) and O(3) (as much as 10 ppbv), and decreases NO(2) in highly polluted regions (as much as 1.7 ppbv); it increases NO(2) (up to 0.20 ppbv) in other areas. The maximum effects of halogen chemistry occur over oceanic and coastal regions, but some noticeable impacts also occur over continental Europe. Halogen chemistry affects the number of days exceeding the European Union target threshold for the protection of human beings and vegetation from ambient O(3). In light of the significant impact of halogen chemistry on air quality, we recommend that halogen chemistry be considered for inclusion in air quality policy assessments, particularly in coastal cities.
