Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions : (RECONCILE) ; activities and results

The international research project RECONCILE has addressed central questions regarding polar ozone depletion, with the objective to quantify some of the most relevant yet still uncertain physical and chemical processes and thereby improve prognostic modelling capabilities to realistically predict the response of the ozone layer to climate change. This overview paper outlines the scope and the general approach of RECONCILE, and it provides a summary of observations and modelling in 2010 and 2011 that have generated an in many respects unprecedented dataset to study processes in the Arctic winter stratosphere. Principally, it summarises important outcomes of RECONCILE including (i) better constraints and enhanced consistency on the set of parameters governing catalytic ozone destruction cycles, (ii) a better understanding of the role of cold binary aerosols in heterogeneous chlorine activation, (iii) an improved scheme of polar stratospheric cloud (PSC) processes that includes heterogeneous nucleation of nitric acid trihydrate (NAT) and ice on non-volatile background aerosol leading to better model parameterisations with respect to denitrification, and (iv) long transient simulations with a chemistry-climate model (CCM) updated based on the results of RECONCILE that better reproduce past ozone trends in Antarctica and are deemed to produce more reliable predictions of future ozone trends. The process studies and the global simulations conducted in RECONCILE show that in the Arctic, ozone depletion uncertainties in the chemical and microphysical processes are now clearly smaller than the sensitivity to dynamic variability

Aircraft emission mitigation by changing route altitude: A multi-model estimate of aircraft NOx emission impact on O3 photochemistry

The atmospheric impact of aircraft NOx emissions are studied using updated aircraft inventories for the year 2006, in order to estimate the photochemistry-related mitigation potential of shifting cruise altitudes higher or lower by 2000 ft. Applying three chemistry-transport models (CTM) and two climatechemistry models (CCM) in CTM mode, all including detailed tropospheric and stratospheric chemistry, we estimate the short-lived radiative forcing (RF) from O3 to range between 16.4 and 23.5 mW m 2, with a mean value of 19.5 mW m 2. Including the long-lived RF caused by changes in CH4, the total NOxrelated RF is estimated to about 5 mW m 2, ranging 1e8 mW m 2. Cruising at 2000 ft higher altitude increases the total RF due to aircraft NOx emissions by 2 ± 1 mW m 2, while cruising at 2000 ft lower altitude reduces RF by 2 ± 1 mWm 2. This change is mainly controlled by short-lived O3 and show that chemical NOx impact of contrail avoiding measures is likely small

Anthropogenic influence on SOA and the resulting radiative forcing

The effect of chemical changes in the atmosphere since the pre-industrial period on the distributions and burdens of Secondary Organic Aerosol (SOA) has been calculated using the off-line aerosol chemistry transport model Oslo CTM2. The production of SOA was found to have increased from about 35 Tg yr−1 to 53 Tg yr−1 since pre-industrial times, leading to an increase in the global annual mean SOA burden from 0.33 Tg to 0.50 Tg, or about 51%. The effect of allowing semi-volatile species to partition to sulphate aerosol was also tested, leading to an increase in SOA production from about 43 Tg yr−1 to 69 Tg yr−1 since pre-industrial times, while the annual mean SOA burden increased from 0.44 Tg to 0.70 Tg, or about 59%. The increases were greatest over industrialised areas, especially when partitioning to sulphate aerosol was allowed, as well as over regions with high biogenic precursor emissions. The contribution of emissions from different sources to the larger SOA burdens has been calculated. The results suggest that the majority of the increase was caused by emissions of primary organic aerosols (POA), from fossil fuel and bio fuel combustion. As yet, very few radiative forcing estimates of SOA exist, and no such estimates were provided in the latest IPCC report. In this study, we found that the change in SOA burden caused a radiative forcing (defined here as the difference between the pre-industrial and the present day run) of −0.09 W m−2, when SOA was allowed to partition to both organic and sulphate aerosols, and −0.06 W m−2 when only partitioning to organic aerosols was assumed. Therefore, the radiative forcing of SOA was found to be stronger than the best estimate for POA in the latest IPCC assessment.ISSN:1680-7375ISSN:1680-736

Transport impacts on atmosphere and climate: shipping

Emissions of exhaust gases and particles from oceangoing ships are a significant and growing contributor to the total emissions from the transportation sector. We present an assessment of the contribution of gaseous and particulate emissions from oceangoing shipping to anthropogenic emissions and air quality. We also assess the degradation in human health and climate change created by these emissions. Regulating ship emissions requires comprehensive knowledge of current fuel consumption and emissions, understanding of their impact on atmospheric composition and climate, and projections of potential future evolutions and mitigation options. Nearly 70% of ship emissions occur within 400 km of coastlines, causing air quality problems through the formation of ground-level ozone, sulphur emissions and particulate matter in coastal areas and harbours with heavy traffic. Furthermore, ozone and aerosol precursor emissions as well as their derivative species from ships may be transported in the atmosphere over several hundreds of kilometres, and thus contribute to air quality problems further inland, even though they are emitted at sea. In addition, ship emissions impact climate. Recent studies indicate that the cooling due to altered clouds far outweighs the warming effects from greenhouse gases such as carbon dioxide (CO2) or ozone from shipping, overall causing a negative present-day radiative forcing (RF). Current efforts to reduce sulphur and other pollutants from shipping may modify this. However, given the short residence time of sulphate compared to CO2, the climate response from sulphate is of the order decades while that of CO2 is centuries. The climatic trade-off between positive and negative radiative forcing is still a topic of scientific research, but from what is currently known, a simple cancellation of global mean forcing components is potentially inappropriate and a more comprehensive assessment metric is required. The CO2 equivalent emissions using the global temperature change potential (GTP) metric indicate that after 50 years the net global mean effect of current emissions is close to zero through cancellation of warming by CO2 and cooling by sulphate and nitrogen oxides

Atmospheric Composition Change

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