Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Periodic Report Summary 1 - REQUA (Regional climate-air quality interactions)

The main objective of REQUA is the strengthening the research partnership through staff exchanges and networking activities between research groups in Europe, the USA and China working on the field of regional climate-air quality interactions and advance the investigation of atmospheric processes determining earth’s climate as well as the current understanding of interactions between different components of the earth system.
The climate and the air quality are intimately interactive parts of the earth's system with their feedbacks being amplified in regional scales for the short-lived gas-phase species and aerosols. These interactions are critical for understanding the behavior of the earth system and should be taken into consideration for the design of future effective environmental policies. REQUA was designed to address these complex regional climate - air quality interactions by applying different modeling-based methodologies including:
a) Evaluation and comparison studies of different state-of-the art coupled regional climate-air quality models to assess model uncertainties and quantify systematic model biases.
b) Process oriented evaluation studies to assess the ability of regional and global models to reproduce adequately specific events with important societal impacts in regional scales such as heat waves, stratospheric intrusions and forest fires.
c) Model developments and sensitivity studies aiming at optimizing model performance and prioritizing the relative importance of selected parameters on physical processes.
d) Investigation of key transport, chemical and radiative processes determining the distribution of pollutants such as ozone and aerosols in coupled atmospheric models.
e) Quantification of the aerosol and tropospheric ozone effects on climate in coupled climate-air quality atmospheric models.
f) Assessment of the impact of past climate variability and future anthropogenic climate change on air pollution levels with emphasis on tropospheric ozone and aerosols.
The outcome of this project will contribute towards the better understanding of the atmospheric environment and the development of regional earth-system models, used by the scientific community for future projections. In this respect, the positive societal impacts of this work are related to the human capacity to interpret sufficiently well atmospheric processes and therefore being in position to project accurately its future evolution.
A series of regional and global climate studies was accomplished within REQUA. Below the most important work performed and the basic scientific findings are summarized.
The role of dust on the radiative balance of the Mediterranean region was investigated using the online regional model RegCM4. The impact of key parameters (number of aerosol size bins, convective scheme etc) on aerosol load was assessed and the optimization of model performance was accomplished by means of sensitivity studies. Evaluation with satellite data indicated that the model underestimates dust optical depth over the gulf of Guinea and overestimates it over eastern Sahara by 60%. The model simulated adequately the dust extinction profile in the first 5 km, although it overestimated it in higher altitudes. The most important climate feedback of dust was caused by scattering/reflecting the incoming solar radiation back to space.
With respect to process oriented evaluation, the RegCM4 regional climate model was employed to quantify a stratospheric intrusion event over the greater Athens area in Greece. The dynamical aspects of the event were analyzed and the model sensitivity to vertical resolution was accessed. The results showed that RegCM4 was able to capture the deep stratospheric intrusion event and its impact on tropospheric ozone levels. The same model was able to reproduce successfully the European heat-wave event of summer 2003, with the model yielding enhanced ozone (O3) production and reduced transmission and diffusion processes, which lead to the increase of ozone.
A number of sensitivity experiments with RegCM4 were performed, aiming to study the regional climate feedback of aerosols over the Mediterranean. Five 10-year simulations were performed including a control, a feedback, an anthropogenic aerosol and two dust runs with different dust parameterizations. The induced changes when including the aerosol feedback were found to be small, in the range of -0.2 to 0.2oC.
Over the Asian domain, the online-coupled regional climate-chemistry model RegCCMS was employed for the study of the interactions between anthropogenic aerosols and the East Asian summer monsoon. In depth-analysis of the impact of aerosol on the climate system indicates that Black Carbon (BC) induces an enhancement of atmospheric circulation, which can increase local floods in south China, while droughts in north China may worsen in response to the BC semi-direct effect. The total aerosol effect was found to be much more significant than the BC direct effect. The East Asian summer monsoon becomes weaker due to the total aerosol effect. However, this weakness could be partially offset by the BC warming effect.
The role of natural and anthropogenic emissions on the radiative balance over China was analyzed with simulations of two regional climate models. Using RegCM4, the anthropogenic secondary organic aerosol direct short wave RF at the surface and at the top of atmosphere was found to be 1.21 and 0.66 W/m2 respectively. RegCCMS was further developed and applied for the study of the sea salt aerosol (SSA) concentrations. The high value center of SSA concentration appears in the South China Sea in winter and in the Yellow Sea in summer. The annual direct radiative forcing at the top of atmosphere of SSA in this area was estimated to be -2.35 W.m-2 and 1.17 W.m-2 for clear sky and all sky, respectively.
The impact of future climate change on atmospheric composition over Europe was studied with two simulations performed under two Representative Concentration Pathway scenarios (RCP4.5 and 8.5). Despite warmer conditions in the future, summer ozone was found to be decreasing, mainly as a result of reduction of emission precursors in the future. A relative enhancement of daily max O3 was seen during autumn.
Global models were employed for the study of the large-scale interactions of climate and atmospheric composition. More specifically, the global composition climate NASA GISS modelE was used to investigate the impact of biomass burning emissions on several key atmospheric species (carbon monoxide (CO), ozone, hydroxyl radicals (OH), and aerosols). Sensitivity studies showed that for free tropospheric O3, biomass burning is not the dominant cause of variability.
A model intercomparison study showed that over the United States two global models (HadGEM3-GA4 and GISS ModelE2) have positive bias in sulfates, with GISS-E2 performing relatively better with a mean bias of +10% and HadGEM3-GA4 with +45%. Comparisons over China indicated that HadGEM3-GA4 model has the best skill in capturing total Aerosol Optical Depth (AOD), and specifically sulfur aerosols in the region. The models differed by up to a factor of six in the simulated change in aerosol optical depth (AOD) and shortwave radiative flux over China. This was due to the reduced sulfate aerosol. Discrepancies were attributed in the response to a combination of substantial differences in the chemical conversion of SO2 to sulfate, translation of sulfate mass into AOD, and model differences in the radiative forcing efficiency of sulfate aerosol.

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