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Observation-based and modeling studies have identified the Eastern Mediterranean and Middle East (EMME) region as a prominent climate change hotspot. While several initiatives have addressed the impacts of climate change in parts of the EMME, here we present an updated assessment, covering a wide range of timescales, phenomena and future pathways. Our assessment is based on a revised analysis of recent observations and projections and an extensive overview of the recent scientific literature on the causes and effects of regional climate change. Greenhouse gas emissions in the EMME are growing rapidly, surpassing those of the European Union, hence contributing significantly to climate change. Over the past half-century and especially during recent decades, the EMME has warmed significantly faster than other inhabited regions. At the same time, changes in the hydrological cycle have become evident. The observed recent temperature increase of about 0.45 degrees C per decade is projected to continue, although strong global greenhouse gas emission reductions could moderate this trend. In addition to projected changes in mean climate conditions, we call attention to extreme weather events with potentially disruptive societal impacts. These include the strongly increasing severity and duration of heatwaves, droughts and dust storms, as well as torrential rain events that can trigger flash floods. Our review is complemented by a discussion of atmospheric pollution and land-use change in the region, including urbanization, desertification and forest fires. Finally, we identify sectors that may be critically affected and formulate adaptation and research recommendations toward greater resilience of the EMME region to climate change.

Mineral dust is an important natural source of aerosols and significantly influences air quality (Querol et al., Environ. Int., 2019) and the global radiation budget (Schepanski, Geosci., 2018). Frequent dust intrusions are observed in the Mediterranean region (Ealo et al., Atmos. Chem. Phys., 2016; Pikridas et al., Atmos. Environ., 2018) and Central Europe (Collaud Coen et al., Atmos. Chem. Phys., 2004; Schauer et al., Aerosol Air Qual. Res., 2016), with high potential to cause exceedances of daily PM10 levels. To separate the influence of anthropogenic and natural contribution to the PM10 levels, the new method was developed within the DNAAP project (Detection of non-anthropogenic air pollution – http://www.aerosol.si/dnaap/). Dust weakly absorbs light in the near ultra-violet and short wavelengths of the visible range, while the light absorption of dust in longer wavelengths from the visible and near infra-red range is negligible. We used filter-based photometer Aethalometer AE33 (Drinovec et al., Atmos. Meas. Tech., 2015) to measure the light absorption at seven wavelengths, from 370 to 950 nm. The mineral dust is not the only light-absorbing aerosol in the air. Black carbon (BC), a unique primary tracer for combustion emissions, strongly absorbs light across the entire visual, near infra-red and near ultra-violet spectral range. Since optical absorption of mineral dust is weaker than the optical absorption of black carbon, the coarse mode mineral particles have to be concentrated using the high-volume virtual impactor (VI). The method is based on the optical absorption measurements of the two sample streams, sampling particle size below 1 µm and sample stream with the concentrated coarse mode particles, where mineral dust contribution is substantial. Experimental configuration includes two Aethalometers AE33 with different size selective inlets: VI inlet for sampling coarse aerosol mode (mostly mineral dust) and PM1 inlet for sampling fine mode of aerosols (mainly BC). The optical absorption of mineral dust can be determined by subtracting the absorption of fine aerosol fraction (PM1) from the absorption of aerosol sampled by the VI, taking into account the enhancement factor of VI setup (Drinovec et al., Atmos. Meas. Tech., 2020). The mineral dust mass concentration is then calculated using mass absorption cross-section (MAC) for dust which could be site and source-region specific. The results from the measurement campaigns performed at six locations in the Mediterranean region will be presented. The measurements took place in NE Spain (Barcelona – BCN, Montseny – MSY, Montsec – MSA), on Cyprus (Nicosia – NI, Agia Marina Xyliatou – AMX), and in Slovenia (Ljubljana – LJ). Two year-long datasets will be presented, focusing on the analyses of aerosol optical properties of PM1 and VI fractions. The results were validated using low time resolution chemical specification of offline filters and a statistical approach where dust was extracted from PM10 measurements for dust intrusions periods determined by models and back-trajectory studies. For better understanding, helium ion microscopy (HIM) was applied to study the microscopic differences between mineral dust and black carbon captured on the AE33 filter tapes. This work was supported by SPIRIT Slovenia – Public Agency for Entrepreneurship, Internationalization, Foreign Investments and Technology, project DNAAP.

International audience

International audience

The role of aerosolized SARS-CoV-2 viruses in airborne transmission of COVID-19 is debated. The transmitting aerosol particles are generated through the breathing and vocalization by infectious subjects. Some authors state that this represents the dominant route of spreading, while others dismiss the option. Public health organizations generally categorize it as a secondary transmission pathway. Here we present a simple, easy-to-use spreadsheet model to estimate the infection risk for different indoor environments, constrained by published data on human aerosol emissions, SARS-CoV-2 viral loads, infective dose and other parameters. We evaluate typical indoor settings such as an office, a classroom, a choir practice room and reception/party environments. These are examples, and the reader is invited to use the algorithm for alternative situations and assumptions. Our results suggest that aerosols from highly infective subjects can effectively transmit COVID-19 in indoor environments. This “highly infective” category represents approximately twenty percent of the patients tested positive for SARS-CoV-2. We find that “super infective” subjects, representing the top five to ten percent of positive-tested ones, plus an unknown fraction of less, but still highly infective, high aerosol-emitting subjects, may cause COVID-19 clusters (>10 infections), e.g. in classrooms, during choir singing and at receptions. The highly infective ones also risk causing such events at parties, for example. In general, active room ventilation and the ubiquitous wearing of face masks (i.e. by all subjects) may reduce the individual infection risk by a factor of five to ten, similar to high-volume HEPA air filtering. The most effective mitigation measure studied is the use of high-quality masks, which can drastically reduce the indoor infection risk through aerosols., medRxiv

International audience; No abstract available.

Carbonaceous particulate matter accounts for a large fraction of fine atmospheric aerosol particles and plays a significant role on air quality and climate forcing. Although various primary sources and secondary transformation processes have already been identified and quantified worldwide, its characterization over long term time periods remains poorly documented. We report here the first source apportionment of carbonaceous aerosols for a 5+ year period from in situ on line measurements at a suburban background site (SIRTA) located in the Paris region (France). Submicron non refractory aerosols were measured using an aerosol chemical speciation monitor (ACSM) with a 30 min time resolution, while equivalent mass concentration of BC was measured by a seven wavelength aethalometer with 1 min frequency. The relative source contributions of wood burning and traffic emissions to black carbon were estimated using the ‘aethalometer model’. Positive matrix factorization, based on ME 2 engine, was applied to apportion the organic aerosol (OA) sources using the advanced Source Finder toolkit (SoFi Pro), specifically designed to robustly identify the expected factors even over multi year time scales. Results obtained with SoFi Pro were then compared to the standard SoFi outputs, corresponding to 12 successive ME 2 computations for the 2014 2017 period. Converging results nicely illustrated seasonal, weekly, and diurnal cycles of the various primary and secondary carbonaceous aerosol fractions, and offer a unique immersion into the seasonal characteristics of secondary OA (SOA) in Paris. Primary carbonaceous showed higher concentrations in winter due to enhanced wood burning emissions during the heating season. SOA dominated the total carbonaceous aerosol loading all around the year as a result of regional transport and local physicochemical formation processes. Less and more oxidized SOA fractions have been highlighted for the entire studied period. Finally, the impact of aqueous (heterogeneous) and photochemical processes on the SOA formation was also addressed.