Submicron aerosol pollution in Greater Cairo (Egypt): A new type of urban haze?

Greater Cairo, the largest megacity of the Middle East North Africa (MENA) region, is currently suffering from major aerosol pollution, posing a significant threat to public health. However, the main sources of pollution remain insufficiently characterized due to limited atmospheric observations. To bridge this knowledge gap, we conducted a continuous 2-month field study during the winter of 2019-2020 at an urban background site, documenting for the first time the chemical and physical properties of submicron (PM1) aerosols. Crustal material from both desert dust and road traffic dust resuspension contributed as much as 24 % of the total PM1 mass (rising to 66 % during desert dust events), a figure not commonly observed in urban environments. Our observations showed significant decreases in black carbon concentrations and ammonium sulfate compared to data from 15 years ago, indicating an important reduction in both local and regional emissions as a result of effective mitigation measures. The diurnal variability of carbonaceous aerosols was attributed to emissions emanating from local traffic at rush hours and nighttime open biomass burning. Surprisingly, semi-volatile ammonium chloride (NH4Cl) originating from local open biomass and waste burning was found to be the main chemical species in PM1 over Cairo. Its nighttime formation contributed to aerosol water uptake during morning hours, thereby playing a major role in the build-up of urban haze. While our results confirm the persistence of a significant dust reservoir over Cairo, they also unveil an additional source of highly hygroscopic (semi-volatile) inorganic salts, leading to a unique type of urban haze. This haze, with dominant contributors present in both submicron (primarily as NH4Cl) and supermicron (largely as dust) modes, underscores the potential implications of heterogeneous chemical transformation of air pollutants in urban environments.

Emission of volatile organic compounds from residential biomass burning and their rapid chemical transformations.

Biomass combustion releases a complex array of Volatile Organic Compounds (VOCs) that pose significant challenges to air quality and human health. Although biomass burning has been extensively studied at ecosystem levels, understanding the atmospheric transformation and impact on air quality of emissions in urban environments remains challenging due to complex sources and burning materials. In this study, we investigate the VOC emission rates and atmospheric chemical processing of predominantly wood burning emissions in a small urban centre in Greece. Ioannina is situated in a valley within the Dinaric Alps and experiences intense atmospheric pollution accumulation during winter due to its topography and high wood burning activity. During pollution event days, the ambient mixing ratios of key VOC species were found to be similar to those reported for major urban centres worldwide. Positive matrix factorisation (PMF) analysis revealed that biomass burning was the dominant emission source (>50 %), representing two thirds of OH reactivity, which indicates a highly reactive atmospheric mixture. Calculated OH reactivity ranges from 5 s-1 to an unprecedented 278 s-1, and averages at 93 ± 66 s-1 at 9 PM, indicating the presence of exceptionally reactive VOCs. The highly pronounced photochemical formation of organic acids coincided with the formation of ozone, highlighting the significance of secondary formation of pollutants in poorly ventilated urban areas. Our findings underscore the pressing need to transition from wood burning to environmentally friendly sources of energy in poorly ventilated urban areas, in order to improve air quality and safeguard public health.

Comprehensive chemical characterization of PM2.5 in the large East Mediterranean-Middle East city of Beirut, Lebanon.

The chemical composition of PM2.5 at two sites in Lebanon, a country in the East Mediterranean - Middle East region, is investigated in the spring and summer seasons. The average PM2.5 concentrations were of (29 ± 16) µg/m3 for Beirut urban site and (32 ± 14) µg/m3 for Beirut suburban site. This study showed that the geographic location of the East Mediterranean region, such as its proximity to the Mediterranean Sea and the dust storm intrusion are a significant contributor to the high PM levels from natural sources, which cannot be mitigated, rendering the PM2.5 WHO annual Air Quality guideline unattainable due to high natural background, which also applies to the entire Middle East region. Turkey and Eastern Europe are the dominant origin of air masses throughout our sampling days, suggesting the long-range transport as an important potential contributor to the high observed concentrations of V, Ni, and sulfate in this region most probably in other East Mediterranean countries than Lebanon too. Main local sources determined through the chemical speciation including organics are road transport, resuspension of dust and diesel private generators. A health risk assessment of airborne metals was performed and the carcinogenic risk for all the metals exceeded by 42 (adults) and 14 (children) times the acceptable risk level (10-6) at both sites. Vanadium was the predominant carcinogenic metal, emphasizing the need to replace energy production with cleaner energy on a regional level and highlighting the severe impact of air pollution on the health of inhabitants in this region's main cities.

Reconciling a national methane emission inventory with in-situ measurements.

Reconciling top-down and bottom-up country-level greenhouse gas emission estimates remains a key challenge in the MRV (Monitoring, Reporting, Verification) paradigm. Here we propose to independently quantify cumulative emissions from a significant number of methane (CH4) emitters at national level and derive robust constraints for the national inventory. Methane emissions in Cyprus, an insular country, stem primarily from waste and agricultural activities. We performed 24 intensive survey days of mobile measurements of CH4 from October 2020 to September 2021 at emission 'hotspots' in Cyprus accounting together for about 28 % of national CH4 emissions. The surveyed areas include a large active landfill (Koshi, 8 % of total emissions), a large closed landfill (Kotsiatis, 18 %), and a concentrated cattle farm area (Aradippou, 2 %). Emission rates for each site were estimated using repeated downwind transects and a Gaussian plume dispersion model. The calculated methane emissions from landfills of Koshi and Kotsiatis (25.9 ± 6.4 Gg yr-1) and enteric fermentation of cattle (10.4 ± 4.4 Gg yr-1) were about 129 % and 40 % larger, respectively than the bottom-up sectorial annual estimates used in the national UNFCCC inventory. The parametrization of the Gaussian plume model dominates the uncertainty in our method, with a typical 21 % uncertainty. Seasonal variations have little influence on the results. We show that using an ensemble of in situ measurements targeting representative methane emission hotspots with consistent temporal and spatial coverage can contribute to the monitoring and validation of national bottom-up emission inventories.

Fine aerosol sources at an urban background site in the Eastern Mediterranean (Nicosia; Cyprus): Insights from offline versus online source apportionment comparison for carbonaceous aerosols.

A total of 348 daily PM2.5 samples were collected at an urban background site of Nicosia, capital of Cyprus, for one-year period (October 2018-October 2019) to assess the origin and sources of fine PM at the Eastern Mediterranean, a poorly characterized area of the world. The samples were analysed for water soluble ionic species, elemental and organic carbon, carbohydrates and trace metals, the combination of which were utilized to identify pollution sources by applying Positive Matrix Factorization (PMF). Six PM2.5 sources, namely long-range transport (LRT; 38 %), traffic (20 %), biomass burning (16 %), dust (10 %), sea salt (9 %) and heavy oil combustion (7 %), were identified. Despite sampling in an urban agglomeration, the chemical fingerprint of the aerosol is largely dictated by air mass origin rather than local sources. Springtime is characterized by the most elevated particulate levels due to the southerly air masses carrying particles from the Sahara Desert. Northerlies are observed throughout the year but are predominant during summer allowing the LRT source to peak (54 % during summer). Only during winter, due to extensive use of biomass combustion for domestic heating (36.6 % during winter), local sources dominate. A co-located online PMF source apportionment of submicron carbonaceous aerosols (Organic Aerosols, OA; Black Carbon) was performed by the means of an Aerosol Chemical Speciation Monitor (for OA) and an Aethalometer (for BC) for a four-month period. The comparison between the two methodologies allowed to better assess the robustness and limitations of the two methodologies. More specifically, LRT OA and biomass burning BC apportioned by the offline PMF showed a strong consistency with the online apportioned more oxidized oxygenated OA and BCwb, respectively; cross validating these sources. On the other hand, our traffic factor may contain additional hydrocarbon-like OA and BC from fossil fuel sources other than just vehicular emissions. Finally, the offline biomass burning OA source is likely to contain both primary and secondary OA.

Simple multi-residue analysis of persistent organic pollutants and molecular tracers in atmospheric samples.

We present a simple, selective and sensitive analytical method to quantitatively determine a wide range of halogenated persistent organic pollutants and molecular tracers in atmospheric samples. Identification and quantification was carried out by high-resolution gas chromatography, hyphenated with low-resolution mass spectrometry operating in electron impact (EI) and electron capture negative ionization (ECNI) mode. Optimization on a number of instrumental parameters was conducted to obtain ultra-trace detection limits, in the range of few fg/m3 for organohalogen compounds. Repeatability and reproducibility of the method was thoroughly evaluated. The analysis was validated with standard reference materials and successfully applied to actual atmospheric samples. The proposed multi-residue method provides a precise, affordable and practical procedure of sample analysis for environmental research laboratories with conventional instrumentation on a routine basis.•A simple combination of alumina, florisil and silica gel adsorbents was applied to sufficiently isolate polychlorinated biphenyls, organochlorine pesticides, polycyclic aromatic hydrocarbons, long chain n-alkanes, hopanes and steranes.•Full elution was achieved in two successive fractions, using small volumes of n-hexane and n-hexane/dichloromethane to recover all target substances.•To maximize analytical response, optimization was applied for three operating parameters in ECNI mode: i) ion source temperature; ii) emission current; and iii) electron energy.

Source apportionment of PM2.5 using organic/inorganic markers and emission inventory evaluation in the East Mediterranean-Middle East city of Beirut.

Source contributions to PM2.5 concentrations were evaluated in Greater Beirut (Lebanon), a typical East Mediterranean-Middle East (EMME) city, using Positive Matrix Factorization with two approaches. The first approach included only inorganic species (PMF-trad) and the other approach added organic markers (PMF-org). PMF-org identified 4 additional sources, and large discrepancies in contributions were observed for some major sources found in both approaches, highlighting the importance of including organic markers. The traffic factor was underestimated in PMF-trad by 2 to 7 folds. Moreover, results showed that this city is prone to high desert dust concentrations originating from uncontrollable dust storm events, like all cities in the Middle East. A PM2.5 mitigation plan taking into account the potency of the identified sources was developed. Sources like diesel generators or traffic presented smaller contributions in term of mass compared to desert dust, however the health impact of the latter is relatively small and actions should target sources with the highest potency. Local emission inventories in the EMME region are scarce and studies typically rely on global emission inventories for local air quality management plans, but these inventories significantly underestimate Beirut's road transport emissions by more than an order of magnitude.

Exposure to airborne SARS-CoV-2 in four hospital wards and ICUs of Cyprus. A detailed study accounting for day-to-day operations and aerosol generating procedures.

In any infectious disease, understanding the modes of transmission is key to selecting effective public health measures. In the case of COVID-19 spread, the strictness of the imposed measures outlined the lack of understanding on how SARS-CoV-2 transmits, particularly via airborne pathways. With the aim to characterize the transmission dynamics of airborne SARS-CoV-2, 165 and 62 air and environmental samples, respectively, were collected in four COVID-19 wards and ICUs in Cyprus and analyzed by RT-PCR. An alternative method for SARS-CoV-2 detection in air that provides comparable results but is less cumbersome and time demanding, is also proposed. Considering that all clinics employed 14 regenerations per hour of full fresh air inside patient rooms, it was hypothesized that the viral levels and the frequency of positive samples would be minimum outside of the rooms. However, it is shown that leaving the door opened in patient rooms hinders the efficiency of the ventilation system applied, allowing the virus to escape. As a result, the highest observed viral levels (135 copies m-3) were observed in the corridor of a ward and the frequency of positive samples in the same area was comparable to that inside a two-bed cohort. SARS-CoV-2 in that corridor was found primarily to lie in the coarse mode, at sizes between 1.8 and 10 µm. Similar to previous studies, the frequency of positive samples and viral levels were the lowest inside intensive care units. However, if a patient with sufficient viral load (Ct-value 31) underwent aerosol generating procedures, positive samples with viral levels below 45 copies m-3 were acquired within a 2 m distance of the patient. Our results suggest that a robust ventilation system can prevent unnecessary exposure to SARS-CoV-2 but with limitations related to foot traffic or the operations taking place at the time.

Evidence of stockpile contamination for legacy polychlorinated biphenyls and organochlorine pesticides in the urban environment of Cyprus (Eastern Mediterranean): Influence of meteorology on air level variability and gas/particle partitioning based on equilibrium and steady-state models.

The present study investigated comprehensively the atmospheric occurrence and fate of an extensive range of polychlorinated biphenyls (PCBs; forty-two congeners), organochlorine pesticides (OCPs; twenty-seven emerging and legacy agrochemicals) and polycyclic aromatic hydrocarbons (PAHs; fifty parent and alkylated members, including the non USEPA-16 listed toxic ones), in both gas and particulate phase of the scarcely monitored atmosphere over Cyprus for the first time. Parent-metabolite concentration ratios suggested fresh application for dichlorodiphenyl-trichloroethanes (DDTs), dicofol, hexachlorocyclohexanes, endosulfan and chlorothalonil, particularly during spring (April-May). Regressions of logarithms of partial pressure against ambient temperature revealed that secondary recycling from contaminated terrestrial surfaces regulates the atmospheric level variability of PCBs, DDTs, aldrin, chlordane, dicofol, heptachlor and endosulfan. Enthalpies of surface-air exchange (∆HSA) calculated from Clausius-Clapeyron equations were significantly correlated to vaporization enthalpies (∆HV) determined by chromatographic techniques, corroborating presence of potential stockpile-contaminated sites around the study area. The Harner-Bidleman equilibrium model simulating urban areas, and the Li-Jia empirical model, predicted better the partitioning behavior of PAHs (

Chemical profiles of PM2.5 emitted from various anthropogenic sources of the Eastern Mediterranean: Cooking, wood burning, and diesel generators.

The chemical profiles of PM2.5 emitted from a non-road diesel generator, wood burning and cooking activities including chicken and beef charcoal grilling and general cooking activities were determined. The characterization included the carbonaceous fraction (OC/EC), water-soluble ions, elements, and organic species comprising n-alkanes, polycyclic aromatic hydrocarbons, carboxylic acids, levoglucosan, dioxins, furans, and dioxin-like polychlorinated biphenyls. The main component in the PM2.5 from the different sources was carbonaceous matter with a mass contribution to PM2.5 of 49% for cooking activities, 53% for wood burning, 66% for beef grilling, 72% for chicken grilling, and 74% for diesel generator with different OC/EC concentration ratios. The analysis of organic compounds contents using diagnostic ratios and indexes showed differences between the sources and revealed specific source markers. The water-soluble ions had the highest contribution in the cooking activities profile with 17% of PM2.5 and the least in the chicken grilling profile (1.1%). Additionally, 29 analyzed elements were identified, and their contribution varied with the sources (ranging from 1% to 11% of PM2.5). These findings could be used to differentiate these sources and could assist in the use of source apportionment methods.

Model Calculations of Aerosol Transmission and Infection Risk of COVID-19 in Indoor Environments.

The role of aerosolized SARS-CoV-2 viruses in airborne transmission of COVID-19 has been debated. The aerosols are transmitted through breathing and vocalization by infectious subjects. Some authors state that this represents the dominant route of spreading, while others dismiss the option. Here we present an adjustable algorithm to estimate the infection risk for different indoor environments, constrained by published data of human aerosol emissions, SARS-CoV-2 viral loads, infective dose and other parameters. We evaluate typical indoor settings such as an office, a classroom, choir practice, and a reception/party. Our results suggest that aerosols from highly infective subjects can effectively transmit COVID-19 in indoor environments. This "highly infective" category represents approximately 20% of the patients who tested positive for SARS-CoV-2. We find that "super infective" subjects, representing the top 5-10% of subjects with a positive test, plus an unknown fraction of less-but still highly infective, high aerosol-emitting subjects-may cause COVID-19 clusters (>10 infections). 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, high-efficiency particulate air (HEPA) filtering. A particularly effective mitigation measure is the use of high-quality masks, which can drastically reduce the indoor infection risk through aerosols.

Chemical characterization of fine particles (PM2.5) at a coastal site in the South Western Mediterranean during the ChArMex experiment.

As part of the ChArMEx project (Chemistry-Aerosol Mediterranean Experiment, http://charmex.lsce.ipsl.fr), one year of continuous filter sampling was conducted from August 2012 to August 2013 at a rural (coastal) site in Algeria aiming to better document fine aerosol seasonal variability and chemical composition in the Southern part of the Mediterranean. Over 350 filters have been collected, weighted, and analyzed for the main ions and organic and elemental carbon. The obtained mass concentrations varied between 2.5 and 50.6 µg/m3 for PM2.5. The annual modulations of PM2.5 showed higher concentrations in the end summer 2012 and the early summer 2013 (28.50 µg/m3 in August 2012, 20.23 µg/m3 in September 2012, 20.19 µg/m3 in July 2013, and 17.88 µg/m3in August 2013). The particulate organic matter (POM) presented the greatest contribution (50%), followed by the secondary inorganic aerosols (SIA, 27%). The average organic carbon OC concentrations ranged from 1.66 to 6.05 µgC/m3. The average elemental carbon EC concentrations ranged from 0.92 to 3.49 µgC/m3 and contributed 7% of the PM2.5 mass to Bou-Ismail. The average value of the OC /EC ratio was close to 5.1 in Bou-Ismail, and was close to that found in Finokalia 4 (Greece 2004, 2006) but was lower than that of Montseny 11 (Spain 2002-2007) Western Mediterranean Basin (WMB). The concentrations of water-soluble organic carbon WSOC in the PM2.5 ranging from 0.66 to 3.70 µg/m3 recorded the minimum level in March 2013, and the maximum level in August 2012, with an average of 2.02 µg/m3.

Lung Antioxidant Depletion: A Predictive Indicator of Cellular Stress Induced by Ambient Fine Particles.

Regulations on ambient particulate matter (PM) are becoming more stringent because of adverse health effects arising from PM exposure. PM-induced oxidant production is a key mechanism behind the observed health effects and is heavily dependent on PM composition. Measurement of the intrinsic oxidative potential (OP) of PM could provide an integrated indicator of PM bioreactivity and could serve as a better metric of PM hazard exposure than PM mass concentration. The OP of two chemically contrasted PM2.5 samples was compared through four acellular assays, and OP predictive capability was evaluated in different cellular assays on two in vitro lung cell models. PM2.5 collected in Paris at a site close to the traffic exhibited a systematically higher OP in all assays compared to PM2.5 enriched in particles from domestic wood burning. Similar results were obtained for oxidative stress, expression of antioxidant enzymes, and pro-inflammatory chemokine in human bronchial epithelial and endothelial cells. The strongest correlations between OP assays and cellular responses were observed with the antioxidant (ascorbic acid and glutathione) depletion (OPAO) assay. Multivariate regression analysis from OP daily measurements suggested that OPAO was strongly correlated with polycyclic aromatic hydrocarbons at the traffic site while it was correlated with potassium for the domestic wood burning sample.

Effects of Atmospheric Processing on the Oxidative Potential of Biomass Burning Organic Aerosols.

Oxidative potential (OP), which is the ability of certain components in atmospheric particles to generate reactive oxidative species (ROS) and deplete antioxidants in vivo, is a prevailing toxicological mechanism underlying the adverse health effects associated with exposure to ambient aerosols. While previous studies have identified the high OP of fresh biomass burning organic aerosols (BBOA), it remains unclear how it evolves throughout atmospheric transport. Using the dithiothreitol (DTT) assay as a measure of OP, a combination of field observations and laboratory experiments is used to determine how atmospheric aging transforms the intrinsic OP (OPmassDTT) of BBOA. For ambient BBOA collected during the fire seasons in Greece, OPmassDTT was observed to increase by a factor of 2.1 ± 0.9 for samples of atmospheric ages up to 68 h. Laboratory experiments indicate that aqueous photochemical aging (aging by UVB and UVA photolysis; as well as OH oxidation), as well as aging by ozone and atmospheric dilution can transform the OPmassDTT of the water-soluble fraction of wood smoke within 2 days of atmospheric transport. The results from this work suggest that the air quality impacts of biomass burning emissions can extend beyond regions near fire sites and should be accounted for.

Stable isotopes measurements reveal dual carbon pools contributing to organic matter enrichment in marine aerosol.

Stable carbon isotope ratios in marine aerosol collected over the Southern Indian Ocean revealed δ13C values ranging from -20.0‰ to -28.2‰. The isotope ratios exhibited a strong correlation with the fractional organic matter (OM) enrichment in sea spray aerosol. The base-level isotope ratio of -20.0‰ is characteristic of an aged Dissolved Organic Matter (DOM) pool contributing a relatively homogeneous background level of DOM to oceanic waters. The range of isotope ratios, extending down to -28.2‰, is characteristic of more variable, stronger, and fresher Particulate Organic Matter (POM) pool driven by trophic level interactions. We present a conceptual dual-pool POM-DOM model which comprises a 'young' and variable POM pool which dominates enrichment in sea-spray and an 'aged' but invariant DOM pool which is, ultimately, an aged end-product of processed 'fresh' POM. This model is harmonious with the preferential enrichment of fresh colloidal and nano-gel lipid-like particulate matter in sea spray particles and the observed depleted δ13C ratio resulting from isotope equilibrium fractionation coupled with enhanced plankton photosynthesis in cold water (-2 °C to +8 °C). These results re-assert the hypothesis that OM enrichment in sea-spray is directly linked to primary production and, consequently, can have implications for climate-aerosol-cloud feedback systems.

Size-Resolved Identification, Characterization, and Quantification of Primary Biological Organic Aerosol at a European Rural Site.

Primary biological organic aerosols (PBOA) represent a major component of the coarse organic matter (OMCOARSE, aerodynamic diameter > 2.5 µm). Although this fraction affects human health and the climate, its quantification and chemical characterization currently remain elusive. We present the first quantification of the entire PBOACOARSE mass and its main sources by analyzing size-segregated filter samples collected during the summer and winter at the rural site of Payerne (Switzerland), representing a continental Europe background environment. The size-segregated water-soluble OM was analyzed by a newly developed offline aerosol mass spectrometric technique (AMS). Collected spectra were analyzed by three-dimensional positive matrix factorization (3D-PMF), showing that PBOA represented the main OMCOARSE source during summer and its contribution to PM10 was comparable to that of secondary organic aerosol. We found substantial cellulose contributions to OMCOARSE, which in combination with gas chromatography mass spectrometry molecular markers quantification, underlined the predominance of plant debris. Quantitative polymerase chain reaction (qPCR) analysis instead revealed that the sum of bacterial and fungal spores mass represented only a minor OMCOARSE fraction (<0.1%). X-ray photoelectron spectroscopic (XPS) analysis of C and N binding energies throughout the size fractions revealed an organic N increase in the PM10 compared to PM1 consistent with AMS observations.

Development of a repeated exposure protocol of human bronchial epithelium in vitro to study the long-term effects of atmospheric particles.

Chronic exposure to atmospheric particles is suspected of exacerbating chronic inflammatory respiratory diseases but the underlying mechanisms remain poorly understood. An experimental strategy using human bronchial epithelial cells (NHBE) known to be one of the main target cells of particles in the lung was developed to investigate the long term effects of repeated exposure to particles. Primary cultures of NHBE cells were grown at an air-liquid interface and subjected to repeated treatments to particles. Fate of particles, pro inflammatory response and epithelial differentiation were studied during the 5 weeks following the final treatment. Ultrastructural observations revealed the biopersistence of particles in the bronchial epithelium. The expression of cytochrome P450 1A1, was transiently induced, suggesting that organic compounds could have been metabolized. The release of GM-CSF and IL-6 (biomarkers of pro-inflammatory response), was induced by particle treatments and was maintained up to 5weeks after treatments. The release of amphiregulin and TGFα (Growth Factor) was induced after each treatment. The number of cells expressing the mucin MUC5AC, a differentiation marker, was increased in particle-exposed epithelium. The experimental strategy we developed is suitable for investigating in greater depth the long term effects of particles on bronchial epithelial cells repeatedly exposed to atmospheric particles in vitro.

The net effect of ultraviolet radiation on atmospheric dimethylsulphide over the Southern Indian Ocean.

Dimethylsulphide (DMS) in the atmosphere may play an important role in the climate system. This study shows an inverse relationship between ultraviolet extremes and atmospheric DMS, independent of changes in wind speed, sea-surface temperature and photosynthetically active radiation, as measured at Amsterdam Island in the Southern Indian Ocean.