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Our group is pursuing a volcanic ash transport model intercomparison study to evaluate the relative performance of several atmospheric transport models for selected case studies. These intercomparisons require the definition of standard output formats for producing results in a common framework. We define here the common format and develop a set of evaluation tools, allowing for side-by-side comparisons on a level playing field and providing a platform for further quantitative evaluation. The tools developed have widespread applicability to a number of ATM activities and are demonstrated in the realm of volcanic ash transport modelling. The Crater Peak, Mount Spurr eruption of 1992, Alaska, is used as a case study, employing HYSPLIT, FLEXPART and PUFF with common meteorological driving data, and with releases and intrinsic-model set-ups as similar as possible. [ABSTRACT FROM AUTHOR]

Highlights: [•] Atmospheric dispersion following a hypothetical accident in Sanmen NPP is simulated. [•] Japan, North Korea and Russia are slightly influenced in this accident. [•] In Taiwan and South Korea, population on 100% and 35% of the land should be given information about reducing dose. [•] In mainland China, about 284 thousand people are likely to get cancer. [ABSTRACT FROM AUTHOR]

The influence that the evolution of the ENSO cycle has on the moisture transport from the major oceanic moisture sources is investigated using a sophisticated Lagrangian approach informed by ERA-interim data, together with composites of ENSO phases. When maintaining the sources of moisture defined for the climatological period 1980-2012, the variations in the moisture sinks associated with each of these evaporative sources throughout the ENSO cycle reproduce the known patterns of variations of the large-scale atmospheric and precipitation systems over this cycle. Such variations include those observed in rainfall over the equatorial Pacific, in the major Summer monsoon systems, and in subtropical rainfall. When the areas of the sources were redefined according to the phase of ENSO, most of them remained stationary over the period of interest, nevertheless four of them showed notable differences in terms of their extents, namely the South Pacific and the Coral Sea (Pacific Ocean); the Mexican Caribbean (Atlantic), and the Arabian Sea (Indian). [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric concentration of Polychlorinated biphenyls (PCBs) were measured on diurnal basis by active air sampling during Dec 2006 to Feb 2007 in seven major cities from the northern (New Delhi and Agra), eastern (Kolkata), western (Mumbai and Goa) and southern (Chennai and Bangalore) parts of India. Average concentration of Σ25PCBs in the Indian atmosphere was 4460 (±2200) pg/m−3 with a dominance of congeners with 4–7 chlorine atoms. Model results (HYSPLIT, FLEXPART) indicate that the source areas are likely confined to local or regional proximity. Results from the FLEXPART model show that existing emission inventories cannot explain the high concentrations observed for PCB-28. Electronic waste, ship breaking activities and dumped solid waste are attributed as the possible sources of PCBs in India. Σ25PCB concentrations for each city showed significant linear correlation with Toxicity equivalence (TEQ) and Neurotoxic equivalence (NEQ) values. [Copyright &y& Elsevier]

Recent studies suggest that there is a strong linkage between the moisture uptake over the equatorial area of the Somali low level jet (SLLJ) and the rainfall variability over most of continental India. Additionally, the Madden-Julian Oscillation (MJO) strongly modulates the intraseasonal variability of the Indian summer monsoon rainfall, since the northward propagation of the boreal summer MJO is closely associated with the active and break phases of monsoon rainfall. But a question remains open: is there a relationship between the moisture transported by the SLLJ and the MJO evolution? In this paper, a Lagrangian approach is used to track the evaporation minus precipitation (E − P) evolution along trajectories of particles initially situated over the equatorial region of SLLJ. The impact of the MJO on the water budget transport of the SLLJ is examined by making composites of the obtained (E-P) fields for the different MJO phases. The spatial structures of the boreal summer intraseasonal oscillation are revealed in our results, which strongly suggest that the main responsible for the rainfall variability associated to the MJO in these regions are the changes in the moisture advected by the SLLJ. In order to assess the MJO-SLLJ interaction, an analysis of the total-column mass and the total-column specific humidity transported by the SLLJ during the MJO life cycle is performed. While a systematic difference between air mass advected to India during active and break phases of MJO is not detected, changes in the moisture of particles are found, with wet (dry) anomalies over enhanced (suppressed) convection region. This result implicitly leads to assume air-sea interaction processes. [ABSTRACT FROM AUTHOR]

Abstract: The analysis of concentrations of persistent organic pollutants (POPs) in ambient air is costly and can only be done for a limited number of samples. It is thus beneficial to maximize the information content of the samples analyzed via a targeted observation strategy. Using polychlorinated biphenyls (PCBs) as an example, a forecasting system to predict and evaluate long-range atmospheric transport (LRAT) episodes of POPs at a remote site in southern Norway has been developed. The system uses the Lagrangian particle transport model FLEXPART, and can be used for triggering extra (“targeted”) sampling when LRAT episodes are predicted to occur. The system was evaluated by comparing targeted samples collected over 12–25 h during individual LRAT episodes with monitoring samples regularly collected over one day per week throughout a year. Measured concentrations in all targeted samples were above the 75th percentile of the concentrations obtained from the regular monitoring program and included the highest measured values of all samples. This clearly demonstrates the success of the targeted sampling strategy. [Copyright &y& Elsevier]

Abstract: Episodes of exceptionally high surface ozone (O3) levels were measured in the Seoul Metropolitan Area (SMA) from July 6 to July 8. During the episode period, the 1-h average O3 concentration exceeded the daily maximum of 80 ppb over three consecutive days. In order to understand the mechanisms behind the increased O3 concentrations on consecutive days, several numerical experiments were conducted using the atmospheric dynamic model WRF for assessing the atmospheric flow as well as CMAQ for the estimation of the amount of photochemical ozone. Gradually increasing ozone concentration during episode period in SMA depends not only on the variation of meteorological conditions and the emission rate of precursors but also on the accompanying precursors within the air mass recirculation that are emitted from the SMA and its surrounding areas. The impact from the recirculation of precursors responsible for the increased ozone concentration was clarified for numerical studies using the particle dispersion model FLEXPART. Results obtained from our experimental model also demonstrated that recirculated O3 precursors such as nitrogen oxide (NO x) and volatile organic compounds (VOCs) significantly influenced O3 levels. During the episode period, NO x and VOCs concentrations in the PBL increased by an average of 2.9% and 19.7%, respectively, through recirculation. The recirculated precursors also are involved in the activation of photochemical reactions responsible for the formation of O3, leading to an average increase in the local O3 production of 10.9 ppb. And overall effect due to recirculation is dependent on the actual path and direction of recirculation. [Copyright &y& Elsevier]

Abstract: We investigate the source regions of the three polychlorinated biphenyl congeners (PCBs) 28, 101, and 180 measured at the Arctic stations Alert and Zeppelin, and at Birkenes, which is located in southern Norway. Although the Arctic is remote from the main use areas of these chemicals, PCBs have been found in Arctic air, seawater and biota, which has caused concerns for human and environmental health. We used 20-day backward calculations of the Lagrangian Particle Dispersion Model FLEXPART to identify the origin of air masses associated with the 20% highest and lowest measured PCB concentrations. At Birkenes, high concentrations are clearly associated with air masses arriving from known source regions (primarily in Europe and Russia), whereas low concentrations are correlated with atmospheric transport from regions with low primary emissions. At Zeppelin, the influence from known source regions is also enhanced when high PCB-28 and PCB-101 concentrations were measured. At Alert, in contrast, there is no clear link between high/low PCB concentrations and atmospheric transport from source/non-source regions. Additionally, we combined the atmospheric transport patterns with PCB emission data to identify important source regions and their seasonal variability. For the Arctic stations, Western Russia is the dominant source region for PCB-28 and PCB-101. Central Europe is the most important source region for PCB-180, but sources in the US contribute up to 15% to PCB-180 measured at Alert. [Copyright &y& Elsevier]

Although the identification of the moisture sources of a region is of prominent importance to characterize precipitation, the origin and amount of moisture towards the Indian Subcontinent and its relationship with the occurrence of precipitation are still not completely understood. In this article, the origin of the atmospheric water arriving to the Western and Southern India during a period of 5 years (1 January 2000-31 December 2004) is investigated by using a Lagrangian diagnosis method. This methodology computes budgets of evaporation minus precipitation by calculating changes in the specific humidity of thousands of air particles aimed to the study area following the observed winds. During the summer monsoon, the main supply of moisture is the Somali Jet, which crosses the equator by the West Indian Ocean. The recycling process is the main water vapour source in winter. Two additional moisture sources located over northwestern India and the Bay of Bengal are identified. A 30% increase in the moisture flux from the Indian Ocean has been related to the occurrence of strong precipitation in the area, and at the end of the monsoon, the recycling became a significant contribution to the last part of the wet season of Western and Southern India. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The vertical extension and the optical properties of aged ash layers advected from the Eyjafjallajökull volcanic eruption over the Eastern Mediterranean (Greece and Turkey) are presented for the period May 10–21, 2010. Raman lidar observations performed at three stations of EARLINET (Athens, Thessaloniki and Istanbul), provided clear ash signatures within certain layers, although ash was sometimes mixed with mineral dust advected from the Saharan region. AERONET columnar measurements did not indicate the presence of ash over the area for that period, although they did for the dust particles. This was further investigated and confirmed by simulations of the ash trajectories by the FLEXPART model and the BSC-DREAM8b dust model. Good agreement was found between simulated and observed geometrical characteristics of the ash and dust layers, respectively. Ash particles were observed over the lidar stations after 6–7-days transport from the volcanic source at height ranges between approximately 1.5 and 6 km. Mean ash particle layer thickness ranged between 1.5 and 2.5 km and the corresponding aerosol optical depth (AOD) was of the order of 0.12–0.06 at 355 nm and of 0.04–0.05 at 532 nm. Inside the ash layers, the lidar ratios (LR) ranged between 55 and 67 sr at 355 nm and 76–89 sr at 532 nm, while the particle linear depolarization ratio ranged between 10 and 25%. [Copyright &y& Elsevier]

Abstract: The Eyjafjallajökull ash that crossed over Spain and Portugal on 6–12 May 2010 has been monitored by a set of operational sun photometer sites within AERONET-RIMA and satellite sensors. The sun photometer observations (aerosol optical depth, coarse mode concentrations) and ash products from IASI and SEVIRI satellite sensors, together with FLEXPART simulations of particle transport, allow identifying the volcanic aerosols. The aerosol columnar properties derived from inversions were investigated, indicating specific properties, especially regarding the absorption. The single scattering albedo was high (0.95 at 440 nm) and nearly wavelength independent, although with slight decrease with wavelength. Other parameters, like the fine mode fraction of the volume size distributions (0.20–0.80) or the portion of spherical particles (15–90%), were very variable among the sites and indicated that the various ash clouds were inhomogeneous with respect to particle size and shape. [Copyright &y& Elsevier]

Abstract: This work shows how ambient radon concentrations measured at Cabauw station in central Netherlands are influenced by transport from different regions under typical transport conditions occurring during April and November, 2007 by means of atmospheric Lagrangian particle dispersion modelling in a receptor-oriented approach. Four specific regions have been isolated to assess their contribution to the modelled radon ambient concentrations at Cabauw, and two different radon flux assumptions. Westerly flows coming from the ocean are poor in radon and do not increase radon air concentrations unless there is some fetch over the British Isles. Continental transport, mainly from eastern and southern Europe, significantly increases radon background concentrations, reaching increments of 3 Bq m−3. A constant 0.66 atoms cm−2 s−1 radon flux over land and zero over water bodies is a good approximation for the source term in order to study regional contributions and modulation of the radon background. [Copyright &y& Elsevier]

An abstract of the article "Application of Lagrangian particle dispersion models to air quality assessment in the Trans-Manche region of Nord-Pas-de-Calais (France) and Kent (Great Britain)," by S. Plainiotis and colleagues is presented.

Atmospheric fine-particle (PM 2.5) pollution is a prominent regional issue that is affected by local emissions, regional transport, and secondary formation and impacts human health, air quality, and climate. Identifying the origin and types of pollution sources that are transported to the receptor site is essential for the development of joint prevention and control measures. This study developed a combined method to explore the source-receptor relationship during haze episodes of the heating season in Beijing, by combining positive matrix factorization (PMF) model with Lagrangian particle model (FLEXPART-WRF) and chemical transport model (CAMx). Six source types identified by PMF with high-time-resolution online measurements were counted in different transport pathways including local, south, east, and north. The results showed that secondary source contributed the most to PM 2.5 , which was affected by regional transport of Baoding, Langfang, and Tangshan. Among major primary sources, vehicle source was concentrated locally. Coal combustion contributed a higher proportion locally (15.8%) and in the south (15.0%), and Baoding, Langfang, and Xingtai along the Taihang Mountains were predominant potential source regions. Biomass burning contributed a higher proportion in the south (19.0%) and northeast (22.6%), and adjacent southern Hebei and Northeastern areas were the predominant potential source regions. Moreover, the variations in PM 2.5 sources, footprints, and source regions of two haze cases from pre-pollution to dissipation were analyzed. EP1, with a more southern transport, was caused by high secondary source and coal combustion, while EP2 was characterized by secondary source and biomass burning from Hebei and Liaoning Province transport. In particular, the emission distribution of surrounding cities along transport pathways had an important effect on PM 2.5 sources in Beijing. This study demonstrated that the combined method can provide guidance for implementing effective emission mitigation measures and improving the regional air quality. • A coupled method combing receptor model with air quality model is developed. • Contribution of six PM 2.5 sources in different transport pathway was quantified. • Potential source regions of primary or secondary sources can be distinguished. • Regional transport from the south contributed notably to secondary sources in Beijing. [ABSTRACT FROM AUTHOR]

Ground-based observations of ozone have been performed at three sites in northern Fennoscandia, Karasjok, Esrange and Pallas. The sites are located in remote, unpolluted areas far away from the European source regions, and thus representing the northern hemispheric background. Events of photochemical episodes are rare. However, on 19 and 20 April 2003 two episodes with unusually high ozone values were measured at these stations. The highest values of 85. 4 and 83. 5ppbv were observed at Esrange and Pallas, respectively, on the 20th April. A simultaneous increase of other pollutants, e. G. Nitrate, supports the idea that this was an anthropogenic episode to the far north. A third episode was seen on the 21st at Esrange and Pallas but not at Karasjok. Results from a source–receptor analysis with the particle dispersion model FLEXPART show southern continental Europe as the main source of the polluted air masses in connection with the enhanced ozone, whereas in between transport of cleaner air masses from the North-Atlantic took place. The highest ozone peaks measured at Esrange and Pallas can most likely be traced back to transport of pollution from the Iberian peninsula superimposed on pollution transported from the Northern Mediterranean. [Copyright &y& Elsevier]

Abstract: Meteorological condition in coastal regions is diurnally variable and spatially heterogeneous due to complex topography, land–sea interface, etc. A wide range of dispersion conditions is possible on a given day in the coastal regions. In case of inadvertent accidental situations, though unlikely, it would be necessary to examine the potentially severe case among different dynamically occurring local atmospheric conditions for dispersion and its range of impact around a nuclear power plant for safety analysis. In this context, dispersion of air borne radioactive effluents during a hypothetical accidental scenario from a proposed prototype fast breeder reactor (PFBR) at an Indian coastal site, Kalpakkam, is simulated using a 3-D meso-scale atmospheric model MM5 and a random walk particle dispersion model FLEXPART. A simulation carried out for a typical summer day predicted the development of land–sea breeze circulation and thermal internal boundary layer (TIBL) formation, which have been confirmed by meteorological observations. Analysis of dose distribution shows that the maximum dose for releases from a 100m stack occurs at two places within 4km distance during sea breeze/TIBL fumigation hours. Maximum dose also occurred during nighttime stable conditions. Results indicate that, on the day of present study, the highest concentrations occurred during periods of TIBL fumigation rather than during stable atmospheric conditions. Further, the area of impact (plume width at the surface) spreads up to a down wind distance of 4km during fumigation condition. Simulation over a range of 25km has shown turning of plume at the incidence of sea breeze circulation and two different dispersion patterns across the sea breeze front. These results are significant in comparison to the expected pattern shown by Gaussian plume model used for routine analysis. [Copyright &y& Elsevier]

Two radon measurement stations located to the north and south of a NORM (Naturally Occurring Radioactive Materials) repository of phosphogypsum (southwest of Europe) were used to monitor radon behavior during 2018. The stations are located at opposing sides of the repository, one in Huelva City to the north and other one in a rural area to the south. This setup aimed to identify the influence of the NORM repository on each station and use radon levels as a marker of atmospheric transport in the local area. To achieve this, a comparison was carried out with other coastal stations in the south of Spain, finding higher average concentrations in Huelva City, ~3.3 Bq m−3. Hierarchical clustering was applied to identify days with different radon patterns at each Huelva station, detecting possible local radon transport events from the repository. Three events were investigated with WRF (Weather Research and Forecasting) and FLEXPART-WRF (FLEXible PARTicle dispersion model). It was found that both sampling sites required atmospheric stagnant conditions to reach high radon concentration. However, under these conditions the urban station showed high radon regardless of wind direction while the rural station also required radon transport from the repository, either directly or indirectly. [Display omitted] • One-year of radon observations in two stations (SW of Europe) were studied. • Urban and rural stations located at opposing sides of a phosphogypsum repository. • Atmospheric stagnant conditions favored high radon at the urban station. • Rural site required atmospheric stagnation and radon transport from the repository. • The repository modulates radon concentrations in this region. [ABSTRACT FROM AUTHOR]

In the event of an accidental or intentional hazardous material release in the atmosphere, researchers often run physics-based atmospheric transport and dispersion models to predict the extent and variation of the contaminant spread. These predictions are imperfect due to propagated uncertainty from atmospheric model physics (or parameterizations) and weather data initial conditions. Ensembles of simulations can be used to estimate uncertainty, but running large ensembles is often very time consuming and resource intensive, even using large supercomputers. In this paper, we present a machine-learning-based method which can be used to quickly emulate spatial deposition patterns from a multi-physics ensemble of dispersion simulations. We use a hybrid linear and logistic regression method that can predict deposition in more than 100,000 grid cells with as few as fifty training examples. Logistic regression provides probabilistic predictions of the presence or absence of hazardous materials, while linear regression predicts the quantity of hazardous materials. The coefficients of the linear regressions also open avenues of exploration regarding interpretability—the presented model can be used to find which physics schemes are most important over different spatial areas. A single regression prediction is on the order of 10,000 times faster than running a weather and dispersion simulation. However, considering the number of weather and dispersion simulations needed to train the regressions, the speed-up achieved when considering the whole ensemble is about 24 times. Ultimately, this work will allow atmospheric researchers to produce potential contamination scenarios with uncertainty estimates faster than previously possible, aiding public servants and first responders. [ABSTRACT FROM AUTHOR]

Fine particulate matter (PM2.5) has a serious impact on human health. Forecasting PM2.5 levels and analyzing the pollution sources of PM2.5 are of great significance. In this study, the Lagrangian particle dispersion (LPD) model was developed by combining the FLEXPART model and the Bayesian inventory optimization method. The LPD model has the capacity for real-time forecasting and determination of pollution sources of PM2.5, which refers to the contribution ratio and spatial distribution of each type of pollution (industry, power, residential, and transportation). In this study, we applied the LPD model to the Beijing-Tianjin-Hebei (BTH) region to optimize the a priori PM2.5 emission inventory estimates during 15–20 March 2018. The results show that (1) the a priori estimates have a certain degree of overestimation compared with the a posteriori flux of PM2.5 for most areas of BTH; (2) after optimization, the correlation coefficient (R) between the forecasted and observed PM2.5 concentration increased by an average of approximately 10%, the root mean square error (RMSE) decreased by 30%, and the IOA (index of agreement) index increased by 16% at four observation sites (Aotizhongxin_Beijing, Beichenkejiyuanqu_Tianjin, Dahuoquan_Xintai, and Renmingongyuan_Zhangjiakou); and (3) the main sources of pollution at the four sites mainly originated from industrial and residential emissions, while power factory and transportation pollution accounted for only a small proportion. The concentration of PM2.5 forecasts and pollution sources in each type of analysis can be used as corresponding reference information for environmental governance and protection of public health. [ABSTRACT FROM AUTHOR]

Power plant's site selection is a complex task and involves through analyses of multi-disciplinary processes which are interlinked with each other. The site selection for nuclear power plants additionally requires an assessment of radiation doses to the environment and public during normal operation and in the case of an accident. This demands the problem of radioactive particles' dispersion in atmosphere to be analysed in real time for a comprehensive set of radioactive release scenarios in prevailing meteorological conditions in the plant surroundings. In this study, a local scale atmospheric dispersion problem, considering a hypothetical accidental release (1 Bq s -1 of I-131) from a nuclear power plant is simulated with a combination of weather forecasting and particle dispersion codes on a multiprocessor computer system. The meteorological parameters are predicted with a weather research and forecasting (WRF) model and used in Lagrangian particle dispersion model based code FLEXPART to calculate the trajectory of released particles, and thereby, the estimation of spatial I-131 dose distribution. The concentration of particles and radiation doses were calculated for release heights of 10, 57, and 107 m and found in a reasonable agreement with the observed data and better than an earlier investigation done with regional atmospheric modelling system (RAMS) code. A comparison between the results of WRF and RAMS for various meteorological parameters revealed that better space-time predictions of wind speeds and directions by WRF had a profound effect on tracing the trajectories of particles and thereby the spatial dose distribution. The particles followed the changes in wind direction predicted by WRF that were known to prevail in the region., (© 2021 Society for Radiological Protection. Published on behalf of SRP by IOP Publishing Limited. All rights reserved.)

Local emission and long-range transport impacts on the observed concentrations (dry air mole fractions) of CO, CO 2 , and CH 4 have been investigated using three years (April 2016 to April 2019) of surface measurements at a tropical rural site, Gadanki (13.5° N, 79.2° E) in Southern peninsular India. Gadanki represents the poor coverage area of Greenhouse Gas (GHG) measurements in India and has both local emission and long-range transport influences on its air masses. All the three gases have shown strong seasonality and diurnal variations. Trend analysis showed a significant decreasing trend in CO (14.3 ± 0.2 ppbv/year) and increasing trends in CO 2 (2.5 ± 1.2 ppmv/year) and CH 4 (11.1 ± 0.03 ppbv/year). CO 2 and CH 4 trends are marginally higher than the global trends (2.2 ± 0.004 ppmv/year and 7.0 ± 0.001 ppbv/year, respectively) for the same period highlighting the sustained local emission impact on the observed concentrations. Among the three species, CO has been the most local emission impacted species with local emission contribution (to the total observed concentration) varying between 4 and 25% during different seasons with a median value always lying above 10% irrespective of the season. In the case of CO 2 and CH 4 , the local emission contribution found to vary in the range of 0.8–7% and 0.15–3%, respectively. Long-range transport impact dominance over the local emission is observed in CO 2 and CH 4 during all the seasons. Analysis using MODIS fire count data, Concentration Weighted Trajectory (CWT) and FLEXPART have reconfirmed the combined effect of local and long-range transport impacts on the observed concentrations. Comparison of the IASI MetOp and AIRS satellite data products with surface measurements showed the significant bias and poor representation of the seasonality demonstrating the limitations on the sensitivity of satellite trace gas measurements within the boundary layer. [Display omitted] • Local emission and long-range transport impacts on CO, CO 2 , and CH 4 have been investigated at a tropical rural site. • CO has been the most local emission impacted species among the three. • Forest fires, agricultural residue and biomass burning have been the dominant local sources. • Trend analysis showed a significant decreasing trend in CO and increasing trends in CO 2 and CH 4. • Comparison of satellite data with surface measurements showed a significant difference. [ABSTRACT FROM AUTHOR]

Online Nuclear Emergency Response System (ONERS) is a GIS based Decision Support System developed for the management of Off-Site Nuclear Emergencies at Nuclear Power Plant (NPP) sites in India. As part of this development, the FLEXPART model is modified to compute atmospheric dispersion using observations from the local meteorological tower for the estimation of concentration and radiological dose over short-range range in realtime. In this work, the modified FLEXPART is validated for dose assessments using gamma dose rate measurements by Autonomous Gamma Dose Loggers installed around the Pressurized Heavy Water Reactor (PHWR) of Madras Atomic Power Station (MAPS) at Kalpakkam site in southeast India. The plume exposure dose is computed in two pathways i) cloudshine dose by incorporating a point kernel algorithm ii) submersion dose by semi-infinite plume method using FLEXPART. Comparison of model estimates with detector data for the 8-day period (01–08 December 2017) covering various atmospheric conditions indicates that the simulated cloud gamma dose rate is in good agreement with observed dose under stable, neutral, and unstable conditions with a coefficient of determination of 0.66, 0.73 and 0.49 respectively. The overestimation of dose under unstable conditions could be due to underestimation of mixed layer height (h) and convective velocity scale (w*) computed using the local similarity approach while using tower data, which needs further insights for improvements. Fig. Comparison of simulated 3D cloud gamma dose rates with measurements for a few days starting from December 1, 2017 to December 8, 2017. [Display omitted] • Modification of FLEXPART to take local tower observation. • Estimation of similarity parameters using tower observations. • Comparison of simulated dose rate with measurements using radiation detectors. • Optimization of grid configuration for submersion dose calculation. [ABSTRACT FROM AUTHOR]

Year-round carbon dioxide (CO 2) and methane (CH 4) concentration measurements, performed for the first time in the city of Athens, Greece from December 21, 2018 to December 31, 2019, are presented in this study and analyzed in relation to atmospheric circulation patterns at a local, regional and long-range transport scale. Clear diurnal and seasonal variations of both greenhouse gases were detected. The observed increased levels during night and early morning hours are attributed to traffic/heating emissions and leakages of residential natural gas for CO 2 and CH 4 , respectively. Using CO 2 and CH 4 levels simultaneously measured at the regional background site at Finokalia (Greece), increments in their levels due to local and regional anthropogenic sources within the city were assessed. For CO 2 , maximum and minimum increments were clearly observed during winter and summer respectively, suggesting a greater impact of combustion of fossil fuel and especially of biomass on CO 2 levels during winter. On the other hand, CH 4 increments were similar in all seasons, suggesting that local sources of CH 4 remain quite constant year-round. Through the implementation of the Conditional Probability Function (CPF), the emission sources of theses greenhouse gases have been localized to the northern and the eastern domains of the Athens basin. Stagnant atmospheric conditions were also associated with an increased likelihood of CO 2 and CH 4 episodes. Backward modeling simulations with FLEXPART and HYSPLIT models indicate an industrial zone and a petrochemical zone, situated to the north and to the west of Athens respectively, as possible CH 4 regional sources as well as possible CO 2 contributions from southern directions attributed to shipping emissions from the port of Piraeus. The present study provides knowledge needed for the determination of greenhouse gas emission mitigation strategies in Athens. [Display omitted] • Clear diurnal variability for both GHGs. • Enhanced CO 2 levels during winter nighttime due to combustion processes. • Local CH 4 sources remain quite constant throughout the year. • Additional anthropogenic burden from urban CO 2 emissions during winter around 6%. • Regional CH 4 sources from industrial/petrochemical zones enhancing levels. [ABSTRACT FROM AUTHOR]

This study aims to improve the understanding of the role of the Madden-Julian Oscillation (MJO) in modulating the midsummer drought (MSD) in Mexico. First, the main moisture sources for the MSD region in Mexico during the summer were identified using the Lagrangian particle dispersion model FLEXPART for the period 1979–2017. From this analysis, the Caribbean Sea was identified as one of the main moisture sources, particularly the area where the core of the Caribbean low-level jet (CLLJ) is located. Second, the water vapour flux transported by the CLLJ to Mexico was then analysed. It was found that the summer seasonal cycle of the CLLJ is associated with the bimodal precipitation pattern in Mexico through the seasonal variability of the moisture contribution from the CLLJ to precipitation over the MSD region, thereby confirming the CLLJ as a key element in the occurrence of the MSD in the Americas. Third, the influence of the MJO on this transport was examined. This analysis showed that the locally dry phases of the MJO decrease the contribution of moisture from the CLLJ core towards the MSD region, while the locally wet phases increase it. Moreover, phases 1 and 2 of the MJO were found to influence the first precipitation peak that occurs in the southwestern region of Mexico by increasing the contribution of moisture from the northeastern tropical Pacific. The study ends by proposing, for the first time, a mechanism by which the MJO modulates the MSD in Mexico. • The moisture flux balance over the MSD region in Mexico during summer, associated with the freshwater flux transported by the CLLJ towards Mexico, is analysed. • The influence of the MJO on the freshwater flux transported by the CLLJ towards the MSD region in Mexico is examined. • A better understanding of the role of the MJO in modulating the MSD in Mexico is obtained, and a mechanism by which the MJO modulates it is proposed. [ABSTRACT FROM AUTHOR]

Xenobiotic chemical emissions from the informal electronic waste recycling (EW) sector are emerging problem for developing countries, with scale and impacts that are yet to be evaluated. We report an intensive polyurethane foam disk passive air sampling study in four megacities in India to investigate atmospheric organic pollutants along five transects viz., EW, information technology (IT), industrial, residential, and dumpsites. Intraurban emission sources were estimated and attributed by trajectory modeling and positive matrix factorization (PMF). ∑ 17 PCDD/Fs, ∑ 25 PCBs, ∑ 7 plasticizers, and ∑ 15 PAHs concentrations ranged from 3.1 to 26 pg/m 3 (14 ± 7; Avg ± SD), 0.5-52 ng/m 3 (9 ± 12); 7.5-520 ng/m 3 , (63 ± 107) and 6-33 ng/m 3 (17 ± 6), respectively. EW contributed 45% of total PCB concentrations in this study and was evidenced as a major factor by PMF. The dominance of dioxin-like PCBs (dl-PCBs), particularly PCB-126, reflects combustion as the possible primary emission source. PCDD/Fs, PCBs and plasticizers were consistently highest at EW transect, while PAHs were maximum in industrial transect followed by EW. Concentrations of marker plasticizers (DnBP and DEHP) released during EW activities were significantly higher ( p < 0.05) in Bangalore than in other cities. Toxic equivalents (TEQs) due to dl-PCBs was maximum in the EW transect and PCB-126 was the major contributor. For both youth and adult, the highest estimated inhalation risks for dl-PCBs and plasticizers were seen at the EW transect in Bangalore, followed by Chennai and New Delhi.

Facing serious air pollution problems, the Chinese government has taken numerous measures to prevent and control air pollution. Understanding the sources of pollutants is crucial to the prevention of air pollution. Using numerical simulation method, this study analysed the contributions of the total local emissions and local emissions from different sectors (such as industrial, traffic, resident, agricultural, and power plant emissions) to PM 2.5 concentration, backward trajectory, and potential source regions in Tangshan, a typical heavy industrial city in north China. The impact of multi-scale meteorological conditions on source apportionment was investigated. From October 2016 to March 2017, total local emissions accounted for 46.0% of the near-surface PM 2.5 concentration. In terms of emissions from different sectors, local industrial emissions which accounted for 23.1% of the near-surface PM 2.5 concentration in Tangshan, were the most important pollutant source. Agricultural emissions were the second most important source, accounting for 10.3% of the near-surface PM 2.5 concentration. The contributions of emissions from power plants, traffic, residential sources were 2.0%, 3.0%, and 7.2%, respectively. The contributions of total local emissions and emissions from different sectors depended on multi-scale meteorological conditions, and static weather significantly enhanced the contribution of regional transport to the near-surface PM 2.5 concentration. Eight cluster backward trajectories were identified for Tangshan. The PM 2.5 concentration for the 8 cluster trajectories significantly differed. The near-surface PM 2.5 in urban Tangshan (receptor point) was mainly from the local emissions, and another important potential source region was Tianjin. The results of the source apportionment suggested the importance of joint prevention and control of air pollution in some areas where cities or industrial regions are densely distributed. Image 1 • The contribution of local and different sectors emissions on PM 2.5 concentration. • Backward trajectory and potential source regions of PM 2.5. • The impact of multi-scale meteorological conditions on source apportionment. • Local emissions accounted for 46.0% of the near-surface PM 2.5 concentration. • Static weather significantly enhanced the contribution of regional transport. The contributions of local emissions depended on multi-scale meteorological conditions, and static weather significantly enhanced the contribution of regional transport in Tangshan. [ABSTRACT FROM AUTHOR]

In this study, the seasonal mean PM 2.5 concentration in Qingdao, a coastal city, during 2014–2018 was first analyzed and the winter, in particular of 2015, showed the highest concentration. To elucidate the sources and control factors of PM 2.5 , three dimensional model Weather Research and Forecasting (WRF), Community Multiscale Air Quality model (CMAQ), as well as Flexible Particle model (FLEXPART), were used. During December 2015 and January 2016, modeling results showed that the mean contribution to PM 2.5 mass concentrations from local emissions in Qingdao was 25%, and the transport from north and west accounted for almost half. Over the two episodically polluted periods (29–31 December 2015; 15–17 January 2016), the local emissions in Qingdao surprisingly contributed to only 18% and 24% to PM 2.5 mass concentrations, respectively, indicating the dominant contributions from other regions, such as areas outside Qingdao in Shandong and Beijing-Tianjin-Hebei (BTH). The results show the sources region and contribution may vary remarkably along with the change in the pathways of the air parcel, inferred by the FLEXPART, while the near-surface PM 2.5 enhancement is largely caused by downward vertical advection and enhanced aerosol chemistry reactions, accompanied by simultaneous drop in the boundary layer height. This study also reveals that the transport contribution is sensitive to the air parcel trajectories. We, therefore, recommend the efficient emission control based on transport trajectories in short-term air quality improvement in Qingdao. • The local emission in Qingdao only contributed on average of one fourth during winter 2015. • The transport plays a major role in modulating the air pollution in Qingdao. • The sources of PM2.5 in Qingdao may vary dramatically in a short period of time. [ABSTRACT FROM AUTHOR]

Identifying and quantifying the major sources of atmospheric particulate matter (PM) is essential for the development of pollution mitigation strategies to protect public health. However, urban PM is affected by local primary emissions, transport, and secondary formation; therefore, advanced methods are needed to elucidate the complex sources and transport patterns. Here, an improved source apportionment method was developed by incorporating the receptor model, Lagrangian simulation, and emissions inventories to quantify PM 2.5 sources for an industrial city in China. PM 2.5 data including ions, metals, organic carbon, and elemental carbon were obtained by analyzing 1 year of sampling results at urban and rural sites. This method identified coal combustion (30.64%), fugitive dust (13.25%), and vehicles (12.51%) as major primary sources. Secondary sources, including sulfate, nitrate, and secondary organic aerosols also contributed strongly (25.28%–30.76% in total) over urban and rural areas. Hebei Province was the major regional source contributor (43.05%–57.51%) except for fugitive dust, on which Inner Mongolia had a greater impact (43.51%). The megacities of Beijing and Tianjin exerted strong regional impacts on the secondary nitrate and secondary organic aerosols factors, contributing 11.32% and 15.65%, respectively. Pollution events were driven largely by secondary inorganic aerosols, highlighting the importance of reducing precursor emissions at the regional scale, particularly in the Beijing–Tianjin–Hebei region. Overall, our results demonstrate that this novel method offers good flexibility and efficiency for quantifying PM 2.5 sources and regional contributions, and that it can be extended to other cities. Unlabelled Image • An improved source apportionment method combining receptor model and Lagrangian simulations was proposed. • PM 2.5 in the case city was apportioned to 7 primary factors and 3 secondary factors. • Different transport patterns were estimated for various sources. • Hebei Province was the most influential source region of secondary sources. [ABSTRACT FROM AUTHOR]

Ambient air concentrations and bulk deposition of polychlorinated dibenzo- p -dioxins and dibenzo–furans (PCDD/F) were monitored at three high Alpine stations in Germany (Schneefernerhaus/Zugspitze: 2650 m a.s.l.), Switzerland (Weiβfluhjoch: 2663 m a.s.l.), and Austria (Sonnblick Observatory: 3106 m a.s.l.) from 2005 to 2018. High-volume active air samplers were selectively in operation on a daily basis according to predicted source-regions of air masses. Air concentrations showed only small differences between the three sites and were one or two orders of magnitude lower than in urbanized areas in central Europe. Calculation of source contribution revealed waste incineration, heating, and coal combustion as major sources of PCDD/F in ambient air. Air masses from the northeast were characterized by higher concentrations of PCDD/F than those from northwest and south. However, air masses from the northeast source region are significantly less frequent at the three Alpine stations than air masses from the other source regions. Only at Schneefernerhaus, the majority of congeners exhibit a clear decreasing temporal trend in ambient air concentrations. Deposition rates of PCDD/F measured at the three stations were almost as high as at monitoring stations in urban agglomerations. Despite lower precipitation rates in the central Alps, deposition of PCDD/F was higher at the Sonnblick Observatory than in the Northern Alps (Schneefernerhaus). Bulk deposition for Weiβfluhjoch and Schneefernerhaus exhibit a decreasing temporal trend. • Alpine concentrations of PCDD/F in ambient air distinguishing four source regions. • Air concentrations 1–2 orders of magnitude lower than in urbanized European areas. • Partly decreasing temporal trends of ambient air concentrations but levelling of. • Deposition rates in the same order of magnitude like at urban agglomerations. • Domestic heating, coal burning and waste incineration as dominant sources. [ABSTRACT FROM AUTHOR]