Pollution Plume Research Articles

Sources and variations of tropospheric ozone in central Siberia: observations and model simulations

Impact of climatically significant anthropogenic and natural emissions to seasonal ozone (O3) variations observed at the Zotino Tall Tower Observatory (ZOTTO) in central Siberia in 2007–2012 have quantitatively been estimated using GEOS-Chem chemical transport model. It is shown that the formation of a stable continental pollution plume from sources in Western Europe, European Russia, and southern Siberia plays an important role in regional balance of near-surface ozone and allows to explain up to 15%–17% of the amplitude of O3 annual cycle observed at ZOTTO (∼5–6 ppb).

Non-methane hydrocarbon (NMHC) fingerprints of major urban and agricultural emission sources for use in source apportionment studies

Abstract. In complex atmospheric emission environments such as urban agglomerates, multiple sources control the ambient chemical composition driving air quality and regional climate. In contrast to pristine sites, where reliance on single or a few chemical tracers is often adequate for resolving pollution plumes and source influences, the comprehensive chemical fingerprinting of sources using non-methane hydrocarbons (NMHCs) and the identification of suitable tracer molecules and emission ratios becomes necessary. Here, we characterise and present chemical fingerprints of some major urban and agricultural emission sources active in South Asia, such as paddy stubble burning, garbage burning, idling vehicular exhaust and evaporative fuel emissions. A total of 121 whole air samples were actively collected from the different emission sources in passivated air sampling steel canisters and then analysed for 49 NMHCs (22 alkanes, 16 aromatics, 10 alkenes and one alkyne) using thermal desorption gas chromatography flame ionisation detection. Several new insights were obtained. Propane was found to be present in paddy stubble fire emissions (8 %), and therefore, for an environment impacted by crop residue fires, the use of propane as a fugitive liquefied petroleum gas (LPG) emission tracer must be done with caution. Propene was found to be ∼ 1.6 times greater (by weight) than ethene in smouldering paddy fires. Compositional differences were observed between evaporative emissions of domestic LPG and commercial LPG, which are used in South Asia. While the domestic LPG vapours had more propane (40 ± 6 %) than n-butane (19 ± 2 %), the converse was true for commercial LPG vapours (7 ± 6 % and 37 ± 4 %, respectively). Isoprene was identified as a new tracer for distinguishing paddy stubble and garbage burning in the absence of isoprene emissions at night from biogenic sources. Analyses of source-specific inter-NMHC molar ratios revealed that toluene/benzene ratios can be used to distinguish among paddy stubble fire emissions in the flaming (0.38 ± 0.11) and smouldering stages (1.40 ± 0.10), garbage burning flaming (0.26 ± 0.07) and smouldering emissions (0.59 ± 0.16), and traffic emissions (3.54 ± 0.21), whereas i-pentane ∕ n-pentane can be used to distinguish biomass burning emissions (0.06–1.46) from the petrol-dominated traffic and fossil fuel emissions (2.83–4.13). i-butane ∕ n-butane ratios were similar (0.20–0.30) for many sources and could be used as a tracer for photochemical ageing. In agreement with previous studies, i-pentane, propane and acetylene were identified as suitable chemical tracers for petrol vehicular and evaporative emissions, LPG evaporative and vehicular emissions and flaming-stage biomass fires, respectively. The secondary pollutant formation potential and human health impact of the sources was also assessed in terms of their hydroxyl radical (OH) reactivity (s−1), ozone formation potential (OFP; gO3/gNMHC) and fractional benzene, toluene, ethylbenzene and xylenes (BTEX) content. Petrol vehicular emissions, paddy stubble fires and garbage fires were found to have a higher pollution potential (at ≥95 % confidence interval) relative to the other sources studied in this work. Thus, many results of this study provide a new foundational framework for quantitative source apportionment studies in complex emission environments.

Identification of key aerosol types and mixing states in the central Indian Himalayas during the GVAX campaign: the role of particle size in aerosol classification

Studies in aerosol properties, types and sources in the Himalayas are important for atmospheric and climatic issues due to high aerosol loading in the neighboring plains. This study uses in situ measurements of aerosol optical and microphysical properties obtained during the Ganges Valley Aerosol eXperiment (GVAX) at Nainital, India over the period June 2011–March 2012, aiming to identify key aerosol types and mixing states for two particle sizes (PM1 and PM10). Using a classification matrix based on SAE vs. AAE thresholds (scattering vs. absorption Ångström exponents, respectively), seven aerosol types are identified, which are highly dependent on particle size. An aerosol type named “large/BC mix” dominates in both PM1 (45.4%) and PM10 (46.9%) mass, characterized by aged BC mixed with other aerosols, indicating a wide range of particle sizes and mixing states. Small particles with low spectral dependence of the absorption (AAE < 1) account for 31.6% and BC-dominated aerosols for 14.8% in PM1, while in PM10, a large fraction (39%) corresponds to “large/low-absorbing” aerosols and only 3.9% is characterized as “BC-dominated”. The remaining types consist of mixtures of dust and local emissions from biofuel burning and display very small fractions. The main optical properties e.g. spectral scattering, absorption, single scattering albedo, activation ratio, as well as seasonality and dependence on wind speed and direction of identified types are examined, revealing a large influence of air masses originating from the Indo-Gangetic Plains. This indicates that aerosols over the central Himalayas are mostly composed by mixtures of processed and transported polluted plumes from the plains. This is the first study that identifies key aerosol populations in the central Indian Himalayas based on in situ measurements and the results are highly important for aerosol-type inventories, chemical transport models and reducing the uncertainty in aerosol radiative forcing over the third pole.

In Situ Aircraft Measurements of CO2 and CH4: Mapping Spatio-Temporal Variations over Western Korea in High-Resolutions

A cavity ring-down spectroscopy (CRDS) G-2401m analyzer onboard a Beechcraft King Air 350, a new Korean Meteorological Administration (KMA) research aircraft measurement platform since 2018, has been used to measure in situ CO2, CH4, and CO. We analyzed the aircraft measurements obtained in two campaigns: a within-boundary layer survey over the western Republic of Korea (hereafter Korea) for analyzing the CO2 and CH4 emission characteristics for each season (the climate change monitoring (CM) CM mission), and a low altitude survey over the Yellow Sea for monitoring the pollutant plumes transported into Korea from China (the environment monitoring (EM) mission). This study analyzed CO2, CH4, and CO data from a total of 14 flights during 2019 season. To characterize the regional combustion sources signatures of CO2 and CH4, we calculated the short-term (1-min slope based on one second data) regression slope of CO to CO2 and CH4 to CO enhancements (subtracted with background level, present as ∆CO, ∆CO2, and ∆CH4); slope filtered with correlation coefficients (R2) (&lt;0.4 were ignored). These short-term slope analyses seem to be sensitive to aircraft measurements in which the instrument samples short-time varying mixtures of different air masses. The EM missions all of which were affected by pollutants emitted in China, show the regression slope between ∆CO and ∆CO2 with of 1.8–6% and 0.3–0.7 between ∆CH4 and ∆CO. In particular, the regression slope between ∆CO and ∆CO2 increased to &gt;4% when air flows from east-central China such as Hebei, Shandong, and Jiangsu provinces, etc., sustained for 1–3 days, suggesting pollutants from these regions were most likely characterized by incomplete fossil fuel combustions at the industries. Over 80% of the observations in the Western Korea missions were attributed to Korean emission sources with regression slope between ∆CO and ∆CO2 of 0.5–1.9%. The CO2 emissions hotspots were mainly located in the north-Western Korea of high population density and industrial activities. The higher CH4 were observed during summer season with the increasing concentration of approximately 6% over the background level, it seems to be attributed to biogenic sources such as rice paddies, landfill, livestock, and so on. It is also noted that occurrences of high pollution episodes in North-Western Korea are more closely related to the emissions in China than in Korea.

A two-dimensional analytical model for organic contaminants transport in a transition layer-cutoff wall-aquifer system

Cutoff walls are widely used as in-situ vertical barriers to control pollution plumes migration in aquifer. A two-dimensional analytical model for the transport of organic contaminants through a layered subsurface system with a cutoff wall is developed. The model considers a coupled advection-dispersion-adsorption-degradation process in the whole system and a non-uniform concentration distribution of a contaminant source with respect to depth. The solution was effectively validated against a one-dimensional analytical solution and a two-dimensional numerical solution. The migration behavior of contaminants in the triple-layer system and the service performance of a cutoff wall are investigated. It is demonstrated that the previous one-dimensional contaminant migration solution would underestimate the polluted ranges but overestimate the migration distance. The consideration of a non-uniformly distributed contamination source is of great importance, especially for narrowly contaminated aquifer. The biodegradation in a cutoff wall has a significant influence on the transport of an organic contaminant through the layered system when its half-life in the cutoff wall is less than 5 years, and this effect would be enhanced when the biodegradation in natural soil is also considered. The proposed model is a practical tool for performing a comprehensive design of the location and thickness of a cutoff wall.

Characterizing sources of high surface ozone events in the southwestern US with intensive field measurements and two global models

Abstract. The detection and attribution of high background ozone (O3) events in the southwestern US is challenging but relevant to the effective implementation of the lowered National Ambient Air Quality Standard (NAAQS; 70 ppbv). Here we leverage intensive field measurements from the Fires, Asian, and Stratospheric Transport−Las Vegas Ozone Study (FAST-LVOS) in May–June 2017, alongside high-resolution simulations with two global models (GFDL-AM4 and GEOS-Chem), to study the sources of O3 during high-O3 events. We show possible stratospheric influence on 4 out of the 10 events with daily maximum 8 h average (MDA8) surface O3 above 65 ppbv in the greater Las Vegas region. While O3 produced from regional anthropogenic emissions dominates pollution events in the Las Vegas Valley, stratospheric intrusions can mix with regional pollution to push surface O3 above 70 ppbv. GFDL-AM4 captures the key characteristics of deep stratospheric intrusions consistent with ozonesondes, lidar profiles, and co-located measurements of O3, CO, and water vapor at Angel Peak, whereas GEOS-Chem has difficulty simulating the observed features and underestimates observed O3 by ∼20 ppbv at the surface. On days when observed MDA8 O3 exceeds 65 ppbv and the AM4 stratospheric ozone tracer shows 20–40 ppbv enhancements, GEOS-Chem simulates ∼15 ppbv lower US background O3 than GFDL-AM4. The two models also differ substantially during a wildfire event, with GEOS-Chem estimating ∼15 ppbv greater O3, in better agreement with lidar observations. At the surface, the two models bracket the observed MDA8 O3 values during the wildfire event. Both models capture the large-scale transport of Asian pollution, but neither resolves some fine-scale pollution plumes, as evidenced by aerosol backscatter, aircraft, and satellite measurements. US background O3 estimates from the two models differ by 5 ppbv on average (greater in GFDL-AM4) and up to 15 ppbv episodically. Uncertainties remain in the quantitative attribution of each event. Nevertheless, our multi-model approach tied closely to observational analysis yields some process insights, suggesting that elevated background O3 may pose challenges to achieving a potentially lower NAAQS level (e.g., 65 ppbv) in the southwestern US.

Fenômeno de meandro do vento e a função de autocorrelação calculada com base na concentração de poluentes simulada pelo modelo transiente 3D-GILTT

The aim of this work is to present a pollutants dispersion transient model in low wind conditions to simulate the behavior of the pollutants plume in the atmosphere, considering in the model the u e v horizontal wind components simulated by the LES-PALM model. The dispersion model is based in the advection-diffusion equation and represent by this methodology the wind meandering phenomenon. The Generalized Integral Laplace Transform Technique in three dimensions (3D- GILTT) solves the transient advection-diffusion equation. The data utilized to initialize the simulations are data of the low wind INEL (Idaho National Engineering Laboratory) experiment accomplished in EUA. The results show that the dispersion model reproduces the wind meandering phenomenon, in other words, the autocorrelation function of the concentration simulated over an hour presents the negative lobule, similarly to observed lobules in the u and v wind components. Therefore, the model simulates the pollutants plume in a satisfactory way and can be used to air quality regulatory applications in low wind and wind meandering conditions.

Pyrocumulonimbus Stratospheric Plume Injections Measured by the ACE‐FTS

AbstractThe Atmospheric Chemistry Experiment (ACE) is a satellite‐based mission that probes Earth's atmosphere via solar occultation. The primary instrument on board is a high‐resolution infrared Fourier transform spectrometer (Atmospheric Chemistry Experiment Fourier Transform Spectrometer, ACE‐FTS), providing altitude‐resolved volume mixing ratio measurements for numerous atmospheric constituents, including many biomass burning products. The ACE mission has observed the aftermath of three major pyrocumulonimbus events, in which extreme heat from intense fires created a pathway for directly injecting into the stratosphere plumes of gaseous and aerosol pollutants. These three events were associated with severe Australian bushfires from 2009 and 2019/2020, along with intense North American wildfires from summer 2017. The ACE‐FTS measured stratospheric plumes containing aerosols, enhanced levels of gaseous fire products, and tropospheric air transported into the stratosphere. Infrared spectral features indicate strikingly similar aerosol composition for all three events, characteristic of oxygenated organic matter.

A particle model of ion thruster plume Mo source based on grid erosion

Ion thruster's plume can bring serious contamination to satellite, especially the molybdenum (Mo) charge-exchange (CEX) ions in plume. Therefore, it is critical to describe the emission and movement of Mo atoms appropriately for the prediction of plume pollution. In this paper, a 3D Mo source model is constructed based on grid erosion. In this model, the emission of Mo atom is given by the erosion rate of grid. Then by using a 3D plume particle model and the 3D Mo source model, the Mo CEX ions of LIPS-300 ion thruster is calculated. The influences of the non-uniformity of upstream plasma, the CEX collision, and the Mo atom initial distribution on the Mo CEX ion distribution are considered. The results show that the above aspects have a significant effect on the distribution of Mo CEX ions. The simulation results of Mo CEX ions obtained by this paper's model are also compared with those based on the commonly used empirical hypothesis of Mo atoms. It is shown that the results based on empirical hypothesis are similar to those under the uniform initial distribution of Mo atoms, and the range of Mo CEX ion distribution is increased.

Numerical simulation and prediction of chlorinated hydrocarbon migration in eastern Jinan

In this paper, the pollution of carbon tetrachloride in the Groundwater system is taken as the main research object. By selecting the monitoring sample points of shallow groundwater and using MT3DMS module in GMS numerical simulation software to establish the migration and transformation model of typical chlorinated hydrocarbons. Sequentially, predicting the development trend of carbon tetrachloride pollution. The results show that with the passage of time, the concentration of pollutants decreases due to the adsorption and attenuation of solid phase media, the pollution range of carbon tetrachloride decreases, and the overall pollution degree of carbon tetrachloride in karst water decreases. From the simulation results, the concentration time-duration curves of the typical points in different parts of the southern, central and northern parts of the pollution plume were extracted, and the linear equation was used for fitting. The fitting effect is good and conforms to the first-order attenuation equation, providing ideas for the prevention and treatment of chlorinated hydrocarbon pollution in the subsequent groundwater.

Megacity and local contributions to regional air pollution: an aircraft case study over London

Abstract. In July 2017 three research flights circumnavigating the megacity of London were conducted as a part of the STANCO training school for students and early career researchers organised by EUFAR (European Facility for Airborne Research). Measurements were made from the UK's Facility for Airborne Atmospheric Measurements (FAAM) BAe-146-301 atmospheric research aircraft with the aim to sample, characterise and quantify the impact of megacity outflow pollution on air quality in the surrounding region. Conditions were extremely favourable for airborne measurements, and all three flights were able to observe clear pollution events along the flight path. A small change in wind direction provided sufficiently different air mass origins over the 2 d such that a distinct pollution plume from London, attributable marine emissions and a double-peaked dispersed area of pollution resulting from a combination of local and transported emissions were measured. We were able to analyse the effect of London emissions on air quality in the wider region and the extent to which local sources contribute to pollution events. The background air upwind of London was relatively clean during both days; concentrations of CO were 88–95 ppbv, total (measured) volatile organic compounds (VOCs) were 1.6–1.8 ppbv and NOx was 0.7–0.8 ppbv. Downwind of London, we encountered elevations in all species with CO&gt;100 ppbv, VOCs 2.8–3.8 ppbv, CH4&gt;2080 ppbv and NOx&gt;4 ppbv, and peak concentrations in individual pollution events were higher still. Levels of O3 were inversely correlated with NOx during the first flight, with O3 concentrations of 37 ppbv upwind falling to ∼26 ppbv in the well-defined London plume. Total pollutant fluxes from London were estimated through a vertical plane downwind of the city. Our calculated CO2 fluxes are within the combined uncertainty of those estimated previously, but there was a greater disparity in our estimates of CH4 and CO. On the second day, winds were lighter and downwind O3 concentrations were elevated to ∼39–43 ppbv (from ∼32 to 35 ppbv upwind), reflecting the contribution of more aged pollution to the regional background. Elevations in pollutant concentrations were dispersed over a wider area than the first day, although we also encountered a number of clear transient enhancements from local sources. This series of flights demonstrated that even in a region of megacity outflow, such as the south-east of the UK, local fresh emissions and more distant UK sources of pollution can all contribute substantially to pollution events. In the highly complex atmosphere around a megacity where a high background level of pollution mixes with a variety of local sources at a range of spatial and temporal scales and atmospheric dynamics are further complicated by the urban heat island, the use of pollutant ratios to track and determine the ageing of air masses may not be valid. The individual sources must therefore all be well-characterised and constrained to understand air quality around megacities such as London. Research aircraft offer that capability through targeted sampling of specific sources and longitudinal studies monitoring trends in emission strength and profiles over time.

Lake hydrodynamics intensify the potential impact of watershed pollutants on coastal ecosystem services

Watersheds deliver numerous pollutants to the coastline of oceans and lakes, thereby jeopardizing ecosystem services. Regulatory frameworks for stressors often focus on loading rates without accounting for the physical dynamics of the receiving water body. Here, we use a three-dimensional hydrodynamic model to simulate the transport of a generic tributary-delivered anthropogenic pollutant within Lake Michigan based on the location and timing of loading. Simulating pollutant plumes from 11 rivers, and their intersections with coastal ecosystem services, reveals strong mediation of potential impacts by lake physics. Trapped pollutants accumulate in nearshore waters during spring peak flows, and become diluted by spreading offshore during the summer. The threat to coastal ecosystem services posed by pollutant loading differs sharply among rivers; high potential impact arises from the spatiotemporal coincidence of tributary input rates, lake mixing dynamics, and multiple human uses of the shoreline. Simultaneous pollution from multiple rivers yields overlapping plumes, creating a second way in which lake hydrodynamics can amplify potential impacts on coastal ecosystem services. Our simulations demonstrate that the physical dynamics of large water bodies can create a dynamic stressor landscape arising from multiple independent sources of non-point-source pollution. The design and implementation of pollution regulations rarely account for spatial and temporal complexities of load processing in receiving waters, yet the resulting variability is likely to strongly mediate impacts on society. As hydrodynamic models improve, our analytical framework could be applied to a wide range of pollutants and waterbodies to enhance the sustainable use of coastal ecosystems.

Using MODFLOW/MT3DMS and electrical resistivity tomography to characterize organic pollutant migration in clay soil layer with a shallow water table

ABSTRACT The clay soil in the middle and lower reaches of the Yangtze River in China is widely distributed and the groundwater table is shallow. In order to accurately analyze the distribution and assess the potentially harmful effects of the pollutants in this region, it’s necessary to study the diffusion rate and subsequent concentrations of organic pollutants. Our study area, located in Kunshan in the Jiangsu Province, represents a typical contaminated site consisting of a silty clay layer located in a shallow water table. Our model for the horizontal diffusion, vertical diffusion, and concentration distribution of organic pollutants through this clay layer over 30 years. The simulation results were compared to the measured horizontal distribution of the pollutant concentration at a depth of 2 m and the electrical resistivity tomography data reflecting the longitudinal changes in the polluted area. Our model generated accurate pollutant concentration and diffusion depth results, but the modelled horizontal diffusion distance of the pollution plume did not agree with observational data. After increasing the soil permeability coefficient at a depth of 2 m by a factor of 20,000, the numerical simulation results more closely match those of the measured results. Based on model results, we propose that the seasonal fluctuation of the groundwater table controls the vertical diffusion distance, and that the wide horizontal pollutant diffusion distance is a consequence of the sharp increase in the cohesive soil permeability (caused by repeated water gain and loss).

Evaluation of CMAQ modeling sensitivity to planetary boundary layer parameterizations for gaseous and particulate pollutants over a fjord valley

Abstract Three-dimensional chemical transport models are useful for spatial and temporal analyses of outdoor air quality. However, the suitability of boundary-layer parameterizations for air pollution modeling over deep, coastal valleys has seldom been tested. An evaluation of the Community Multiscale Air Quality (CMAQ) model performance for five planetary boundary-layer schemes (PBL) with the Weather Research and Forecasting (WRF) meteorological driver was conducted at 1-km horizontal resolution for fine particulate matter (PM2.5), sulfur dioxide (SO2) and nitrogen dioxide (NO2) over the Terrace-Kitimat valley of northwestern British Columbia, Canada. The top-ranked schemes were Mellor-Yamada-Nakanishi-Niino Level 3 (MYNN3) for PM2.5 and Mellor-Yamada-Janjic for NO2. Both schemes ranked high for absolute SO2 levels, but the MYJ and Asymmetric Convective Model, version 2 (ACM2) schemes qualitatively emulated peak summertime diurnal concentrations in the near field of elevated point sources. Greater nighttime SO2 concentrations with MYNN3 and Yonsei University PBL schemes, in less agreement with station monitoring 8 km downwind of emissions from tall stacks, suggested sustained pollutant mixing and downward transport within the nocturnal boundary layer. Consequently, for these two schemes with representations of nonlocal mass flux transfers between model layers, inland penetrations of pollutant plumes were farther than those of ACM2, MYJ, and University of Washington schemes. For NO2 and PM2.5 that mainly discharged passively from fugitive, ground-level sources, hence are less accurately quantified than SO2 emissions, the fully local MYJ, and semi-local MYNN3 PBL schemes more reasonably reproduced peak season concentrations than other schemes. It is concluded that for air pollution modeling in rugged, remote areas, the mode of pollutant emissions is important for the choice of a PBL scheme. PM2.5 was consistently underestimated by the various PBL schemes, and aspects for improving CMAQ simulations for a complex environment are discussed.

Ship emission of nitrous acid (HONO) and its impacts on the marine atmospheric oxidation chemistry

Nitrous acid (HONO) is an important reservoir of the hydroxyl radical (OH) and thus plays a central role in tropospheric chemistry. Exhaust from engines has long been known as a major primary source of HONO, yet most previous studies focused on vehicle emissions on land. In comparison, ship emissions of HONO have been rarely characterized, and their impacts on the tropospheric oxidation chemistry have not been quantified. In this study, we conducted cruise measurements of HONO and related species over the East China Sea. Contrasting air masses from pristine marine background air to highly polluted ship plumes were encountered. The emission ratio of ΔHONO/ΔNOx (0.51 ± 0.18%) was derived from a large number of fresh ship plumes. Using the in-situ measured emission ratio, a global ship emission inventory of HONO was developed based on the international shipping emissions of NOx in the Community Emission Data System inventory. The global shipping voyage emits approximately 63.9 ± 22.2 Gg yr−1 of HONO to the atmosphere. GEOS-Chem modelling with the addition of ship-emitted HONO showed that HONO concentrations could increase up to 40–100% over the navigation areas, leading to about 5–15% increases of primary OH production in the early-morning time. This study elucidates the potentially considerable effects of ship HONO emissions on the marine atmospheric chemistry, and calls for further studies to better characterize the ship emissions of HONO and other reactive species, which should be taken into account by global and regional models.

Tracing multiple sources of groundwater pollution in a complex carbonate aquifer (Tarnowskie Góry, southern Poland) using hydrogeochemical tracers, TCE, PCE, SF6 and CFCs

A comprehensive study on the sources of groundwater contamination in the Triassic carbonate aquifer, southern Poland, was conducted. The Gliwice aquifer is an important source of potable water in the Silesia region, the most industrialized part of Poland. Groundwater quality has been deteriorating over the last decades, which encouraged researchers to undertake comprehensive study to identify the sources and fates of the observed pollution. The presented study comprised analyses of major and minor ions, trichloroethylene (TCE) and tetrachloroethylene (PCE), CFC-11, CFC-12, SF6, Ne and Ar in groundwater. The results showed that shallow groundwater within the Tarnowskie Góry town, located in the recharge zone of the aquifer, was more contaminated than groundwater abstracted from deeper part of the aquifer within the town, as well as groundwater located downgradient. A contamination plume of boron indicated an impact of the closed chemical plant, operating in the 20th century. Groundwater in the vicinity of the chemical plant was significantly altered, which was manifested by elevated concentrations of Cl−, SO42-, Na+, total Fe and Mn. The study revealed groundwater contamination with CFC-11 and CFC-12. Comparison of concentrations obtained in two field campaigns (in 2010 and 2015) showed an increase in the extent of pollution plumes. The third analysed gaseous tracer, SF6, did not appear to come from non-atmospheric sources, therefore, it was possible to calculate groundwater age using lumped parameter models. The results showed relatively young ages of the analysed groundwater samples, from 4 to 5 to 30–50 years. The youngest groundwater were found close to the Drama River, suggesting infiltration of the surface water into the carbonate aquifer. This feature of the river was confirmed by the observation of TCE and PCE concentrations in groundwater. Central part of the Tarnowskie Góry town was a source area for TCE and PCE contamination. Two directions of pollutants migration were observed, one of them was induced by the drainage of the historic ore mine and subsequently the Drama River – recipient of water coming from the mine drainage.

Overview of aerosol optical properties over southern West Africa from DACCIWA aircraft measurements

Abstract. Southern West Africa (SWA) is an African pollution hotspot but a relatively poorly sampled region of the world. We present an overview of in situ aerosol optical measurements collected over SWA in June and July 2016 as part as of the DACCIWA (Dynamics-Aerosol-Chemistry-Clouds Interactions in West Africa) airborne campaign. The aircraft sampled a wide range of air masses, including anthropogenic pollution plumes emitted from the coastal cities, long-range transported biomass burning plumes from central and southern Africa and dust plumes from the Sahara and Sahel region, as well as mixtures of these plumes. The specific objective of this work is to characterize the regional variability of the vertical distribution of aerosol particles and their spectral optical properties (single scattering albedo: SSA, asymmetry parameter, extinction mass efficiency, scattering Ångström exponent and absorption Ångström exponent: AAE). The first findings indicate that aerosol optical properties in the planetary boundary layer were dominated by a widespread and persistent biomass burning loading from the Southern Hemisphere. Despite a strong increase in aerosol number concentration in air masses downwind of urban conglomerations, spectral SSA were comparable to the background and showed signatures of the absorption characteristics of biomass burning aerosols. In the free troposphere, moderately to strongly absorbing aerosol layers, dominated by either dust or biomass burning particles, occurred occasionally. In aerosol layers dominated by mineral dust particles, SSA varied from 0.81 to 0.92 at 550 nm depending on the variable proportion of anthropogenic pollution particles externally mixed with the dust. For the layers dominated by biomass burning particles, aerosol particles were significantly more light absorbing than those previously measured in other areas (e.g. Amazonia, North America), with SSA ranging from 0.71 to 0.77 at 550 nm. The variability of SSA was mainly controlled by variations in aerosol composition rather than in aerosol size distribution. Correspondingly, values of AAE ranged from 0.9 to 1.1, suggesting that lens-coated black carbon particles were the dominant absorber in the visible range for these biomass burning aerosols. Comparison with the literature shows a consistent picture of increasing absorption enhancement of biomass burning aerosol from emission to remote location and underscores that the evolution of SSA occurred a long time after emission. The results presented here build a fundamental basis of knowledge about the aerosol optical properties observed over SWA during the monsoon season and can be used in climate modelling studies and satellite retrievals. In particular and regarding the very high absorbing properties of biomass burning aerosols over SWA, our findings suggest that considering the effect of internal mixing on absorption properties of black carbon particles in climate models should help better assess the direct and semi-direct radiative effects of biomass burning particles.

Optimal design of groundwater pollution monitoring network based on the SVR surrogate model under uncertainty.

The simulation-optimization method is widely used in the design of the groundwater pollution monitoring network (GPMN). The uncertainty of the simulation model will significantly affect the design results of GPMN. When the Monte Carlo method is used to consider the influence of model uncertainty on the optimization results, the simulation model needs to be invoked many times, which will cause a huge amount of calculation. To reduce the calculation load, the study proposed to use the support vector regression (SVR) method to construct the surrogate model to couple the simulation model and the optimization model in the optimal design of GPMN. The optimization goal is to maximize the accuracy of the spatial description of pollution plume in each monitoring period. The study also considered the dynamic changes in the migration and morphological of pollution plumes in the optimization of GPMN. Finally, the West Shechang coal gangue pile in Fushun of China was used as a case study to verify the effectiveness of the above method. The results demonstrate that the SVR surrogate model can fit the input-output relationship of the simulation model to a high degree with less computation. The optimized monitoring network can reveal essential and comprehensive information about pollution plumes. The study provides a stable and reliable method for the design of GPMN.

Simulation of pollutants spreading from a sewage outfall in the Rijeka Bay

Results from a 3D numerical simulation of wind-induced currents and pollution spreading from a sewage outfall are described.The goal was to predict seawater sanitary quality in the Rijeka Bay, Adriatic Sea. A sea motion model was coupled with a modelof transport and chemical reactions of fecal coliforms (FC), fecal streptococci (FS) and dissolved oxygen. The selected simulationperiod of 36 hours following wastewater discharge was found to be sufficient for a significant extinction of bacteria. The simulationwas carried out for eight wind directions and two intensities (moderate and high). Mesh convergence was obtained. Twomesh sizes were coupled: coarse, for the whole Bay, and fine, for the northern part of the Bay, close to the sewage discharge ofthe Rijeka city.For all considered wind directions, the pollution plume with a concentration higher than 100 FC and 100 FS per 100 ml of seawateris conveyed mostly parallel to the coast in either north-west or south-east directions. The plume does not rise to the surfacebut stays at the depth of 10 to 20 meters. This is a consequence of the hydrodynamics of the Rijeka Bay: the bora wind carriesthe surface water layer out of the Bay through the Middle and Great Gates, while cold water enters the Bay from the layer belowthe thermocline. During the southern wind (jugo), the situation is reversed: warmer surface water enters the Bay through eitherthe Middle Gate or the Great Gate, while cold seawater exits through the bottom layer, accumulating warmer seawater in the Bay.The conclusion is that the Rijeka city sewage discharge Delta is well-designed, and the microorganism concentration is wellwithin the suggested regulatory range. The discharge site is far enough from the coast, where local streamlines are mostly parallelto the coast, hence the elevated pollution concentration does not come close to swimming and recreational areas. Even if thedischarge increases by 50%, which is unlikely in the near future, the pollution at beaches will stay within regulatory boundaries.

Virtual experiments to assess opportunities and pitfalls of CSIA in physical-chemical heterogeneous aquifers

Degradation of chlorinated ethenes (CEs) in low conductivity layers of aquifers reduces pollution plume tailing and accelerates natural attenuation timeframes. The degradation pathways involved are often different from those in the higher conductive layers and might go undetected when only highly conductive layers are targeted in site assessments. Reactive transport model simulations (PHT3D in FloPy) were executed to assess the performance of dual carbon and chlorine compound specific stable isotope analysis (CSIA) in degradation pathway identification and quantification in a coupled physical-chemical heterogeneous virtual aquifer. Degradation rate constants were assumed correlated to the hydraulic conductivity: positively for oxidative transformation (higher oxygen availability in coarser sands) and negatively for chemical reduction (higher content of reducing solids in finer sediments). Predicted carbon isotope ratios were highly heterogeneous. They generally increased downgradient of the pollution source but the large variation across depth illustrates that monotonously increasing isotope ratios downgradient, as were associated with the oxidative component, are not necessarily a common situation when degradation is favorable in low conductivity layers. Dual carbon-chlorine CSIA performed well in assessing the occurrence of the spatially separated degradation pathways and the overall degradation, provided appropriate enrichment factors were known and sufficiently different. However, pumping to obtain groundwater samples especially from longer well screens causes a bias towards overestimation of the contribution of oxidative transformation associated with the higher conductive zones. As degradation was less intense in these highly conductive zones under the simulated conditions, overall degradation was underestimated. In contrast, in the usual case of limited CSIA data, dual CSIA plots may rather indicate dominance of chemical reduction, while oxidative transformation could go unnoticed, despite being an equally important degradation pathway.