Source-receptor Relationships Research Articles

Future year ozone source attribution modeling study using CMAQ-ISAM

ABSTRACTTo achieve the current United States National Ambient Air Quality Standards (NAAQS) attainment level for ozone or particulate matter, current photochemical air quality models include tools to determine source apportionment and/or source sensitivity. Previous studies by the authors have used the Ozone and Particulate Matter Source Apportionment Technology and Higher-order Decoupled Direct Method probing tools in CAMx to investigate these source-receptor relationships for ozone. The recently available source apportionment for CMAQ, referred to as the Integrated Source Apportionment Method (ISAM), was used in this study to conduct future year (2030) source attribution modeling. The CMAQ-ISAM ozone source attribution results for selected cities across the U.S. showed boundary conditions were the dominant contributor to the future year highest July maximum daily 8-hour average (MDA8) ozone concentrations. Point sources were generally larger contributors in the eastern U.S. than in the western U.S. The contributions of on-road mobile emissions were around 5 ppb at most of the cities selected for analysis. Off-road mobile source contributions were around 20 ppb or nearly 30%. Since boundary conditions play an important role in future year ozone levels, it is important to characterize future year boundary conditions accurately. The current implementation of ISAM in CMAQ 5.0.2 requires significant computing resources for ozone source attribution, making it difficult to conduct long-term simulations for large domains. The computing requirements for PM source attribution are even more onerous. CMAQ 5.2 was released after this study was completed, and does not include ISAM. If an efficient version of ISAM becomes available, it could be used in long-term ozone and PM2.5 studies. Implications: Ozone source attribution results provide useful information on important emission source contribution categories and provide some initial guidance on future emission reduction strategies. This study explains a new source apportionment technique, CMAQ-ISAM, and compares it to CAMx OSAT. The techniques have similar results: ozone’s highest source contributor is boundary conditions, followed by point sources, then off-road mobile sources. The current version of ISAM in CMAQ 5.0.2 requires significant computing resources for ozone source attribution, while the computing requirements for PM source attribution are even more onerous. CMAQ 5.2 was released after this study was completed, and does not include ISAM.

Global-scale atmospheric modeling of aerosols to assess metal source-receptor relationships for life cycle assessment

Metals have often been identified as the main contributors to (eco)toxicological impacts in life cycle assessment (LCA) studies. Indeed, environmental fate models are generally unsuitable for these substances as they were developed for organics. Recent work has focused on improving these models by accounting for biogeochemical conditions (e.g., pH, redox potential, organic matter, etc.). These conditions often dictate metal bioavailability and (eco)toxicity. However, biogeochemical conditions cannot be integrated into an LCA framework due to a lack of high-resolution spatially differentiated factors describing the metal atmospheric pathway. This paper aims to derive worldwide source-receptor relationships for aerosol particles to ascertain the atmospheric mechanisms (i.e., dispersion, transport, and deposition) of metals (i.e., copper, cadmium, lead, nickel, chromium, and zinc) at a relatively high resolution. We compared black carbon, sulfate, and nitrate aerosols according to the framework developed by Roy et al. Atmos Environ 62:74–81, (2012), which requires the results of a year-long (2005) GEOS-Chem (a three-dimensional global-scale tropospheric model) simulation. These aerosols are used as proxies since metals may sorb with them for short- and long-range transport. Source-receptor matrices (SRMs), whose elements are fate factors, were calculated at a global 2° × 2.5° resolution. The atmospheric fate of metals, as described by black carbon and sulfate aerosols, is similar while the atmospheric fate of nitrate is significantly different: 70% of the black carbon or sulfate emissions deposits within in a radius of less than 2000 km while this percentage drops to 40% with nitrate. Nitrate aerosol also showed the lowest agreement with EMEP modeling. Nitrate should not be considered as the optimal proxy. A case can be made for either sulfate or black carbon as proxies for metal; the latter is recommended as it showed the best agreement with EMEP modeling at the source location and similar agreement in the mid/long-range transport. The SRMs outlined in this paper facilitate further modeling developments without having to run the underlying tropospheric model, thus paving the way for the assessment of the regional life cycle inventories of a global economy.

Glyphosate and atrazine in rainfall and soils in agroproductive areas of the pampas region in Argentina

The presence in the atmosphere of glyphosate (GLP) and atrazine (ATZ) was investigated—those pesticides dominating the market in Argentina—through rain, as the main climatic phenomenon associated with wet deposition, both through analyzing source-receptor relationships with soil along with the climatic influences that may condition that transport and through estimating the annual deposition on the surface of the Argentine pampas. Rainwater samples (n = 112) were collected throughout each rainfall in urban areas of the pampas having different degrees of land use and with extensive crop production plus subsurface-soil samples (n = 58) from the relevant periurban sites. The herbicides—analyzed by liquid-chromatography–mass-spectrometry—were detected in >80% of the rain samples at median-to-maximum concentrations of 1.24–67.3 μg·L−1 (GLP) and 0.22–26.9 μg·L−1(ATZ), while aminomethylphosphonic acid (AMPA) was detected at 34% (0.75–7.91 μg·L−1). In soils, GLP was more frequently registered (41%; 102–323 μg·kg−1) followed by ATZ (32%; 7–66 μg·kg−1) and then AMPA (22%; 223–732 μg·kg−1). The maximum GLP concentrations quantified in rainwater exceeded the previously reported levels for the USA and Canada. No associations were observed between soil and rainwater concentrations in the same monitoring areas—despite the soil's action as a source, as evidenced through the AMPA present in rainwater. Median GLP concentrations were significantly associated with isohyets, in an increasing gradient from the east to the west—as such in an inverse pattern to that of the annual rainfall volumes; whereas ATZ-rainwater levels exhibited no characteristic spatial configuration. The estimated annual deposition of GLP by rainfall indicated that more than onc source of a herbicide can lead to its presence in the atmosphere and points out the relevance of rainfall's contribution to the surface levels of a pollutant.

TOAST 1.0: Tropospheric Ozone Attribution of Sources with Tagging for CESM 1.2.2

Abstract. A system for source attribution of tropospheric ozone produced from both NOx and volatile organic compound (VOC) precursors is described, along with its implementation in the Community Earth System Model (CESM) version 1.2.2 using CAM4. The user can specify an arbitrary number of tag identities for each NOx or VOC species in the model, and the tagging system rewrites the model chemical mechanism and source code to incorporate tagged tracers and reactions representing these tagged species, as well as ozone produced in the stratosphere. If the user supplies emission files for the corresponding tagged tracers, the model will produce tagged ozone tracers which represent the contribution of each of the tag identities to the modelled total tropospheric ozone. Our tagged tracers preserve Ox. The size of the tagged chemical mechanism scales linearly with the number of specified tag identities. Separate simulations are required for NOx and VOC tagging, which avoids the sharing of tag identities between NOx and VOC species. Results are presented and evaluated for both NOx and VOC source attribution. We show that northern hemispheric surface ozone is dominated year-round by anthropogenic emissions of NOx, but that the mix of corresponding VOC precursors changes over the course of the year; anthropogenic VOC emissions contribute significantly to surface ozone in winter–spring, while biogenic VOCs are more important in summer. The system described here can provide important diagnostic information about modelled ozone production, and could be used to construct source–receptor relationships for tropospheric ozone.

The impact of future emission policies on tropospheric ozone using a parameterised approach

Abstract. This study quantifies future changes in tropospheric ozone (O3) using a simple parameterisation of source–receptor relationships based on simulations from a range of models participating in the Task Force on Hemispheric Transport of Air Pollutants (TF-HTAP) experiments. Surface and tropospheric O3 changes are calculated globally and across 16 regions from perturbations in precursor emissions (NOx, CO, volatile organic compounds – VOCs) and methane (CH4) abundance only, neglecting any impact from climate change. A source attribution is provided for each source region along with an estimate of uncertainty based on the spread of the results from the models. Tests against model simulations using the Hadley Centre Global Environment Model version 2 – Earth system configuration (HadGEM2-ES) confirm that the approaches used within the parameterisation perform well for most regions. The O3 response to changes in CH4 abundance is slightly larger in the TF-HTAP Phase 2 than in the TF-HTAP Phase 1 assessment (2010) and provides further evidence that controlling CH4 is important for limiting future O3 concentrations. Different treatments of chemistry and meteorology in models remain one of the largest uncertainties in calculating the O3 response to perturbations in CH4 abundance and precursor emissions, particularly over the Middle East and south Asia regions. Emission changes for the future Evaluating the CLimate and Air Quality ImPacts of Short-livEd Pollutants (ECLIPSE) scenarios and a subset of preliminary Shared Socioeconomic Pathways (SSPs) indicate that surface O3 concentrations will increase regionally by 1 to 8 ppbv in 2050. Source attribution analysis highlights the growing importance of CH4 in the future under current legislation. A change in the global tropospheric O3 radiative forcing of +0.07 W m−2 from 2010 to 2050 is predicted using the ECLIPSE scenarios and SSPs, based solely on changes in CH4 abundance and tropospheric O3 precursor emissions and neglecting any influence of climate change. Current legislation is shown to be inadequate in limiting the future degradation of surface ozone air quality and enhancement of near-term climate warming. More stringent future emission controls provide a large reduction in both surface O3 concentrations and O3 radiative forcing. The parameterisation provides a simple tool to highlight the different impacts and associated uncertainties of local and hemispheric emission control strategies on both surface air quality and the near-term climate forcing by tropospheric O3.

Satellite- and ground-based measurements of CO2 over the Indian region: its seasonal dependencies, spatial variability, and model estimates

ABSTRACTThe present study demonstrates the distribution of carbon dioxide (CO2) concentration over the Indian region and the surrounding oceanic regions during 2009–2012, using measurements from satellites viz., Greenhouse Gases Observing Satellite (GOSAT) and Atmospheric Infrared Sounder, Carbon Tracker (CT) model simulations and flask measurements from two Indian stations Sinhagad (SNG) (73°45′ E, 18°21′36″ N) and Cape Rama (CRI) (73°54′ E, 15°6′ N). The concentration of CO2 is observed to be maximum during pre-monsoon and shows a decreasing phase during the post-monsoon season. In a regional scale, it is found that Indo-Gangetic Plain and northern India have relatively higher concentrations compared to the other regions. The probability distribution of the concentration differences shows that for most of the time, the differences lie between ±3 ppmv between GOSAT and CT. The comparison between the CO2 flask measurements over SNG and CRI with respect to that of GOSAT and CT clearly reveals that the differences in CO2 are as high as 10 ppmv between the ground- and satellite-based measurements. Further, we utilized the Lagrangian model FLEXible PARTicle (FLEXPART) to understand the source‒receptor relationship over CRI, SNG, and over the equatorial Indian Ocean (IO). The source contributions from the northern and eastern continental regions of the Indian region are found to be more influential over SNG compared to CRI. It is also found from simulations that the equatorial IO has less influence from the continental source and therefore has a reduced seasonal variability compared to the other regions considered in the present study.

A Lagrangian analysis of the moisture budget over the Fertile Crescent during two intense drought episodes

The Fertile Crescent (FC) region comprises the east coast of the Mediterranean Sea and the northern part of the Arabian Peninsula. The FC suffered two severe drought episodes separated by a 7-year period, in 1998–2000 and 2007–2009, which are considered the most severe episodes to hit the region in the last 50 years. A Lagrangian model (FLEXPART) and ERA-Interim data (with a 1° × 1° lat-long resolution) were used to identify for the first time the climatological sources of moisture for the FC and their characteristics. Variability and the source-receptor relationships, concerning their contribution to the precipitation, and the implications regarding the transport of moisture changes over the FC, during the wet season (October-May) from 1980 to 2014 were analysed. The main climatological moisture sources during this period were determined to be the FC itself, the eastern Mediterranean Sea, the Red Sea, the Persian Gulf, the Arabian Sea, the Caspian and Black Seas, and the central and western parts of the Mediterranean Sea.The analysis showed higher anomalous conditions in the moisture transport from some moisture sources during the two outstanding drought episodes. The key feature of the wet seasons during these episodes was a deficit in the moisture losses over the studied area related to the FC itself, the Red and Arabian Seas sources, followed and to a lesser extent by the eastern Mediterranean Sea over the northern part of the FC region. Nevertheless, the moisture supply deficit from the sources was much greater during the 2007–2009 drought event. The SPEI index at large scales (24 months) showed that the 2007–2009 episode was part of longer-term drought conditions that had been developing over the previous months, reinforcing the drought severity given recycling processes attributed to the FC. During the two extreme drought episodes, the mountainous terrain over the northern and eastern FC suffered the highest precipitation deficits, and these areas are, precisely, the most influenced by two of the major moisture sources, namely, the FC and eastern Mediterranean Sea. The decreased moisture contribution from these main sources led to more intense droughts over the region. As a result, both regions should be considered as hotspots to signal severe or extreme droughts in the region.

Seasonal variation, phase distribution, and source identification of atmospheric polycyclic aromatic hydrocarbons at a semi-rural site in Ulsan, South Korea.

Polycyclic aromatic hydrocarbons (PAHs) in gaseous and particulate phases (n = 188) were collected in Ulsan, South Korea, over a period of one year (June 2013‒May 2014) to understand the seasonal variation and phase distribution of PAHs as well as to identify the seasonal PAH emission sources. The target compounds were the 16 US-EPA priority PAHs, with the exception of naphthalene, acenaphthylene, and acenaphthene. Winter and spring had the highest and lowest PAH concentrations, respectively. The mean of the Σ13 PAHs in the gaseous phase (4.11 ng/m3) was higher than that in the particulate phase (2.55 ng/m3). Fractions of the gaseous or 3- and 4-ring PAHs (i.e., Flu, Phe, and Ant) were high in summer, and those of the particulate or 5- and 6-ring PAHs (i.e., BkF, BaP, Ind, DahA, and BghiP) increased in winter. Gas/particle partitioning models also demonstrated the increased contributions of the particulate PAHs in spring and winter. Source identification of PAHs was undertaken using diagnostic ratios, principal component analysis, and positive matrix factorization. The results indicated that pyrogenic sources (e.g., coal combustion) were dominant in winter. Other types of pyrogenic (e.g., industrial fuel combustion) and petrogenic sources were the main PAH sources in summer and autumn. The influence of both sources, especially in summer, might be due to seasonal winds transporting PAHs from the industrial areas. Two types of pyrogenic sources, diesel and coal combustion, were identified as the main PAH sources in spring. This study clearly demonstrates a source-receptor relation of PAHs at a semi-rural site in a heavily industrialized city.

Bayesian source term estimation of atmospheric releases in urban areas using LES approach

The estimation of source information from limited measurements of a sensor network is a challenging inverse problem, which can be viewed as an assimilation process of the observed concentration data and the predicted concentration data. When dealing with releases in built-up areas, the predicted data are generally obtained by the Reynolds-averaged Navier-Stokes (RANS) equations, which yields building-resolving results; however, RANS-based models are outperformed by large-eddy simulation (LES) in the predictions of both airflow and dispersion. Therefore, it is important to explore the possibility of improving the estimation of the source parameters by using the LES approach. In this paper, a novel source term estimation method is proposed based on LES approach using Bayesian inference. The source-receptor relationship is obtained by solving the adjoint equations constructed using the time-averaged flow field simulated by the LES approach based on the gradient diffusion hypothesis. A wind tunnel experiment with a constant point source downwind of a single building model is used to evaluate the performance of the proposed method, which is compared with that of the existing method using a RANS model. The results show that the proposed method reduces the errors of source location and releasing strength by 77% and 28%, respectively.

Source–receptor matrix calculation for deposited mass with the Lagrangian particle dispersion model FLEXPART v10.2 in backward mode

Abstract. Existing Lagrangian particle dispersion models are capable of establishing source–receptor relationships by running either forward or backward in time. For receptor-oriented studies such as interpretation of "point" measurement data, backward simulations can be computationally more efficient by several orders of magnitude. However, to date, the backward modelling capabilities have been limited to atmospheric concentrations or mixing ratios. In this paper, we extend the backward modelling technique to substances deposited at the Earth's surface by wet scavenging and dry deposition. This facilitates efficient calculation of emission sensitivities for deposition quantities at individual sites, which opens new application fields such as the comprehensive analysis of measured deposition quantities, or of deposition recorded in snow samples or ice cores. This could also include inverse modelling of emission sources based on such measurements. We have tested the new scheme as implemented in the Lagrangian particle dispersion model FLEXPART v10.2 by comparing results from forward and backward calculations. We also present an example application for black carbon concentrations recorded in Arctic snow.

Estimating Uncertainty in Global Mercury Emission Source and Deposition Receptor Relationships

Establishing mercury (Hg) source-receptor (SR) relationship matrices provides a tool to improve the understanding of the geographic relationship between regions of Hg release and its eventual deposition. SR relationship matrices are therefore a useful starting point for the development of policies aimed at reducing the impact of Hg emissions from anthropogenic activities (Hganthr) on sensitive ecosystems and areas potentially at risk of Hg contamination. A global Chemical Transport Model (CTM) has been used to simulate the emission, transport and fate of Hganthr from 12 source regions, considering a range of uncertainty in the modelled chemical and physical processes. This ensemble of simulations gives an estimate of the Hg deposition which derives from each source region, as well as an estimate of the uncertainty of the calculated deposition flux. The uncertainty has been calculated using the bootstrap method to estimate this uncertainty in terms of the normalised confidence interval amplitude of the mean (NCIAM). Within the calculated confidence ranges, for almost all regions the contribution to the Hg deposition flux from remote sources is greater than that from domestic sources. Europe and South Asia, where the contributions are statistically indistinguishable, are exceptions, as is East Asia, with local sources dominating the Hg deposition flux. East Asia is the single most important remote source region for most receptor regions. The results yield such high uncertainties in the deposition flux for many receptor regions that the results are unlikely to be taken into consideration by policy makers. This uncertainty is particularly relevant when considering the “domestic” contribution to regional deposition, highlighting the need for more studies to resolve remaining uncertainties in the atmospheric Hg cycle, and Hganthr emission inventories.

Physicochemical factors and their potential sources inferred from long-term rainfall measurements at an urban and a remote rural site in tropical areas

Air pollution can be detected through rainwater composition. In this study, long-term measurements (2000–2014) of wet deposition were made to evaluate the physicochemical interaction and the potential sources of pollution due to changes of land use. The rainwater samples were obtained from an urban site in Kuala Lumpur and a highland-rural site in the middle of Peninsular Malaysia. The compositions of rainwater were obtained from the Malaysian Meteorological Department. The results showed that the urban site experienced more acidity in rainwater (avg=277mm, range of 13.8 to 841mm; pH=4.37) than the rural background site (avg=245mm, range of 2.90 to 598mm; pH=4.97) due to higher anthropogenic input of acid precursors. The enrichment factor (EF) analysis showed that at both sites, SO42−, Ca2+ and K+ were less sensitive to seawater but were greatly influenced by soil dust. NH4+ and Ca2+ can neutralise a larger fraction of the available acid ions in the rainwater at the urban and rural background sites. However, acidifying potential was dominant at urban site compared to rural site. Source-receptor relationship via positive matrix factorisation (PMF 5.0) revealed four similar major sources at both sites with a large variation of the contribution proportions. For urban, the major sources influence on the rainwater chemistry were in the order of secondary nitrates and sulfates>ammonium-rich/agricultural farming>soil components>marine sea salt and biomass burning, while at the background site the order was secondary nitrates and sulfates>marine sea salt and biomass burning=soil components>ammonia-rich/agricultural farming. The long-term trend showed that anthropogenic activities and land use changes have greatly altered the rainwater compositions in the urban environment while the seasonality strongly affected the contribution of sources in the background environment.

Historical and future trends in global source-receptor relationships of mercury

Growing concern about the risk associated with increasing environmental mercury (Hg) concentrations has resulted in a focus on the relationships between intercontinental emitted and accumulated Hg. We use a global biogeochemical Hg model with 8 continental regions and a global ocean to evaluate the legacy impacts of historical anthropogenic releases (2000BCE to 2008AD) on global source-receptor relationships of Hg. Legacy impacts of historical anthropogenic releases are confirmed to be significant on the source-receptor relationships according to our results. Historical anthropogenic releases from Asia account for 8% of total soil Hg in North America, which is smaller than the proportion (~17%) from previous studies. The largest contributors to the global oceanic Hg are historical anthropogenic releases from North America (26%), Asia (16%), Europe (14%) and South America (14%). Although anthropogenic releases from Asia have exceeded North America since the 1970s, source contributions to global Hg receptors from Asia have not exceeded North America so far. Future projections indicate that if Hg emissions are not effectively controlled, Asia will exceed North America as the largest contributor to the global ocean in 2019 and this has a long-term adverse impact on the future environment. For the Arctic Ocean, historical anthropogenic release from North America contributes most to the oceanic Hg reservoir and future projections reveal that the legacy impacts of historical releases from mid-latitudes would lead to the potential of rising Hg in the Arctic Ocean in the future decades, which calls for more effective Hg controls on mid-latitude releases.

Global source attribution of sulfate concentration and direct and indirect radiative forcing

Abstract. The global source–receptor relationships of sulfate concentrations, and direct and indirect radiative forcing (DRF and IRF) from 16 regions/sectors for years 2010–2014 are examined in this study through utilizing a sulfur source-tagging capability implemented in the Community Earth System Model (CESM) with winds nudged to reanalysis data. Sulfate concentrations are mostly contributed by local emissions in regions with high emissions, while over regions with relatively low SO2 emissions, the near-surface sulfate concentrations are primarily attributed to non-local sources from long-range transport. Regional source efficiencies of sulfate concentrations are higher over regions with dry atmospheric conditions and less export, suggesting that lifetime of aerosols, together with regional export, is important in determining regional air quality. The simulated global total sulfate DRF is −0.42 W m−2, with −0.31 W m−2 contributed by anthropogenic sulfate and −0.11 W m−2 contributed by natural sulfate, relative to a state with no sulfur emissions. In the Southern Hemisphere tropics, dimethyl sulfide (DMS) contributes 17–84 % to the total DRF. East Asia has the largest contribution of 20–30 % over the Northern Hemisphere mid- and high latitudes. A 20 % perturbation of sulfate and its precursor emissions gives a sulfate incremental IRF of −0.44 W m−2. DMS has the largest contribution, explaining −0.23 W m−2 of the global sulfate incremental IRF. Incremental IRF over regions in the Southern Hemisphere with low background aerosols is more sensitive to emission perturbation than that over the polluted Northern Hemisphere.

Source-Receptor Relationship Analysis of the Atmospheric Deposition of PAHs Subject to Long-Range Transport in Northeast Asia.

The source-receptor relationship analysis of PAH deposition in Northeast Asia was investigated using an Eulerian regional-scale aerosol chemical transport model. Dry deposition (DD) of PAH was controlled by wind flow patterns, whereas wet deposition (WD) depended on precipitation in addition to wind flow patterns. The contribution of WD was approximately 50-90% of the total deposition, except during winter in Northern China (NCHN) and Eastern Russia (ERUS) because of the low amount of precipitation. The amount of PAH deposition showed clear seasonal variation and was high in winter and low in summer in downwind (South Korea, Japan) and oceanic-receptor regions. In the downwind region, the contributions from NCHN (WD 28-52%; DD 54-55%) and Central China (CCHN) (WD 43-65%; DD 33-38%) were large in winter, whereas self-contributions (WD 20-51%; DD 79-81%) were relatively high in summer. In the oceanic-receptor region, the deposition amount decreased with distance from the Asian continent. The amount of DD was strongly influenced by emissions from neighboring domains. The contributions of WD from NCHN (16-20%) and CCHN (28-35%) were large. The large contributions from China in summer to the downwind region were linked to vertical transport of PAHs over the Asian continent associated with convection.

Inhalation intake fraction of particulate matter from localized indoor emissions

Elevated exposure to airborne particulate matter is linked to deleterious health and well-being outcomes. Exposure assessment can be improved through enhanced understanding of source-receptor relationships, for example as expressed in the inhalation intake fraction metric. This study provides new knowledge about how inhalation intake of airborne particles varies with spatially varying indoor emissions. In a controlled environmental chamber with low background particle levels, we monitored the time- and size-resolved particle concentrations at multiple locations including the subject's breathing zone. We investigated two types of particle emissions: (i) controlled releases from several specific indoor locations; and (ii) natural release from skin and clothing for a range of simulated occupant activities. Findings show that particles released proximate to the human envelope caused a total inhalation intake fraction of 7–10 per thousand, which was 1.5–16 × higher than the intake fraction for other indoor release locations. These outcomes reflect the influence of emissions-receptor proximity combined with the efficient transport of particles by means of the thermal plume to the breathing zone. The results show that the well-mixed representation of an indoor environment could underestimate the inhalation intake by 40–90% for various localized indoor emissions, and by up to 3 × for particles emitted from the human envelope. The post-release exposure period contributed substantially to total inhalation intake. For particles released naturally from the human envelope, inhalation intake fractions varied with activity type and were higher for a subject when seated rather than walking.

Attribution of PM2.5 exposure in Beijing–Tianjin–Hebei region to emissions: implication to control strategies

The Beijing–Tianjin–Hebei (BTH) region is one of the most heavily polluted regions in China, with both high PM2.5 concentrations and a high population density. A quantitative source-receptor relationship can provide valuable insights that can inform effective emission control strategies. Both source apportionment (SA) and source sensitivity (SS) can provide such information from different perspectives. In this study, both methods are applied in northern China to identify the most significant emission categories and source regions for PM2.5 exposure in BTH in 2013. Despite their differences, both models show similar distribution patterns for population and simulated PM2.5 concentrations, resulting in overall high PM2.5 exposure values (approximately 110μg/m3) and particularly high exposure values during the winter (approximately 200μg/m3). Both methods show that local emissions play a dominant role (70%), with some contribution from surrounding provinces (e.g., Shandong) via regional transport. The two methods also agree on the priority of local emission controls: both identify industrial, residential, and agricultural emissions as the top three categories that should be controlled locally. In addition, the effect of controlling agricultural ammonia emissions is approximately doubled when the co-benefits of reducing nitrate are considered. The synthesis of SA and SS for addressing specific categories of emissions provides a quantitative basis for the development of emission control strategies and policies for controlling PM2.5 in China.

Bayesian identification of a single tracer source in an urban-like environment using a deterministic approach

This paper presents a two-step deterministic approach for identifying an unknown point source with a constant emission rate in built-up urban areas. The analytic form of the marginal posterior probability density function of the source location is derived to estimate the source location. The emission rate is then estimated using the conditional posterior distribution. Such a procedure deconstructs the calculation of the joint posterior distribution of the source parameters into calculations of two separate distributions and can thus be easily calculated directly and accurately without stochastic sampling. The proposed method is tested using real data obtained in two wind tunnel scenarios of contaminant dispersion in typical urban geometries represented by block arrays. Computational fluid dynamics (CFD) modeling and the adjoint equations are used to calculate the building-resolving source-receptor relationship required in the identification. The estimated source parameters in both cases are close to true values. In both cases, the source locations are identified with errors less than half of the block size, and the emission rates are well estimated, with only slight overestimation. Moreover, in this paper, we test two potential performance indicators for a posteriori evaluation of the credibility of a certain estimation. One indicator is the size of the highest probability density region, and the other is the angle between the observed and predicted concentration vectors, which is derived from the analytic form of the marginal posterior distribution of the source location. Synthetic concentration data are generated to test the validity of both indicators. It is found that the former is not appropriate for denoting the credibility of estimations but that the latter shows a strong correlation with estimation performance and is likely to be an effective performance indicator for Bayesian source term estimation.

Source-receptor relationships for PM2.5 during typical pollution episodes in the Pearl River Delta city cluster, China

Located in the Southern China monsoon region, pollution days in Pearl River Delta (PRD) were classified into “Western type”, “Central type” or “Eastern type”, with a relative percentage of 67%, 24% and 9%, respectively. Using this classification system, three typical pollution events were selected for numerical simulations using the WRF-Chem model. The source sensitivity method for anthropogenic emissions of PM2.5 and its precursors was applied to identify the source-receptor relationships for PM2.5 among 9 cities in PRD. For “Western type” case, the PRD region was under control of a high-pressure system with easterly prevailing winds. The PM2.5 concentrations in the western PRD region were higher than those in the eastern region, with emissions from cities in the eastern PRD region having higher contributions. Within the PRD's urban cluster, PM2.5 in Huizhou, Dongguan and Shenzhen was mainly derived from local emissions, whereas the PM2.5 in the other cities was primarily derived from external transport. For “Eastern type” case, the PRD was influenced by Typhoon Soulik with westerly prevailing winds. Emissions from cities in the western PRD region had the highest impacts on the overall PM2.5 concentration. PM2.5 in Jiangmen and Foshan was primarily derived from local emissions. Regarding “Central type” case, the PRD region was under control of a uniform pressure field with low wind speed. PM2.5 concentrations of each city were primarily caused by local emissions. Overall, wind flows played a significant role in the transport and spatial distribution of PM2.5 across the PRD region. Ideally, local governments would be wise to establish joint prevention and control measures to reduce regional atmospheric pollution, especially for “Western type” pollution.

Source-receptor probability of atmospheric long-distance dispersal of viruses to Israel from the eastern Mediterranean area.

Viruses that affect the health of humans and farm animals can spread over long distances via atmospheric mechanisms. The phenomenon of atmospheric long-distance dispersal (LDD) is associated with severe consequences because it may introduce pathogens into new areas. The introduction of new pathogens to Israel was attributed to LDD events numerous times. This provided the motivation for this study which is aimed to identify all the locations in the eastern Mediterranean that may serve as sources for pathogen incursion into Israel via LDD. This aim was achieved by calculating source-receptor relationship probability maps. These maps describe the probability that an infected vector or viral aerosol, once airborne, will have an atmospheric route that can transport it to a distant location. The resultant probability maps demonstrate a seasonal tendency in the probability of specific areas to serve as sources for pathogen LDD into Israel. Specifically, Cyprus' season is the summer; southern Turkey and the Greek islands of Crete, Karpathos and Rhodes are associated with spring and summer; lower Egypt and Jordan may serve as sources all year round, except the summer months. The method used in this study can easily be implemented to any other geographic region. The importance of this study is the ability to provide a climatologically valid and accurate risk assessment tool to support long-term decisions regarding preparatory actions for future outbreaks long before a specific outbreak occurs.