Contribution Of Different Sources Research Articles

Optimization of a volatile organic compound control strategy in an oil industry center in Canada by evaluating ozone and secondary organic aerosol formation potential

Volatile organic compounds (VOCs) play a vital role in the formation of photochemical smog and haze in large urban environments. Previous source apportionment studies have focused on the contribution of different sources to VOC concentration with a view to pinpointing the major culprits for effective emission mitigation. However, different VOC sources may have different ozone (O3) and secondary organic aerosol (SOA) formation potentials. From a control perspective, it would be more rational to consider the role of individual VOC sources in secondary pollution; therefore, here, we propose a tiered source identification method that considers the formation potentials of O3 and SOA, which we applied in Calgary, Alberta, a site under the influence of multiple competing VOC sources. The pollution characteristics, secondary pollutant formation potential, and geographical origin of VOC sources were investigated over a five-year period. Seven major sources were identified using the positive matrix factorization (PMF) model, among which vehicle exhausts and solid fuel combustion were the dominant VOC sources responsible for O3 (60%) and SOA (63%) formation. Combustion of both liquid fuel (gasoline and diesel) and solid fuel (wood and coal) has exceeded the contribution of oil and gas production and become the top contributor to O3 and aerosol pollution in Calgary. This finding is consistent with the significant reduction (32.2–99.8%) in oil and gas production in Calgary over the period of 2013–2017. The source apportionment results show that the primary VOC source has shifted from conventional oil and gas extraction to a mixture of vehicle exhausts and oil and gas extraction, indicating the effectiveness of emission control measures taken in the energy sectors. Moreover, regionally transported VOCs from combustion sources in southeastern British Columbia have greatly increased the VOC level and secondary pollutant formation in Calgary. To effectively alleviate secondary pollution problems, the performance of joint pollution control measures has been suggested by the governments of both Alberta and British Columbia. These findings reveal that the tiered source identification strategy combining the traditional receptor model with socioeconomic factors, emission inventory, and source region analysis is a robust and promising tool for the interpretation of source apportionment results and optimization of secondary pollution control.

Heavy metals in indoor dust: Spatial distribution, influencing factors, and potential health risks

Given the large proportion of time that people spend indoors, the potential health risks posed by heavy metals in the indoor environment deserve greater attention. A global-scale assessment of heavy metal contamination in indoor dust was conducted in this study based on >127 articles published between 1985 and 2019. The pollution levels, spatio-temporal variations, sources, bioaccessibilities, influencing factors, and health risks of heavy metals associated with indoor dust were analyzed. Children's blood lead levels (BLLs) were also estimated using the integrated exposure uptake biokinetic model. The results indicated that the median concentrations of Cu and Zn in 71.9% and 71.0% of the study sites surpassed the corresponding permissible limits, 100 and 300 mg/kg, respectively; thus, their control should be given priority. Heavy metal concentrations in indoor dust from different areas of the world varied greatly, which was closely associated with the type of local human activities, such as mining, melting, e-waste recycling and Pb-related industries. The bioaccessibilities of some key elements, e.g., Pb, Cd, Cu, and Zn, in household dust were high. The levels of heavy metals in indoor dust were mainly affected by a combination of outdoor and indoor sources and related critical factors, and future studies should focus on quantifying the contributions of different sources. Based on the health risk assessment, dust Pb exposure is a major health concern in e-waste recycling areas, which warrants greater attention. 49.8%, 36.8% and 14.4% of study sites showed BLLs exceeding 35 μg/L (threshold limit in Germany), 50 μg/L (threshold limit in the USA), or 100 μg/L (threshold limit in China), respectively. Finally, Pb exposure from indoor dust represents a major contributor to children's blood Pb poisoning in many developing countries. This study details the overall heavy metal contamination status of indoor dust and provides insights for policymakers with respect to pollution prevention measures.

Production of superoxide and hydrogen peroxide in the mitochondrial matrix is dominated by site IQ of complex I in diverse cell lines

Understanding how mitochondria contribute to cellular oxidative stress and drive signaling and disease is critical, but quantitative assessment is difficult. Our previous studies of cultured C2C12 cells used inhibitors of specific sites of superoxide and hydrogen peroxide production to show that mitochondria generate about half of the hydrogen peroxide released by the cells, and site IQ of respiratory complex I produces up to two thirds of the superoxide and hydrogen peroxide generated in the mitochondrial matrix. Here, we used the same approach to measure the engagement of these sites in seven diverse cell lines to determine whether this pattern is specific to C2C12 cells, or more general. These diverse cell lines covered primary, immortalized, and cancerous cells, from seven tissues (liver, cervix, lung, skin, neuron, heart, bone) of three species (human, rat, mouse). The rate of appearance of hydrogen peroxide in the extracellular medium spanned a 30-fold range from HeLa cancer cells (3 pmol/min/mg protein) to AML12 liver cells (84 pmol/min/mg protein). The mean contribution of identified mitochondrial sites to this extracellular hydrogen peroxide signal was 30 ± 7% SD; the mean contribution of NADPH oxidases was 60 ± 14%. The relative contributions of different sites in the mitochondrial electron transport chain were broadly similar in all seven cell types (and similar to published results for C2C12 cells). 70 ± 4% of identified superoxide/hydrogen peroxide generation in the mitochondrial matrix was from site IQ; 30 ± 4% was from site IIIQo. We conclude that although absolute rates vary considerably, the relative contributions of different sources of hydrogen peroxide production are similar in nine diverse cell types under unstressed conditions in vitro. Identified mitochondrial sites account for one third of total cellular hydrogen peroxide production (half each from sites IQ and IIIQo); in the mitochondrial matrix the majority (two thirds) of superoxide/hydrogen peroxide is from site IQ.

Airborne Lead (Pb) From Abandoned Mine Waste in Northeastern Oklahoma, USA.

Active and abandoned mines pose serious health threats to humans, aquatic, and terrestrial biota. Northeastern Oklahoma, home to a number of Native American Tribes, is part of the well‐known Tri‐State Mining District. More than 100 years of mining production in this area has left numerous, large chat piles in the surrounding environment. Despite numerous studies and efforts on the restoration of metal contamination in this area, no studies have attempted to distinguish the contributions of different sources, particularly from the atmospheric deposition, of metals to the aquatic environment. Here, we analyzed the atmospheric deposition of Pb from Picher, a town surrounded by chat piles, and Tulsa, a primary metropolitan area in northeastern Oklahoma, from 2010 to 2016. We found that chat piles in Picher contain ~20% and 6% of fine particles that are subjective to windborne transport and human inhalation, respectively, and these fine particles contain disproportionally high concentrations of Pb. Despite the absence of industrial and human activities, airborne Pb in Picher is 2–5 times higher than that of Tulsa. A conservative estimate showed that airborne Pb may contribute up to 10% of annual Pb mass flux to a lake 18 km away from the chat piles in Picher and probably a much higher contribution for soil and water located adjacent to Picher. Despite known limitations, our study represents the first attempt to evaluate the significance of Pb‐laden airborne particulate matter from a large‐scale abandoned mining area where the humans are particularly vulnerable to metal exposure.

Quantifying source contributions for indoor CO2 and gas pollutants based on the highly resolved sensor data

Household air pollution is the dominant contributor to population air pollutant exposure, but it is often of less concern compared with ambient air pollution. One of the major knowledge gaps in this field are detailed quantitative source contributions of indoor pollutants, especially for gaseous compounds. In this study, temporally, spatially, and vertically resolved monitoring for typical indoor gases including CO2, CO, formaldehyde, methane, and the total volatile organic compounds (VOCs) was conducted to address pollution dynamics and major sources in an urban apartment. The indoor concentrations were significantly higher than the simultaneously measured outdoor concentrations. A new statistic approach was proposed to quantitatively estimate contributions of different sources. It was estimated that outdoor CO2 contributed largely to the indoor CO2, while main indoor sources were human metabolism and cooking. Outdoor infiltration and cooking contributed almost equally to the indoor CO. The contribution of outdoor infiltration to methane was much higher than that to formaldehyde. Cooking contributed to 24%, 19%, and 25% of indoor formaldehyde, methane, and VOCs, whereas the other unresolved indoor sources contributed 61%, 19%, and 35% of these pollutants, respectively. Vertical measurements showed that the uplifting of hot air masses led to relatively high concentrations of the pollutants in the upper layer of the kitchen and in the other rooms to a lesser extent.

Identifying the seasonal variability in source of groundwater salinization using deuterium excess- a case study from Mewat, Haryana, India

Study regionMewat (renamed as Nuh) district of Haryana, India having geographical area of 1507 km2, comes under semi arid climatic conditions and Aravali hill ranges separates it from Rajasthan state. Study focusGroundwater salinization is an emerging threat to water management. Understanding the sources of salinization, and their relative contributions by different sources and seasonal variability has become priority for planning best practices in water management and suggesting remedial measures. For identifying the sources of salinization, the direct application of the relationship between δ18O and δD is limited as it depends upon initial isotopic composition showing no isotopic variation in the mineral dissolution process. The present study advocates the use of deuterium excess which is independent of initial isotopic composition and extends this concept for identifying the relative contribution of different sources towards seasonal variability in salinization. New hydrological insights for the regionThe district showed an average salinity of 6.7 g/L in pre-monsoon; 7.3 g/L in monsoon and 7.4 g/L in post-monsoon season thus a variability of 0.7 g/L observed. The area affected by the salinization (>2 g/L) also registers an increase from 86 % (pre-monsoon) to 99 % (post-monsoon) period. Mineral dissolution is found to be responsible for overall groundwater salinization with contribution of 97 %, declined to 86 % in post monsoon. In post monsoon season, contributions from initial salinity and evapoconcentration towards salinization increased by 8% and 3%, respectively.

Risk factors for sporadic toxoplasmosis: A systematic review and meta-analysis

Toxoplasmosis is considered as the most prevalent parasitic zoonotic infection worldwide. The parasitic cycle is mostly known, but the relative contribution of different sources and pathways of transmission was not previously studied by a meta-analysis. A systematic review and a meta-analysis of case-control, cohort, and cross-sectional studies were performed to determine the main risk factors associated with sporadic Toxoplasma infection. Suitable scientific articles were identified through a systematic literature search and subjected to a methodological quality assessment. Mixed-effects meta-analysis models were adjusted by population type – children, mixed population, and pregnant women – to appropriate data partitions. 187 primary studies passed the quality assessment stage, investigating risk factors for sporadic infection with Toxoplasma gondii conducted between 1983 and 2016. Cases were defined by serology.The meta-analysis of Toxoplasma sporadic infections revealed the significance of transmission by environmental factors such as contact with soil and contact with animals, in particular cats. The consumption of raw or undercooked meat and unwashed vegetables significantly increased the odds of acquiring the disease. Shellfish and raw milk were identified as significant sources of toxoplasmosis. Almost all meat categories were identified as risk factors: pork, poultry, beef, processed meat, lamb, and game meat. Contaminated drinking water may play a role in the acquisition of infection. Moreover, the lack of hygiene in preparing food was identified as a risk factor. A significant risk factor for pregnant women is traveling abroad. Lastly, blood transfusion (in pregnant women) and immunocompromised conditions were found associated with positive serology. The broad definition of exposures and the use of serology for the case definition are the main limitations for the interpretation of the results of this meta-analysis. The transmission pathways require further investigations using longitudinal studies and subtyping approaches.

The effects of a known exposure source on Pb isotopes in bones from Pb-dosed cows

Pb accumulates in bone over long periods of time, and the isotopic effects of this accumulation are poorly studied. The use of Pb isotopes in bones as a metric of exposure requires additional constraints on the relationship between the isotopic composition of the exposure source and resulting isotopic composition of the bone. Here, we present a Pb isotope study of two cows that were associated with the blood Pb proficiency testing program at the University of Wisconsin-Madison State Laboratory of Hygiene (WSLH). These two cows were born and raised under the same conditions on the same farm, but were subjected to different levels of Pb exposure during that time period. Pb isotopes were measured in femur bones subsampled from each cow and the Pb isotopic composition of the exposure source (Pb nitrate) used for dosing the animals was also measured. Pb isotopic compositions of nearby (<0.5 km) wild grasses, silage, well water, and other potential environmental sources were measured to obtain the background Pb signal. Our data show that the Pb isotopic compositions of the cow bones reflect a mixture between background Pb sources mostly in the diet and the Pb isotopic composition of the Pb nitrate exposure source. The bones approach but do not attain the Pb isotopic composition of the exposure source at the levels of exposure in this study. Using estimates for daily food and water consumption, we are able to evaluate the relative contributions of different sources of Pb to the isotopic composition of the bone. The data show that the Pb isotopic composition of bone provides a weighted average of bioaccumulated Pb sources. Additional bone major and trace element composition data show that Pb competition with certain other trace elements in Ca substitution sites depends on the degree of Pb exposure. This result has implications for the use of bone in exposure studies, as well as the use of bone to understand background Pb signals in the environment.

Application of Natural Carbon Isotopes for Emission Source Apportionment of Carbonaceous Particulate Matter in Urban Atmosphere: A Case Study from Krakow, Southern Poland

Successful mitigation of air pollution in large cities requires information about the structure of emission sources and their contribution to total atmospheric load. The presented research demonstrates a possibility of application of isotope tracers for the estimation of contribution of different sources to the carbonaceous fraction of PM2.5 (Particulate Matter containing fraction below 2.5 μm) collected in the urban atmosphere of Krakow, Poland during the summer and winter seasons. Isotope mass balance approach was used to perform source apportionment analysis for those two seasons. The analysis showed that the dominant source of the carbonaceous fraction of PM2.5 in Krakow is coal burning during the winter season and biogenic emissions during the summer season. Sensitivity analysis revealed that the uncertainty of the percentage contribution of different sources to the overall carbon load of the analyzed PM2.5 fraction is in order of a few percent.

Spatial Variability and Source Apportionment of Aliphatic Hydrocarbons in Sediments from the Typical Coal Mining Area.

Fifty-four surface sediments from the typical coal mining area were analyzed for pristane, phytane and C8-C40 n-alkanes using gas chromatography-mass spectrometry (GC-MS). The spatial distribution, homolog profiles and source apportionment of aliphatic hydrocarbons were investigated. Bimodal distribution pattern, centered at C16-C20 and C27-C33 n-alkanes, were observed in all sediment samples with an obvious dominance of low molecular weight homologues. Principal component analysis-multiple linear regression (PCA-MLR) was used to predict the contributions of different sources. The result implied that natural input was the main source, contribution of which accounted for 60.8%, and the contributions of different sources were estimated as follow: 21.8% for terrestrial higher plants, 24.1% for algae and photosynthetic bacteria, 14.9% for submerged/floating macrophytes, 23.5% for fossil fuel combustion and 15.7% for petroleum hydrocarbons. Moreover, relatively high median concentrations of fossil fuel combustion were observed in Shou County and Fengtai County, indicating the high contribution of fossil fuel combustion in these two areas.

Coal and biomass burning as major emissions of NOX in Northeast China: Implication from dual isotopes analysis of fine nitrate aerosols

Abstract In recent years, there are still huge amounts of NOx emissions in the Northeast, and this inevitably increases the concentration of aerosol nitrate (NO3−), which plays an important role in atmospheric pollution. Because of the mixed complicated sources of atmospheric NO3−, it is difficult to quantify their contribution, and the use of certain means to identify their sources and pathways is critical to developing effective control measures. Since different sources of NOX have different ranges of δ15N values, δ15N is considered to be a useful tool for identifying the source of aerosol NO3−. But isotope fractionation is produced during the conversion of NOX to NO3−, and δ18O can be used to estimate its isotope fractionation value. In this study, daily PM2.5 samples were collected in four seasons from Northeast China, and their water-soluble ionic components (WSIs), δ15N–NO3- and δ18O–NO3- were analyzed. The isotope fractionation value of δ15N in which NOX was converted to NO3− was estimated and the contribution of different sources was quantified in combination with the Bayesian model. The results showed that NO3− was the most important inorganic ion component in the WSIs with the highest annual average ratio of 21.1%. Both δ15N and δ18O showed higher in winter (δ15N: 13.79‰±2.17‰; δ18O: 70.50‰±10.02‰) than in summer (δ15N: 2.69‰±2.95‰; δ18O: 58.67‰±4.52‰). The daytime OH pathway was considered to play a leading role in nitrate formation, with the annual average contribution of 61.0 ± 18.8%. NOx was mainly from the contribution of coal combustion (34.5%) and biomass burning (34.3%) followed by traffic (19.5%) and biological soil (11.7%). During heating periods, NOx was dominated by coal combustion with the average contribution of 46.9% whereas biomass burning was the most important contributor during non-heating periods (39.5%). Therefore, controlling coal consumption and biomass burning can drastically reduce concentration of aerosol NO3− in Northeast China.

Analysis of Transport Pathways and Potential Sources of Atmospheric Particulate Matter in Zigong, in South of Sichuan Province

Atmospheric particulate matter pollution in Zigong City in southern Sichuan is quite severe. The average concentrations of PM10 and PM2.5 from 2015 to 2018 were (95.42±9.53) μg·m-3 and (65.95±6.98) μg·m-3, with an obvious trend of decline. The concentrations of PM10 and PM2.5 in winter were much higher than in other seasons, with the highest average concentrations being(138.08±52.29) μg·m-3 and (108.50±18.05) μg·m-3 in January, respectively, whereas in summer, the average concentrations were lowest. The average ratio of PM2.5 to PM10 is 69.12%, and the ratio in winter is about 1.17 times that in summer; thus, PM2.5 is mainly responsible for the air pollution. To explore the potential sources of fine particulate matter (PM2.5) in Zigong City and the pollution contributions of different sources in different seasons, the concentration of PM2.5 in Zigong and the daily trajectory after 72 h were calculated and clustered by the combined use of a variety of potential source analysis methods and data. These methods and data included the hybrid single particle lagrangian integrated trajectory (HYSPLIT) model, global data assimilation system (GDAS) meteorological data, potential source contribution analysis (PSCF), and concentration of weight trajectory analysis (CWT). The results showed that the area near Zigong is mostly controlled by southeasterly, westerly, and northwesterly winds in all seasons, and the high PM2.5 concentration is mostly located in the low-wind-speed zone of 0-2 m·s-1. The influence of different seasons and transport routes on PM2.5 pollution in Zigong is significant. In spring, it is mainly affected by short-distance air flow from the west and north; in summer, the pollution mainly comes from the southeast air flow of short-distance transportation; in autumn, it is mainly affected by short-distance transportation air flow from Ziyang, Suining, Chongqing, and Neijiang; and in winter, it is not only affected by the surrounding cities such as Ziyang, Suining, and Neijiang but also by the long-distance transportation air flow from central Tibet. In general, the potential source area of particulate matter in Zigong City is mainly located in the border area between the west of Chongqing and the south of Sichuan. In winter, the main contribution area is at its widest, while in summer, the potential source area is smallest.

Summer–winter contrast in carbon isotope and elemental composition of total suspended particulate matter in the urban atmosphere of Krakow, Southern Poland

Abstract The city of Krakow located in southern Poland ranks among the most polluted urban agglomerations in Europe. There are persisting controversies with respect to impact of different pollution sources operating in Krakow agglomeration on air quality within the city. The presented pilot study was aimed at exploring the possibilities offered by elemental and carbon isotope composition of total suspended particulate matter (TSPM) for better characterization of its sources in Krakow atmosphere. The analyses of carbon isotope composition of total carbon in the investigated TSPM samples were supplemented by parallel analyses of radiocarbon content in atmospheric carbon dioxide (CO2). This study revealed large seasonal variability of carbon isotope composition in the analysed TSPM samples. This large variability reflects seasonally varying contribution of different sources of fossil and modern carbon to the TSPM pool. The elemental composition of TSPM also reveals distinct seasonal variability of the analysed elements, reflecting varying mixture of natural and anthropogenic sources of those elements. A linear relationship between the fossil carbon load in the TSPM samples and the fossil carbon load in the atmospheric CO2 was found, pointing to the presence of additional source of anthropogenic carbonaceous particles not associated with burning of fossil fuels. Wearing of tyres and asphalt pavement is most probably the main source of such particles.

Assessing the Impact of Different Ocean Analysis Schemes on Oceanic and Underwater Acoustic Predictions

AbstractAssimilating oceanic observations into prediction systems is an advantageous approach for real‐time ocean environment characterization. However, its benefits to underwater acoustic predictions are not trivial due to the nonlinearity and sensitivity of underwater acoustic propagation to small‐scale oceanic features. In order to assess the potential of oceanic data assimilation, integrated ocean‐acoustic Observing System Simulation Experiments are conducted. Synthetic altimetry and in situ data were assimilated through a variational oceanographic data assimilation system. The predicted sound speed fields are then ingested in a range‐dependent acoustic model for transmission loss (TL) predictions. The predicted TLs are analyzed for the purpose of (i) evaluating the contributions of different sources to the uncertainties of oceanic and acoustic forecasts and (ii) comparing the impact of different oceanic analysis schemes on the TL prediction accuracy. Using ensemble member clustering techniques, the contributions of boundary conditions, ocean parameterizations, and geoacoustic characterization to acoustic prediction uncertainties are addressed. Subsequently, the impact of three‐dimensional variational (3DVAR), 4DVAR, and hybrid ensemble‐3DVAR data assimilation on acoustic TL prediction at two signal frequencies (75 and 2,500 Hz) and different ranges (30 and 60 km) are compared. 3DVAR significantly improves the predicted TL accuracy compared to the control run. Promisingly, 4DVAR and hybrid data assimilation further improve the TL forecasts, the hybrid scheme achieving the highest skill scores for all cases, while being the most computationally intensive scheme. The optimal scheme choice thus depends on requirements on the accuracy and computational constraints. These findings foster developments of coupled data assimilation for operational underwater acoustic propagation.

Spatiotemporal variations, sources and health risk assessment of perfluoroalkyl substances in a temperate bay adjacent to metropolis, North China

Fourteen perfluoroalkyl substances (PFASs) in fishery organism, surface seawater, river water, rainwater, and wastewater samples collected from Jiaozhou Bay (JZB) in China and its surrounding area were determined to understand their contamination status, sources, health risk, and causes of spatiotemporal variations in the aquatic environment of a temperate bay adjacent to a metropolis. The total concentration of PFASs in 14 species of fishery organisms ranged from 1.77 ng/g to 31.09 ng/g wet weight, and perfluorooctane sulfonate (PFOS) was the dominant PFAS. ∑PFASs concentration in surface seawater ranged from 5.54 ng/L to 48.27 ng/L over four seasons, and dry season (winter and spring) had higher levels than wet season (summer and autumn). Perfluorooctanoic acid (PFOA) was the predominant individual PFAS in seawater, indicating that notorious C8 homologs remained the major PFASs in this region. The seasonal variation in seawater concentrations of three major PFASs, namely, PFOA, perfluoroheptanoic acid, and perfluorononanoic acid, was similar to that of ∑PFASs. However, the seasonal variation of PFOS concentration was different from that of ∑PFASs, with the lowest in winter and the highest in spring. In general, seasonal variations of terrigenous input and water exchange capacity were the main reasons for the spatiotemporal variation of PFASs in the aquatic environment of JZB. Moreover, bioselective enrichment for individual PFAS affected the partition of PFASs in different environment medium. Wet precipitation, sewage discharge, and surface runoff were the main sources of PFASs in this area. Nevertheless, the contribution of different sources to individual PFAS indicated a clear difference, and wastewater and river water were not consistently the most important source for every PFAS. Preliminary risk assessment revealed that the consumption of seafood, especially fish, from JZB might pose a certain extent of health risk to local consumers based on their estimated daily intake of PFASs.

Moisture Source Tagging Confirming the Polar Amplification Effect in Amplifying the Temperature-δ18O Temporal Slope Since the LGM

Stable water isotopologues in paleoclimate archives ( δ 18 O ) have been widely used as an indicator to derive past climate variations. The modern observed spatial δ 18 O -temperature relation in the middle and high latitudes has been used to infer the paleotemperatures changes from ice core data. However, various studies have shown that the spatial slope is larger than the temporal slope at the drill site by a factor of 2. Physically, the different spatial and temporal slope has been suggested to result from the amplified local surface air temperature cooling in the polar region at Last Glacial Maximum (LGM), according to the slope ratio equation derived in our previous study. To explicitly confirm the “polar amplification” effect in understanding the differences between temporal and spatial isotope–temperature relations, here we use the same isotope-enabled atmospheric general circulation model with a moisture-tracing module embedded to quantitatively estimate the contributions of different sources to the precipitated heavy oxygen isotopes in the middle and high latitudes. Our results show that the major sources of δ 18 O in precipitation over middle and high latitudes are from oceans where the sea surface temperature cooling at Last Glacial Maximum (LGM) is less than −2 ° C , while the local moisture sources with a higher cooling can be also relevant for polar regions, such as north Greenland. Additionally, the neglect of the strengthened local inversion layer strength at LGM could be the main cause for the overestimated source temperature cooling by the slope ratio equation, especially for the polar regions in the Northern Hemisphere.

Identifying Nitrate Sources in a Typical Karst Underground River Basin

Underground rivers are an important source of groundwater in karst area. Recently, nitrate pollution of underground rivers has become a serious issue. To identify the sources of nitrate in Guancun typical karst underground river basin, stable isotope techniques (δ15N-NO3-, δ18O-NO3-, and δ18O-H2O) were applied in this study. The contribution rates of different nitrate sources in groundwater were quantitatively identified based on the stable isotope analysis in R (SIAR) model, and the influence of land use type on nitrate distribution and source in watershed water was clarified. The results showed that ① nitrate mainly came from fertilizers, soil organic nitrogen, and manure/sewage based to the isotopic composition of nitrate nitrogen and oxygen isotopes. It was revealed that non-point sources significantly contributed to nitrate in waters of the Guancun underground river basin. ② Nitrification dominated the formation process of nitrate in groundwater, and the initial values of nitrogen and oxygen isotopes were not affected by fractionation. ③ Based on SIAR, the contribution of different sources to nitrate in water in the basin varied seasonally, and the contributions of fertilizer, soil organic nitrogen, and manure/sewage to nitrate were 57.07%, 34.06%, and 8.87% in the wet season and 34.14%, 33.02%, and 32.84% in the dry season, respectively. Overall, the present study quantitatively evaluated the temporal variations of nitrate sources in a typical karst groundwater river basin and provided a theoretical foundation for prevention and control management of non-point source pollution and watershed management in karst areas.

The Effect of the Sectoral Composition of Economic Growth on Rural and Urban Poverty*

We examine the relationship between the sectoral composition of economic growth and the rural‐urban composition of poverty. To this end, we use a cross‐country panel dataset consisting of 146 rural and urban poverty “spells” for 70 low‐ and middle‐income countries. We find that rural (urban) poverty is highly responsive to agricultural (non‐agricultural) productivity growth. The effect of agricultural productivity growth on rural poverty is particularly strong for countries with little dependence on natural resources. We also find that growth in the share of employment in the non‐agricultural sector (i.e. structural transformation) reduces rural poverty, most notably for countries at a low initial level of development. These findings are robust to changes in key assumptions, including using alternative poverty lines. Finally, we use our estimates to examine the past contribution of different sources of economic growth to rural and urban poverty reduction across regions.

Farmers’ perceptions and management of risk in rice/shrimp farming systems in South-West Coastal Bangladesh

Farmers in Bangladesh face considerable risk due to fluctuations in biophysical and economic conditions, but the response to these risks is poorly understood. In particular, there is a need to better understand the endogenous management of risk in the rice/shrimp farming systems that have emerged in the inner coastal zone of Bangladesh. This paper draws on a case study of a typical rice/shrimp farming village in Khulna District to explore: (a) farmers’ perceptions of risks and their management responses, (b) risk-return trade-offs within small-, medium-, and large-farm households, and (c) the role of other farm and non-farm activities in mitigating risks to household livelihoods. Farm-level data were collected through a reconnaissance survey, a village census, household case studies, and a sample survey of 73 households. Representative farm budgets were constructed for the three farm-size classes. The key performance indicators calculated were gross margin (GM), net income (NI), and GM per workday of family labour. The riskiness of the rice/shrimp system was assessed for each farm type using farmers’ estimates of low, normal, and high yields and prices to specify triangular distributions. Cumulative distribution functions (CDFs) for GM, NI, and GM per workday were generated. A whole-farm economic analysis was also conducted to assess the relative contributions of different sources of income for each farm type. With access to saline water for shrimp farming in the dry season and fresh water for rice in the wet season, farmers have developed and progressively adapted an alternating rice/shrimp farming system that has minimised the trade-offs between the two crops and provides a good return to household and village resources for all farm types. The system is subject to significant production and market risks, especially the shrimp component. However, farmers have clearly perceived these risks and ameliorated them through a range of production, marketing, and management strategies. With these risk management practices, the rice/shrimp cropping system is economically viable, given the current variation in yields and prices. The greater risk associated with the shrimp component was offset by the renewed stability of the rice component over the past decade, and the risks of the whole cropping system were offset by other farm and non-farm sources of livelihood. Development interventions need to work with farmers to provide further options (suitable rice varieties, solutions to shrimp disease, improved village and transport infrastructure) if this resilience is to be maintained.

O3 Sensitivity and Contributions of Different NMHC Sources in O3 Formation at Urban and Suburban Sites in Shanghai

Ground-level ozone (O3) pollution is still one of the priorities and challenges for air pollution control in the Yangtze River Delta (YRD) region of China. Understanding the relationship of O3 with its precursors and contributions of different sources in O3 formation is essential for the development of an O3 control strategy. This study analyzed O3 sensitivity to its precursors using a box model based on online observations of O3, non-methane hydrocarbons (NMHCs), nitrogen oxides (NOx), and carbon monoxide (CO) at an urban site and a suburban site in Shanghai in July 2017. Anthropogenic sources of NMHCs were identified using the positive matrix factorization (PMF) receptor model, and then contributions of different sources in O3 formation were estimated by the observation-based model (OBM). The relative incremental reactivity (RIR) values calculated by the OBM suggest that O3 formation at the urban site was in the NMHC-limited regime, while O3 formation at the suburban site tended between the transition regime and the NMHC-limited regime. Vehicular emission and liquefied petrochemical gas (LPG) use or aged air mass were found to be the two largest contributors at the urban and suburban sites in July, followed by paint and solvent use, and the petrochemical industry. However, from the perspective of O3 formation, vehicular emission and paint and solvent use were the largest two contributors at two sites due to the higher RIR values for paint and solvent use. In addition, the influence of transport on O3 sensitivity was identified by comparing O3 sensitivity at the suburban site across two days with different air mass paths. The result revealed that O3 formation in Shanghai is not only related to local emissions but also influenced by emissions from neighboring provinces. These findings on O3–NMHC–NOX sensitivity, contributions of different sources in O3 formation, and influence of transport could be useful for O3 pollution control in the YRD region. Nevertheless, more quantitative analyses on transport and further evaluation of the uncertainty of the OBM are still needed in future.