Characteristics, sources and health risk assessment of airborne particulate PAHs in Chinese cities: A review.

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds composed of at least two benzene rings. This paper reviews the characteristics, sources and health risk of airborne particulate PAHs in Chinese cities. The airborne particulate PAH concentrations varied from 3.35 to 910 ng m-3, with an average of 75.0 ng m-3, and the pollution level of PAHs in northern cities was generally higher than that in southern cities. The PAH concentrations in different cities underwent similar seasonal variations, with high concentrations in the winter and relatively low concentrations in the summer. Many factors, such as meteorological conditions and source emissions, influenced the spatiotemporal pattern of PAHs. High temperatures, frequent flow exchanges, abundant rainfall and strong solar radiation reduced the level of particulate PAHs in the atmosphere. The historical changes in the level of airborne particulate PAHs in four cities were analyzed. The PAH concentrations in Beijing and Taiyuan presented a trend of first increasing and then decreasing, while the level of particulate PAHs in Nanjing and Guangzhou had a decreasing tendency from year 2000-2015. The airborne particulate PAHs in cities were derived from several sources, including coal combustion, vehicle emissions, coking industries, biomass burning and petroleum volatilization. The results of a health risk assessment indicated that the incremental lifetime cancer risk (ILCR) for people in the northern cities was higher than that for people in the other regions, especially during the cold season. Moreover, adults were at greater risk than people in other age groups, and the health risk to females was slightly higher than that to males. The potential risk of airborne particulate PAH exposure was relatively high in some cities, and controlling PAH emissions at the source should be required to prevent pollution.

Urban sprawl decreases the value of ecosystem services and intensifies the supply scarcity of ecosystem services in China.

Land use and land cover changes, particularly land take by urbanization, can degrade ecosystems and their capacity to provide humans with numerous benefits, namely, ecosystem services (ES). Many studies on the relationship between urbanization and the supply and demand of ES have been conducted. However, studies on the process and trend of the conflict between ES supply and demand, as well as the spatial differences, are lacking. Developing countries around the world are experiencing rapid urbanization. The aim of this study was to summarize the relationship between urbanization and the supply and demand of ES in China. China has experienced rapid urbanization since the reform and opening up, and the urban population reached 56.10% in 2015. Urban sprawl was twice that of population expansion, and led to a loss in value of ES. We calculated the loss in value of the five ES (food production, water conservation, climate regulation, habitat support and cultural service) due to the increase in construction area by means of spatial analysis. The total loss was US $110.95 billion in China from 1985 to 2015. This result indicated that the increases in construction land area had a negative impact on ES. At the same time, there was a conflict between the scarcity index of ES and their loss in value. The leading cause of this conflict was that economic development was highly dependent on the area of urban construction land. The results suggested that we should adopt "intensive" and "compact" strategic development models, quantify the value of ES, focus on the conflict between the loss in value and ES supply, and try our best to reduce the decline in ES in the future.

Improving risk management by using the spatial interaction relationship of heavy metals and PAHs in urban soil.

Identifying combined pollution risk areas is difficult because of the complex pollutant sources and heterogeneous soil properties in urban systems. This study used bivariate local Moran's I to analyze the spatial interaction between heavy metals and PAHs, revealed the causes of spatial interaction patterns through PMF, and proposed a risk zoning approach for combined pollution in urban areas. The results showed that both heavy metals and PAHs had high spatial heterogeneity in urban soil. Bivariate LISA maps revealed the spatial interactions between heavy metals and PAHs. The historical area was the hotspot of combined pollution. The overlay of pollutant sources and sinks was responsible for the spatial interaction patterns of combined organic and inorganic pollution. Coal consumption was the main emission source for heavy metal and PAHs pollution, accounting for 31% and 21%, respectively. We used bivariate LISA as the auxiliary variable to reduce the uncertainty of identification combined pollution risk zones. More than 11% of the total area clustered significantly where concentration of both heavy metals and PAHs ware in excess of the risk threshold. This study indicates that we can provide better decision-making support for soil risk management based on the knowledge derived from spatial interaction analysis.

Modeling of Trace Metal Migration and Accumulation Processes in a Soil-Wheat System in Lihe Watershed, China.

Samples of wheat and soil were collected in the Lihe watershed in East China, the migration and accumulation processes of four common trace metals (Cu, Pb, Cd and Ni) in each part of the wheat plant (root, stem, leaf and grain) were analyzed, and a mechanistic model was proposed to simulate these processes based on wheat growth techniques. Model results show that Cu and Cd migrate more easily with wheat grains, while most Pb and Ni accumulate in roots. Modeling results were shown to be relatively good, with an error of 25.29% in value and 26.38% in fluctuation, and had smaller dispersion degree than actual measurement results. Monte Carlo simulation results also match quite well with actual measurement results, and modeling results are slightly smaller in the simulation of Leaf-Cu, Grain-Cu and Leaf-Ni. Trace metal pollution risk in wheat is evaluated based on this model; our results show that the northwest and northeast parts in the research area are not suitable for growing wheat. In general, this model is relatively accurate, and can evaluate the wheat pollution risk before seeding wheat, providing scientific references for the early selection of wheat safety sowing areas.