Impact of land cover transformation on urban heat islands in Harbin, China.

At the local and regional climate scale, one of the most studied environmental issues is urban heat island (UHI). UHI is a thermal anomaly caused by temperature differences between urban and rural settings, which adds heat to the atmosphere and makes people feel uncomfortable. This study explores the influence of new land-cover data on UHI simulations using the high-resolution Weather Research and Forecasting (WRF) model coupled with the single-layer urban canopy model (SLUCM) in the city of Harbin. A comparison was performed between the new Tsinghua University (TU) land cover dataset with the default United States Geological Survey (USGS) and Moderate Resolution Imaging Spectroradiometer (MODIS) land cover datasets. The results of this study revealed that the new TU land cover data had better representation and more realistic land cover changes than the default datasets. The diurnal, seasonal, and long-term nighttime UHIs of air and surface temperatures were higher than the daytime UHIs for both downtown Harbin and the satellite towns. We discovered that coal-burning during winter had a significant influence on UHI in Harbin. Moreover, the results from our buffer revealed a rapid increase in the UHIs of satellite towns, thus revealing the need to focus on the effects of UHI in satellite towns in the future. Therefore, the timely updating of land cover datasets in the WRF model and implementing mitigation strategies will help improve the urban climatic comfort.

Theoretical insights into the gas/heterogeneous phase reactions of hydroxyl radicals with chlorophenols: Mechanism, kinetic and toxicity assessment.

Emission of 2-chlorophenols (2-CPs) can cause serious air pollution and health problems. Here, the reaction kinetics and products of key radicals in 2-CPs photo-oxidation are explored in both gaseous and heterogeneous reactions. Quantum chemical calculations show that •OH-addition pathways are more preferable than H-abstraction pathways in gas phase, while that is opposite in heterogeneous phase. At 298 K, the overall rate coefficients of the title reactions in gas and heterogeneous phases are 3.48 × 10-13 and 2.37 × 10-13 cm3 molecule-1 s-1 with half-lives of 55.3 h and 81.2 h, respectively. The strong H-bonds between linear Si3O2(OH)8 and 2-CPs change the energy barriers of initial •OH-addition and H-abstraction reactions, resulting in the competition between heterogeneous reactions and gas phase reactions. The products in heterogeneous reactions are chloroquinone and HONO, which can cause atmospheric acid deposition and eco-toxicity. In gas phase, self-cyclization of alkoxy radical (RO•) leads to formation of •HO2 and highly­oxygenated molecules, which cause formation of secondary organic aerosol. It is emphasized that oxidation of 2-CPs by •OH leads to formation of more toxic products for aquatic organisms. Therefore, more attention should be focused on the products originated from •OH-initiated reactions of (2-)CPs in gaseous and heterogeneous reactions.

Impact of climate change on snowmelt runoff in a Himalayan basin, Nepal.

The Hindu Kush Himalaya (HKH) is one of the major sources of fresh water on Earth and is currently under serious threat of climate change. This study investigates the future water availability in the Langtang basin, Central Himalayas, Nepal under climate change scenarios using state-of-the-art machine learning (ML) techniques. The daily snow area for the region was derived from MODIS images. The outputs of climate models were used to project the temperature and precipitation until 2100. Three ML models, including Gated recurrent unit (GRU), Long short-term memory (LSTM), and Recurrent neural network (RNN), were developed for snowmelt runoff prediction, and their performance was compared based on statistical indicators. The result suggests that the mean temperature of the basin could rise by 4.98 °C by the end of the century. The annual average precipitation in the basin is likely to increase in the future, especially due to high monsoon rainfall, but winter precipitation could decline. The annual river discharge is projected to upsurge significantly due to increased precipitation and snowmelt, and no shift in hydrograph is expected in the future. Among three ML models, the LSTM model performed better than GRU and RNN models. In summary, this study depicts severe future climate change in the region and quantifies its effect on river discharge. Furthermore, the study demonstrates the suitability of the LSTM model in streamflow prediction in the data-scarce HKH region. The outcomes of this study will be useful for water resource managers and planners in developing strategies to harness the positive impacts and offset the negative effects of climate change in the basin.

Occurrence, distribution and human exposure of phthalic esters in road dust samples across China.

203 road dust samples were conducted across China covering 28 provinces from January to February，2016 to comprehensively investigates the occurrence, distribution and human exposure of 21 phthalic esters (PAEs). The concentration of Σ21PAEs in road dust ranged from 2.3 to 531 mg/kg, with a mean concentration of 64.1 ± 57.2 mg/kg. DEHP, DnBP and DiBP were the dominant components accounting for 63.3-97.9% (mean: 92.1%) of the Σ21PAEs. Significant Pearson correlation (r = 0.51, p < 0.0001) between Σ21PAEs concentrations and longitude demonstrated a distinguished geographical trend. Higher concentration of PAEs in sidewalk (SW) and trunk road (TR) may reflect influence of human activities such as shoe wear and traffic load. Significant differences were found among different human activities area (urban commercial, urban residential, and suburbs/rural). For total daily intake of Æ©21PAEs via street dust, children had the highest exposure risk followed by teenagers and adults with the median values of 160.8, 43.6, and 37.7 ng/kg-bw/day, respectively. The maximum exposure risk of PAEs calculated based on measurement and simulation were all far below reference values. The sensitivity analysis results demonstrated that concentrations, ingestion rate (IR) and fraction of PAEs absorbed in the skin (AF) were most important parameters on the assessment of exposure risk of PAEs via street dust. Specific parameters based on China and Chinses population is needed to obtain more reliable exposure risk via street dust.

Long-term characteristics of criteria air pollutants in megacities of Harbin-Changchun megalopolis, Northeast China: Spatiotemporal variations, source analysis, and meteorological effects.

The hourly concentration of six criteria air pollutants in the Harbin-Changchun region were used to investigate the status and spatiotemporal variation of target air pollutants and their relationships with meteorological factors. The annual concentrations of particulate matters during 2013-2017 were two times higher than the Chinese Ambient Air Quality Standards (CAAQS) Grade Ⅱ. The annual O3 concentration increased by two times during 2013-2018 in Harbin. The concentration of PM, SO2, NO2, and CO depicted a similar seasonal trend with an order of winter > autumn > spring > summer. The consistent interannual variation trends of PM2.5/CO, NO2 and SO2 indicated that the formation of secondary inorganic aerosols in the annual scale was dominated by the concentrations of NO2 and SO2. The interannual variations of the individual meteorological factors causing on PM2.5 and O3 during 2013-2018 varied significantly in seasonal scale. The interannual variations were stable in annual scale indicating that the continuous decline of PM2.5 during 2014-2018 can be attributed to the comprehensive and strict prohibition of small coal-fired boilers and straw burning in the study area. Meanwhile, the increase in O3 during 2013-2018 in the study area were mainly attributed to the rapid growth of the emission of its precursor (VOCs and NOx). The influence of meteorology on PM2.5 and ozone were the most stable and strongest in winter than that in the other three seasons.

Polycyclic aromatic hydrocarbons and their nitro-derivatives in urban road dust across China: Spatial variation, source apportionment, and health risk.

As an essential carrier of hazardous substances, fugitive road dust has become a severe issue in China. In this study, 212 road dust samples from 53 cities in China were collected to comprehensively investigate the spatial variations, potential sources, and cancer risk of 16 polycyclic aromatic hydrocarbons (PAHs) and 16 nitro-PAHs. The total PAHs concentrations ranged from 0.07 to 345 µg/g dry weight, which is at a moderate level compared to other regions in the world. The mean concentration of Σ16nitro-PAHs was 111 ± 115 ng/g, which is 2-3 orders of magnitude lower than that of Σ16PAHs. A clear geographical trend of dust PAHs and nitro-PAHs was observed in the northeast, north, and east coastal regions of China at a higher level. Moreover, a significant correlation between latitude and PAHs/nitro-PAHs revealed the influences of outdoor temperature and coal combustion for heating in the different regions on the emission and reaction of PAHs and nitro-PAHs. The secondary formation of most nitro-PAHs increases with a decrease in latitude indicated that solar radiation and temperature are important factors on secondary formation of nitro-PAHs. The average concentration of total PAHs and their derivatives in trunk road samples were statistically higher than those in other road samples (p < 0.05), indicating the influence of traffic load on target compound concentration. Generally, the primary sources of PAHs in the road dust samples were coal combustion (23.9%), vehicles (57.1%), and wood/biomass combustion (19.0%). For nitro-PAHs, the main sources were secondary formation (30.9%), biomass/coal combustion (28.4%), and vehicles (44.9%). Furthermore, a moderate potential carcinogenic risk due to PAHs and nitro-PAHs in the dust samples was found in China.

Occurrence, composition profiles and risk assessment of polycyclic aromatic hydrocarbons in municipal sewage sludge in China.

A nationwide survey, including 75 sludge samples and 18 wastewater samples taken from different wastewater treatment plants (WWTPs) from 23 cities, was carried out to investigate the occurrence and composition profiles of polycyclic aromatic hydrocarbons (PAHs) in China. In total, the concentrations of ∑16PAHs in sludge ranged from 565 to 280,000 ng/g (mean: 9340 ng/g) which was at a moderate level in the world. The composition profiles of PAHs were characterized by 3- and 4-ring PAHs in textile dyeing sludge and 4- and 5-ring PAHs in domestic sludge. Significant variations in regional distribution of PAHs were observed. Both the principal components analysis and diagnostic ratios revealed that vehicle exhaust, coal and natural gas combustion were the main sources of PAHs in China. The estimated concentrations of PAHs were 3820 ng/L and 1120 ng/L in influents and effluents of the WWTPs, respectively. The high toxic equivalent quantity (TEQ) values of PAHs are ascribed to the high PAH levels. Risk quotient values (RQs) in sludge indicated that there was low potential risk to soil ecosystem after sludge had been applied one year except for indeno [1,2,3-cd]pyrene (IcdP) detected in Huaibei, Anhui province.