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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. [ABSTRACT FROM AUTHOR]

Harbin-Changchun megalopolis (HCM) is a typical representative of the cold urban agglomeration region in China. Although the average annual PM 2.5 concentration has experienced an evolutionary process continuous deterioration to gradual improvement in the past decade, but severe haze episodes still occur during cold winter periods. WRF-CMAQ model and observed dataset of surface PM 2.5 concentration were conducted in this study to identify the drivers of 2015–2021 trends in cold winter surface PM 2.5 in the HCM by separating contributions from anthropogenic emissions and meteorology changes. Meteorological condition change was the dominant driver of 2015–2021 trends in cold winter surface PM 2.5 in the HCM. The years with most unfavorable, typical, and most favorable meteorological conditions for PM 2.5 concentration reduction during January from 2015 to 2021 for the whole HCM region were 2020, 2017, and 2018, respectively. The major controlling meteorological factors that affect the surface PM 2.5 concentration change were relative humidity, maximum wind direction and speed in cold winter in the HCM. In addition, we found that the emission cut policy began to play a practical role in the air quality improvement in the HCM from year of 2018. The emission reduction during the 2017–2021 resulted in an approximately 19% (15.7 μg/m3) decrease of PM 2.5 concentrations in January. Furthermore, sensitivity experiments demonstrated that residential emission cut was the key measures for future air quality improvement in cold winter in the HCM. [Display omitted] • Drivers of 2015–2021 trends in cold winter surface PM 2.5 in the HCM was identified. • RH and wind are dominant meteorological factors affecting PM 2.5 in cold winter. • Residential emission cut was the key measures for future air quality improvement in the HCM. [ABSTRACT FROM AUTHOR]

Atmospheric ammonium and ammonia have brought negative environmental impacts and adverse health effects. However, ammonia emissions are generally less regulated worldwide. This study analyzed ammonium pollution character, quantified the dominant ammonia emission sources, and assessed ammonia reduction potential in urban Harbin (China). The results showed that ammonium recorded low concentration in the non-heating season (1.34 ± 1.57 μg/m3), and recorded sharply increased concentration (6.50 ± 7.02 μg/m3) and relative abundance in the heating season. It was closely correlated with vehicle-related pollutants (CO) in non-heating season, while with biomass burning-related pollutants (K+, Cl−) in the heating season. Bayesian Mixing Model emphasized the increasing contribution of biomass burning and decreasing contribution of fertilizer as the pollution levels escalate. The results from the thermodynamic equilibrium model showed that a 50%–60% ammonium decrease could bring marketable decrements of the aerosol pH, aerosol water content, ammonium nitrate concentration, and inorganic ion mass. The results of this study would provide scientific bases for ammonia emission reduction and haze pollution control in urban Harbin. • Ammonium recorded sharply increased concentration and fraction in heating season. • NH 4 + was scarcely modulated by climate factors, but by anthropogenic emissions. • NH 3 reduction from waste treatment and biomass burning could curb severe pollution. • NH 3 emission has greater reduction potential than SO 2 and NO x for PM 2.5 alleviation. [ABSTRACT FROM AUTHOR]

The meteorological conditions in northeast China exhibit particular characteristics associated with snow cover in winter and dramatic land cover transformations. In this study, the Weather Research and Forecasting Model (WRF) is used to assess the influences of snow albedo and land cover changes on wind speed, temperature, relative humidity, and planetary boundary layer height (PBLH). Two new static geographical datasets, a maximum snow albedo dataset (MSA) developed by Beijing Normal University (BNU_MSA) and a land cover dataset developed by Tsinghua University (TU_LC), are employed for updating previous datasets in WRF. Besides, a case study for local anthropogenic heat (AH) parameters is conducted to examine its influences on temperature in winter. Modeled scenarios for 13 December 2017 to 15 January 2018 show that TU_LC yields a lower mean absolute error of 0.55 m/s for simulated wind speed, suggesting the usefulness of the TU_LC in modeled 10-m wind speed. The change in the wind speed is closely related to land cover transformations occurring over urban and forest regions. The spatially varying temperature agrees well with changes in the MSA. Simulation with updated AH parameters induces higher temperature over downtown Harbin and Changchun. Increasing PBLH is observed as compared with that using default datasets because of increasing temperature and heat fluxes induced by the decreases in MSA. The maximum differences of the wind speed and temperature between updated and default datasets in the verticle direction are confined within 600-m height above the ground surface. • The new land cover and maximum snow albedo datasets show good effects on different modeled meteorological variable as compared with WRF default datasets. • The changes of meteorological variables are significant in urban and forest regions in winter. • The maximum differences of the wind speed and temperature between updated and default datasets in the vertical direction are identified in 600 m height. [ABSTRACT FROM AUTHOR]

Haze pollution in Harbin has been gradually alleviated in recent years, but it is still far from eliminated. Thus, precise and effective emission abatement of main chemical components like nitrate is urgently needed for further haze pollution control. This study aimed to estimate nitrate formation pathways, and the contributions of the emission sources of nitrogen oxide in urban Harbin, based on the measurement of isotope signatures in nitrate and the utilization of an improved Bayesian mixing model. The results showed that nitrate significantly aggravated particulate pollution in the heating season, and its driving role was enhanced as the pollution level increased. This study suggested that homogeneous reaction and heterogeneous reaction were the dominant conversion pathways of nitrate formation in non-heating season and heating season respectively, and the contribution of heterogeneous reaction increased as pollution levels increased. By considering isotope fractionation value (δ15N), this paper emphasized coal combustion as the dominant contributor of nitrogen oxide in urban Harbin, while biomass burning, mobile sources, and biogenic soil emissions played relatively weak roles in nitrate pollution. This study has critical importance to provide scientific theoretical bases for nitrogen oxide reduction in urban Harbin and air quality improvement reference in other severely polluted regions in China. Image 1 • Considering δ15 N fractionation is necessary for accurate NO x source apportionment. • Heterogeneous reaction played a vital role in nitrate formation in heating season. • Coal combustion was the dominant contributor to nitrate pollution in urban Harbin. [ABSTRACT FROM AUTHOR]

Harbin, a cold metropolis of China, frequently endures fine particles (PM 2.5) pollution during its long heating seasons, which has almost become the main environmental issue. To better understand pollution causes, multifaceted factors including the meteorology conditions, secondary transformation, source apportionment and regional transportation, were analyzed based on the definition of three pollution levels and eight pollution episodes. The results showed that chemical species varied dynamically and followed similar trends to PM 2.5 , and secondary organic carbon and nitrate played more significant driving roles in PM 2.5 as the pollution level increased. Five sources were apportioned using the positive matrix factorization model, and the order of importance for the entire study period was as follows: secondary aerosol, traffic emissions, biomass burning, mineral dust, and coal combustion. The PM 2.5 in Harbin is mainly affected by transportation in the Harbin-Changchun megalopolis and slightly affected by long-distance transmission from the northwestern region of Harbin. A pollution episode in the fall was quite significant, as it was characterized by long duration time and extremely high pollutant levels, and was most likely attributed to extensive emissions from biomass burning and enhanced secondary transformation. The pollution episodes in winter were characterized by enhanced heterogeneous reactions and weakened photochemical reactions, which were especially sensitive to synoptic variations, and most likely induced by high relative humidity (>60%), low wind speed (3 m/s), suppressed planetary boundary layer height (<200 m), and strengthened inversion layer under the control of high-pressure systems. Meanwhile, the episodes in spring were characterized by high proportions of mineral dust, chlorine, and potassium, which was mostly attributed to the prevailing dust events, stronger biomass burning activities, and favorable transportation under low-pressure systems. Image 1 • Multifaceted factors were analyzed to explore the cause of PM 2.5 pollution episodes. • Secondary organic carbon and nitrate were two most abundant chemical components. • Biomass burning and secondary aerosol contributes most to fine particle pollution. • Regional transportation and adverse weather promote pollution formation. [ABSTRACT FROM AUTHOR]