Refractory black carbon aerosols in rainwater in the summer of 2019 in Beijing: Mass concentration, size distribution and wet scavenging ratio.

Black carbon (BC) aerosols in the atmosphere play a significant role in climate systems due to their strong ability to absorb solar radiation. The lifetime of BC depends on atmospheric transport, aging and consequently on wet scavenging processes (in-cloud and below-cloud scavenging). In this study, sequential rainwater samples in eight rainfall events collected in 2 mm interval were measured by a tandem system including a single particle soot photometer (SP2) and a nebulizer. The results showed that the volume-weighted average (VWA) mass concentrations of refractory black carbon (rBC) in each rainfall event varied, ranging from 10.8 to 78.9 µg/L. The highest rBC concentrations in the rainwater samples typically occurred in the first fraction from individual rainfall events. The geometric mean median mass-equivalent diameter (MMD) decreased under precipitation, indicating that rBC with larger sizes was relatively aged and preferentially removed by wet scavenging. A positive correlation (R2 = 0.73) between the VWA mass concentrations of rBC in rainwater and that in ambient air suggested the important contribution of scavenging process. Additionally, the contributions of in-cloud and below-cloud scavenging were distinguished and accounted for 74% and 26% to wet scavenging, respectively. The scavenging ratio of rBC particles was estimated to be 0.06 on average. This study provides helpful information for better understanding the mechanism of rBC wet scavenging and reducing the uncertainty of numerical simulations of the climate effects of rBC.

Analysis of dose monitoring for external exposure to radiology in hospital workers from 2010 to 2018.

OBJECTIVE: To investigate the individual level of radiation exposure in hospital workers from 2010 to 2018. METHODS: Oral radiology workers in our hospital including medical imaging technicians and radiation therapists from 2010 to 2018 were selected as the subjects of investigation. The oral radiological workers were monitored quarterly according to the level of external exposure via individual dose monitoring standards. The monitoring data were aggregated, analyzed and evaluated. RESULTS: A total of 531 hospital radiology workers were monitored from 2010 to 2018. The rate of effective monitoring per year for medical imaging technicians and radiation therapists was 97.35% and 97.47%, respectively. The average collective effective dose was 8.511 mSv, and annual effective dose per capita was 0.148 mSv. The highest collective effective dose was in 2017, while the highest annual effective dose per capita was in 2010. The annual effective dose per capita for medical imaging technicians was lower than that for radiation therapists. The abnormal rate of personal doses of radiation therapists was higher than that for medical imaging technicians. The collective effective dose changes in the two types of radiation workers were monitored from 2010 to 2018, showing an increased trend. The fluctuations of annual effective dosing per capita monitored from 2010 to 2018 in radiation therapists was more significant than that in medical imaging technicians. CONCLUSIONS: Oral radiation workers monitored were all far below the dose limit of 20 mSv, which indicated that the working environment of oral radiation workers in our hospital was safe with good radiation condition and protection.

Affinity zone identification approach for joint control of PM2.5 pollution over China.

In recent years, the Chinese government has made great efforts to jointly control and prevent air pollution, especially fine particulate matter (PM2.5). However, these efforts are challenged by technical constraints due to the significant temporal and spatial heterogeneity of PM2.5 across China. In this study, the Affinity Zone Identification Approach (AZIA), which combines rotated principal component analysis (RPCA) with revised clustering analysis, was developed and employed to regionalize PM2.5 pollution in China based on data from 1496 air quality monitoring sites recorded from 2013 to 2017. Two clustering methods, cluster analysis with statistical test (CAST) and K-center-point (K-medoids) clustering, were compared and revised to eliminate unspecified sites. Site zonation was finally extended to the municipality scale for the convenience of the controlling measures. The results revealed that 17 affinity zones with 5 different labels from clean to heavily polluted areas could be identified in China. The heavily polluted areas were mainly located in central and eastern China as well as Xinjiang Province, with regional average annual PM2.5 concentrations higher than 66 µg/m3. The new approach provided more comprehensive and detailed affinity zones than obtained in a previous study (Wang et al., 2015b). The North China Plain and Northeastern China were both further divided into northern and southern parts based on different pollution levels. In addition, five affinity zones were first recognized in western China. The findings provide not only a theoretical basis to further display the temporal and spatial variations in PM2.5 but also an effective solution for the cooperative control of air pollution in China.

[Observational Study of Air Pollution Complex in Nanjing in June 2014].

Studying the evolution of secondary inorganic aerosols, which are important components of PM2.5, is crucial to improving our understanding about the air pollution in big cities. This study investigates the evolution and factors of secondary inorganic aerosols based on two pollution incidences in Nanjing in June 2014. A significant characteristic of air pollution complex with the coexistence of higher concentrations of both PM2.5 and ozone is observed. In the earlier stage of the pollution episode, ozone concentrations were high, which could exceed 250, triggering a stronger oxidation in the atmosphere and a higher production potential of nitric acid that leads to the quick production of nitrate. In the later period of the pollution episode, relative humidity played an essential role. An increase in relative humidity would result in a sharp decrease in the theoretical product of the partial pressures of NH3 and HNO3, especially when relative humidity exceeds the mutual deliquesce relative humidity that makes it easier to form nitrate. The difference in the theoretical and observational partial pressure product could characterize the evolution of nitrate perfectly.

Below-cloud wet scavenging of soluble inorganic ions by rain in Beijing during the summer of 2014.

Wet deposition is one of the most important and efficient removal mechanisms in the reduction of air pollution. As a key parameter determining wet deposition, the wet scavenging coefficient (WSC) is widely used in chemical transport models (CTMs) and reported values have large uncertainties. In this study, a high-resolution observational dataset of the soluble inorganic aerosols (SO42-, NO3- and NH4+, hereafter SNA) in the air and in rainwater during multiple precipitation events was collected using sequential sampling and used to estimate the below-cloud WSC in Beijing during the summer of 2014. The average concentrations of SNA in precipitation during the observational period were 7.9 mg/L, 6.2 mg/L and 4.6 mg/L, with the contributions from below-cloud scavenging constituting 56%, 61% and 47% of this, respectively. The scavenging ratios of SNA (i.e., the ratio of the concentrations in rain to concentrations in the air) were used with the height of the cloud base and the precipitation intensity to estimate the WSC. The estimated WSC of SO42- is comparable to that reported elsewhere. The relationship between the below-cloud WSC and the precipitation intensity followed an exponential power distribution (K=aPb) for SNA. In contrast to previous studies, this study considers the differences between the chemical compositions of the SNA, with the highest WSC for NO3-, followed by those of SO42- and NH4+. Therefore, we recommend that CTMs include ion specific WSCs in the future.