Regional Air Pollution Episode Research Articles

Impacts of meteorological parameters on the occurrence of air pollution episodes in the Sichuan basin

Episodes of fine-particulate matter (PM2.5) pollution are a widespread and common occurrence in China, and have potentially serious implications for human health. Meteorological conditions play an important role in air quality and influence the formation of regional air pollution episodes. This study applied a new classification method and daily PM2.5 concentration data to (a) evaluate different levels of air pollution in the Sichuan–Chongqing region between 2015 and 2017, and (b) investigate their relationships with meteorological parameters including atmospheric boundary layer height, wind speed, temperature inversion, weather type, and atmospheric transport. We identified a total of 40 air pollution episodes, the most severe of which occurred in winter when the atmospheric layer height was low. These heavy pollution events also coincided with low surface (10 m) wind speeds and temperature inversions, weather conditions that generally result from low pressure over the northwestern Sichuan Basin (90–102° E, 28–36° N) and southerly atmospheric transport.

Spatial distribution of wintertime air pollution in major cities over eastern China: Relationship with the evolution of trough, ridge and synoptic system over East Asia

Hourly air quality index (AQI) data from the Ministry of Environment Protection of China are used to investigate spatial distribution of air pollution in major cities over eastern China (ECN) in winter 2015. The wintertime averaging identifies a pollution center in east Shanxi (IV, the identifier number in Fig. 1), south Hebei (III), west Shandong (V) and Henan (VI) provinces with mean AQI > 100. Four typical types of air pollution spatial distribution are identified. The low level southerly winds are found to be associated with the occurrence of regional air pollution episodes over ECN. The spatial distribution of air pollution is mainly related to the low level meridional wind, which is determined by the specific evolution process of the trough, ridge and synoptic system. The longitudinal position, the deepening (or weakening) and the southward extension (or northward retreat) of the trough over East Asia are the crucial factors determining where the regional air pollution could occur. The influence of precipitation on air pollution is complicated; the initial stage of precipitation with limited precipitation amount promotes the secondary formation and hygroscopic growth of aerosol due to increased supply of moisture, thus favors an aggravation of air pollution; in contrast, only the persisting and intensifying of precipitation are accompanied with more effective wet scavenging and an improvement of air quality. Fireworks emission is found to exacerbate air pollution during the Spring Festival, resulting in a unique distribution of air pollution over a large area of China, suggesting that prohibiting fireworks is necessary under adverse synoptic situation.

Comparisons of two serious air pollution episodes in winter and summer in Beijing

Characteristics of two serious air pollution episodes (9–15 January, as the winter case; and 30 June to 1 July, as the summer case), which occurred in Beijing in 2013 were investigated and compared using multi-method observations and numerical simulations. During these two air pollution episodes, PM2.5 concentrations varied significantly within Beijing, with PM2.5 concentrations in southern parts of Beijing being significantly higher than in northern areas. Typically, heavy air pollution episodes begin in the southern parts and disperse towards the northern parts of Beijing. Clearly, synoptic patterns and the stability of atmospheric circulation patterns were the main factors controlling air pollution in Beijing. During the winter case, a warm center above 900hPa occurred over Beijing. Meanwhile, in the summer case, although there was only a weak inversion, the convective inhibition energy was strong (over 200J/kG). This clearly influenced the duration of the air pollution event. Except for the local accumulation and secondary atmospheric reactions in both cases, regional straw burnings contributed a lot to the PM2.5 concentrations in summer case. Using the CAMx model, we established that regional transport contributed almost 59% to the PM2.5 averaged concentration in Beijing in the winter case, but only 31% in the summer case. Thus, the winter case was a typical regional air pollution episode, while the summer case resulted from local accumulation straw burnings transportation and strong secondary atmospheric reactions. Given that air pollution is a regional problem in China, consistent and simultaneous implementation of regional prevention and control strategies is necessary to improve regional air quality.

Size distribution and mixing state of black carbon particles during a heavy air pollution episode in Shanghai

Abstract. A Single Particle Aerosol Mass Spectrometer (SPAMS), a Single Particle Soot Photometer (SP2) and various meteorological instruments were employed to investigate the chemical and physical properties of black carbon (BC) aerosols during a regional air pollution episode in urban Shanghai over a 5-day period in December 2013. The refractory black carbon (rBC) mass concentrations measured by SP2 averaged 3.2 µg m−3, with the peak value of 12.1 µg m−3 at 04:26 LT on 7 December. The number of BC-containing particles captured by SPAMS in the size range 200–1200 nm agreed very well with that detected by SP2 (R2 = 0.87). A cluster analysis of the single particle mass spectra allowed for the separation of BC-containing particles into five major classes: (1) Pure BC; (2) BC attributed to biomass burning (BBBC); (3) K-rich BC-containing (KBC); (4) BC internally mixed with OC and ammonium sulfate (BCOC-SOx); (5) BC internally mixed with OC and ammonium nitrate (BCOC-NOx). The size distribution of internally mixed BC particles was bimodal. Detected by SP2, the condensation mode peaked around ∼ 230 nm and droplet mode peaked around ∼ 380 nm, with a clear valley in the size distribution around ∼ 320 nm. The condensation mode mainly consisted of traffic emissions, with particles featuring a small rBC core (∼ 60–80 nm) and a relatively thin absolute coating thickness (ACT, ∼ 50–130 nm). The droplet mode included highly aged traffic emission particles and biomass burning particles. The biomass burning particles had a larger rBC core (∼ 80–130 nm) and a thick ACT (∼ 110–300 nm). The highly aged traffic emissions had a smaller core (∼ 60–80 nm) and a very thick ACT (∼ 130–300 nm), which is larger than reported in any previous literature. A fast growth rate (∼ 20 nm h−1) of rBC with small core sizes was observed during the experiment. High concentrations pollutants like NO2 likely accelerated the aging process and resulted in a continuous size growth of rBC-containing particles from traffic emission.

Process analysis of a regional air pollution episode over Pearl River Delta Region, China, using the MM5-CMAQ model

This study focuses on the influences of a warm high-pressure meteorological system on aerosol pollutants, employing the simulations by the Models-3/CMAQ system and the observations collected during October 10–12, 2004, over the Pearl River Delta (PRD) region. The results show that the spatial distributions of air pollutants are generally circular near Guangzhou and Foshan, which are cities with high emissions rates. The primary pollutant is particulate matter (PM) over the PRD. MM5 shows reasonable performance for major meteorological variables (i.e., temperature, relative humidity, wind direction) with normalized mean biases (NMB) of 4.5–38.8% and for their time series. CMAQ can capture one peak of all air pollutant concentrations on October 11, but misses other peaks. The CMAQ model systematically underpredicts the mass concentrations of all air pollutants. Compared with chemical observations, SO2 and O3 are predicted well with a correlation coefficient of 0.70 and 0.65. PM2.5 and NO are significantly underpredicted with an NMB of 43% and 90%, respectively. The process analysis results show that the emission, dry deposition, horizontal transport, and vertical transport are four main processes affecting air pollutants. The contributions of each physical process are different for the various pollutants. The most important process for PM10 is dry deposition, and for NOx it is transport. The contributions of horizontal and vertical transport processes vary during the period, but these two processes mostly contribute to the removal of air pollutants at Guangzhou city, whose emissions are high. For this high-pressure case, the contributions of the various processes show high correlations in cities with the similar geographical attributes. According to the statistical results, cities in the PRD region are divided into four groups with different features. The contributions from local and nonlocal emission sources are discussed in different groups.Implications: The characteristics of aerosol pollution episodes are intensively studied in this work using the high-resolution modeling system MM5/SMOKE/CMAQ, with special efforts on examining the contributions of different physical and chemical processes to air concentrations for each city over the PRD region by a process analysis method, so as to provide a scientific basis for understanding the formation mechanism of regional aerosol pollution under the high-pressure system over PRD.

Influence of air quality on the composition of microbial pathogens in fresh rainwater.

In this study, the microbiological quality of fresh rainwater was assessed from 50 rain events under tropical weather conditions for a year. The levels of four major opportunistic waterborne pathogens, namely, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Aeromonas hydrophila, in rainwater samples were quantified by using a robust and sensitive quantitative PCR (qPCR) method. Of the 50 rainwater samples, 25 were found to be positive for at least one pathogen: 21 for E. coli, 16 for P. aeruginosa, 6 for K. pneumoniae, and 1 for A. hydrophila. In addition to the microbiological assessment of rainwater samples, we also studied the influence of prevailing air quality on the microbial quality of rainwater over the sampling period. A significant change in the diversity and relative abundance of the basic microbial indicator organisms in rainwater was observed during a major regional air pollution episode in Southeast Asia due to biomass-burning emissions.

Impact of Chinese Megacity Emissions on Regional Air Pollution Episodes in the Kyushu Area during Winter

Impact of Chinese Megacity Emissions on Regional Air Pollution Episodes in the Kyushu Area during Winter

Indonesian peat and vegetation fire emissions: Study on factors influencing large-scale smoke haze pollution using a regional atmospheric chemistry model

Numerical modelling of fire-related smoke haze episodes in Southeast Asia is important for both prediction and assessment of atmospheric impacts, especially when observational data are fragmentary, as is the case in Indonesia. This work describes the atmospheric fate of smoke particles emitted during the 1997 Indonesian fires modelled with a regional atmospheric chemistry model. We established a new fire emission inventory and calculate that 55 teragram (Tg) of particulate matter and 1098 Tg of carbon were released during this fire episode. Our emission estimate is an intermediate value compared with other studies. Utilising different scenarios, we demonstrate the variable atmospheric impacts of surface vegetation fires and peat soil fires separately and also investigate the sensitivity of smoke dispersion to the differing meteorological conditions of an El Nino and a normal year. When peat fires are included in the emission inventory, modelled ambient particle concentrations exceed the ambient air quality standard across transboundary scales. In a scenario including only surface vegetation fires, ambient air quality standards are exceeded only in areas close to the main fires. This scenario demonstrates the prominent role of fires in peat areas in causing regional air pollution episodes. In years with normal meteorological conditions, intermittent precipitation and associated wet deposition during the dry season are predicted to remove most of the particulate emissions close to the sources. Strongly reduced rainfall and generally stronger southeasterly winds during El Nino years provide favourable conditions for larger scale smoke haze pollution.

Effects of future climate change on regional air pollution episodes in the United States

We examine the impact of future climate change on regional air pollution meteorology in the United States by conducting a transient climate change (1950–2052) simulation in a general circulation model (GCM) of the Goddard Institute of Space Studies (GISS). We include in the GCM two tracers of anthropogenic pollution, combustion carbon monoxide (COt) and black carbon (BCt). Sources of both tracers and the loss frequency of COt are held constant in time, while wet deposition of BCt responds to the changing climate. Results show that the severity and duration of summertime regional pollution episodes in the midwestern and northeastern United States increase significantly relative to present. Pollutant concentrations during these episodes increase by 5–10% and the mean episode duration increases from 2 to 3–4 days. These increases appear to be driven by a decline in the frequency of mid‐latitude cyclones tracking across southern Canada. The cold fronts associated with these cyclones are known to provide the main mechanism for ventilation of the midwestern and northeastern United States. Mid‐latitude cyclone frequency is expected to decrease in a warmer climate; such a decrease is already apparent in long‐term observations. Mixing depths over the midwest and northeast increase by 100–240 m in our future‐climate simulation, not enough to compensate for the increased stagnation resulting from reduced cyclone frequency.