[Effects of Tropical Cyclones on Ozone Pollution in the Pearl River Delta in Autumn].

Based on the tropical cyclone track data in the northwest Pacific Ocean from 2015 to 2020, meteorological observation data, and ozone concentration monitoring data in the Pearl River Delta (PRD), the impacts of four tropical cyclones, namely the westbound tropical cyclone (type A), East China Sea tropical cyclone (type B), offshore tropical cyclone (type C), and offshore tropical cyclone (type D), on ozone concentration in the PRD were analyzed. The results showed that:under the influence of the type A tropical cyclone, the risk of regional ozone concentration exceeding the standard exhibited little change. Under the influence of the type B tropical cyclone, the risk of ozone exceeding the standard in the PRD was obviously increased. Under the influence of the type C tropical cyclone, the risk of regional ozone exceeding the standard obviously increased, but the increase was weaker than that of the type B tropical cyclone. The type D tropical cyclone was far away from the Chinese mainland and had little influence on ozone concentration in the PRD. When the type A or type C tropical cyclones occurred, the average daily maximum 8-hour average ozone concentration (MDA8) in the PRD region increased by approximately 5 µg·m-3, and the ozone MDA8 in some cities may have decreased. When the type B tropical cyclone occurred, the regional ozone MDA8 increased by 19 µg·m-3 on average, and the ozone concentration in all cities increased significantly. Among them, the average increase in ozone MDA8 in Zhuhai and Jiangmen was relatively large, with an increase of greater than 20 µg·m-3. Generally speaking, the ozone concentration in cities in the western PRD was more affected by tropical cyclones. When the type B tropical cyclone occurred, solar radiation increased, sunshine duration lengthened, cloud cover decreased, air temperature rose, and relative humidity decreased in the PRD, all of which were beneficial to photochemical reactions. Meanwhile, downward flow increased in the boundary layer, and downward flow transported high-concentration ozone to the ground, which promoted the increase in ozone concentration on the ground. When type A or type C tropical cyclones occurred, the change in meteorological conditions was not entirely conducive to the increase in ozone concentration, and in some cases, even adverse meteorological conditions such as rainfall occurred, which led to the risk of regional ozone exceeding the standard being less than that of the type B tropical cyclone. Affected by tropical cyclones, sunshine hours and air temperature in western cities of the PRD increased more than those in eastern cities, which was more conducive to ozone generation.

[Ozone Pollution Trend in the Pearl River Delta Region During 2006-2019].

Based on the monitoring data of the Guangdong-Hong Kong-Macao Pearl River Delta Regional (PRD) Air Quality Monitoring Network from 2006 to 2019, the ozone trend in RRD was analyzed using the Mann-Kendall test method, Sen's slope method, and the Pettitt change point test. The results show that:① the average ozone concentration in the PRD has increased significantly from 2006 to 2019 (P<0.05), with an average growth rate of 0.80 µg·(m3·a)-1. After 2016, the rate of ozone increase has accelerated. ② The average annual ozone concentration in the central PRD increased significantly, while in the peripheral areas of the PRD, this is not obvious. Ozone increases significantly in summer but not in other seasons.③ From 2006 to 2019, the concentration of NO2 in the central PRD decreased remarkably, so the titration effect weakened and resulted in an increase in the ozone concentration. The concentration of NO2 in the marginal areas of the PRD has little change, so the ozone concentration in these areas has little change. ④ With the changes of VOCs and NO2 concentrations, the chemical sensitivity of O3 production in the PRD is changing. The VOC-limited regimes are continuously decreasing, and the mixed NOx-VOC-limited regimes and NOx-limited regimes are increasing. In order to deal with regional ozone pollution, the cooperative control of VOCs and NOx needs to strengthen.

[Impact of Meteorological Factors on the Ozone Pollution in Hong Kong].

Based on ozone monitoring and meteorological data from 2000 to 2015 in Hong Kong, the characteristics of ozone pollution and the influence of meteorological factors on the ozone pollution were analyzed. The results show that:① A seasonal variation of the ozone concentration in Hong Kong is notable:autumn > spring > winter > summer. Days of ozone exceeding the standard value are concentrated in summer and autumn and rarely occur in winter and spring. ② The annual mean ozone concentration of the maximum daily 8-h average (MDA8) in Hong Kong increases from 2000 to 2015, with an average growth rate of 0.77 µg·(m3·a)-1. The 90th percentile concentration of the ozone MDA8 also increases, with an average rate of 1.49 µg·(m3·a)-1. ③ Higher temperatures are necessary for ozone pollution in Hong Kong. The higher the temperature is, the more ozone pollution likely occurs. ④ In most cases, the ozone concentration is negatively correlated with the relative humidity. The higher the relative humidity is, the lower are the ozone and 90th percentile concentrations in Hong Kong. ⑤ When ozone pollution occurs in Hong Kong, prevailing winds tend to shift from northerly or easterly to westerly. In addition, with the increase of the wind speed, the average ozone concentration changes little, but the 90th percentile ozone concentration significantly decreases. ⑥ Precipitation and cloud cover are important factors affecting the ozone concentration. Weather conditions without or with little rain for many consecutive days are necessary for the occurrence of ozone pollution events. However, with the increase of the cloud cover, the average ozone and 90th percentile concentrations continue to decrease. ⑦ In the case of a total solar radiation ≤ 20 MJ·m-2 or sunshine duration ≤ 10 h, the ozone concentration is positively correlated with the solar radiation and sunshine duration. However, in the case of intense solar radiation (total solar radiation>20 MJ·m-2 or duration of sunshine>10 h), the ozone concentrations decrease with increasing solar radiation or duration because strong solar radiation often occurs in the background of sunny weather after rain. At the same time, southerly winds from the sea often prevail, making it difficult for ozone pollution to occur in Hong Kong. ⑧ Ozone excess days in Hong Kong are often accompanied by changes of a series of meteorological conditions including less rain on sunny days, stronger radiation, higher boundary layer height, lower relative humidity, smaller wind speeds, and higher temperatures. The end of the pollution process is accompanied by the opposite weather changes.

[Influence of Burning Fireworks on Air Quality During the Spring Festival in the Pearl River Delta].

Based on data from the air quality monitoring stations in the Pearl River Delta during the 2015 Spring Festival, the regional air quality was investigated and the impact of burning fireworks on urban air quality was assessed. The results showed that: Zhaoqing was the worst polluted city in PM10, PM2.5, SO2 and CO in terms of concentrations in the region during the period, Huizhou was the worst polluted city in O3 and Guangzhou was the most polluted city in NO2 at the same time. Compared to the data of last year, the SO2, NO2, CO, PM10 and PM2.5 concentrations had decreased significantly, but the O3 concentration had increased during the Spring Festival. Burning fireworks during the Spring Festival were mainly concentrated in the suburbs. The concentrated discharge of fireworks made the SO2, PM10 and PM2.5 concentrations increased significantly in the New Year's Eve night, even multiplied, but had no significant effect on CO, O3 and NO2. The rapid decline in PM2.5/PM10 proportion was caused by the discharge of fireworks, and the ratio of PM2.5/PM10 reached the minimum when concentration of particles reached the peak. By assessing, the maximum contribution of hourly concentration from burning fireworks in each city was between 16 µg · m⁻³ and 65 µg · m⁻³ for PM2.5, between 28 µg · m⁻³ and 138 µg · m⁻³ for PM10 and between 9 µg · m⁻³ and 43 µg · m⁻³ for SO2.

[Distribution of Regional Pollution and the Characteristics of Vertical Wind Field in the Pearl River Delta].

Based on the data of hourly PM2.5 concentration of 56 environmental monitoring stations and 9 cities over the Pearl River Delta (PRD) region, the distributions of PM2.5 pollution in PRD region were analyzed by systematic cluster analysis and correlational analysis. It was found that the regional pollution could be divided into 3 types. The first type was the pollution occurred in Dongguan, Guangzhou, Foshan and Jiangmen (I type), and the second type was the pollution occurred in Zhongshan, Zhuhai, Shenzhen and Huizhou (II type), while the last type was the pollution only occurred in Zhaoqing (III type). During the study period, they occurred 47, 7 and 128 days, respectively. During events of pollution type I, except Zhuhai, Shenzhen and Huizhou, the PM2.5 concentrations of other cities were generally high, while the PM2.5 concentration in whole PRD region was over 50.0 µg x m(-3) during events of pollution type II. The regions with higher PM2.5 concentration was mainly concentrated in Zhaoqing, Guangzhou and Foshan during events of pollution type III. The wind data from 4 wind profile radars located in PRD region was used to study the characteristics of vertical wind field of these 3 pollution types. It was found that the wind profiles of type I and III were similar that low layer and high layer were controlled by the southeast wind and the southwest wind, respectively. For type II, the low layer and high layer were influenced by northerly wind and westerly wind, respectively. Compared with other types, the wind speed and ventilation index of type II. were much higher, and the variation of wind direction at lower-middle-layer was much smaller. When PRD region was influenced by northerly winds, the PM2.5 concentration in the entire PRD region was higher. When PRD region was controlled by southeast wind, the PM2.5 concentrations of I and II areas were relatively lower, while the pollution in III area was relatively heavier.

[Uncertainty analysis of ecological risk assessment caused by heavy-metals deposition from MSWI emission].

The CALPUFF model was applied to simulate the ground-level atmospheric concentrations of Pb and Cd from municipal solid waste incineration (MSWI) plants, and the soil concentration model was used to estimate soil concentration increments after atmospheric deposition based on Monte Carlo simulation, then ecological risk assessment was conducted by the potential ecological risk index method. The results showed that the largest atmospheric concentrations of Pb and Cd were 5.59 x 109-3) microg x m(-3) and 5.57 x 10(-4) microg x m(-3), respectively, while the maxima of soil concentration incremental medium of Pb and Cd were 2.26 mg x kg(-1) and 0.21 mg x kg(-1), respectively; High risk areas were located next to the incinerators, Cd contributed the most to the ecological risk, and Pb was basically free of pollution risk; Higher ecological hazard level was predicted at the most polluted point in urban areas with a 55.30% probability, while in rural areas, the most polluted point was assessed to moderate ecological hazard level with a 72.92% probability. In addition, sensitivity analysis of calculation parameters in the soil concentration model was conducted, which showed the simulated results of urban and rural area were most sensitive to soil mix depth and dry deposition rate, respectively.

[Characteristic analysis of a multi-day pollution event in Chang-Zhu-Tan Metropolitan Area during October 2013].

Chang-Zhu-Tan Metropolitan Area experienced a typical multi-day pollution event in October 2013. Based on the air pollution index, conventional pollutants observations, surface meteorological observations and sounding data, the relationships of air pollution, large-scale circumfluence and boundary layer meteorology of this event were comprehensively analyzed. Additionally, the sources and transport paths of pollutions were investigated by application of satellite remote sensing data and HYSPLIT4 model. The results showed that pollutants gradually accumulated in the earlier stage of the event (October 21th to 26th) , while in the later stage (October 27th to 31th) the characteristic pollutants of crop residue burning (PM2.5, CO, NO2) sharply increased. The deterioration of air quality in the later stage was mainly related to the remote transport of pollutants caused by straw burning. Analysis of simulations of HYSPLIT4 model and fire spots showed that the currents mainly came from Anhui and Hubei Province in the earlier stage, while in the later stage they were mainly from Jiangxi Province where fire spots were intensively located. Stable atmospheric stratification caused by steady uniform high-pressure field and slight wind due to the confrontation of cold and warm currents greatly contributed to the development, maintainability and reinforcement of the pollution event. The remote transport of pollutants had a significant impact on ambient air quality of Chang-Zhu-Tan Metropolitan Area.

[Study on air quality and pollution meteorology conditions of Guangzhou during the 2010 Asian games].

Based on the monitoring data of NO2, O3, SO2, PM, visibility, regional air quality index (RAQI) and the atmospheric transport and diffusion data from Nov. 4, 2010 to Dec. 10, 2010 in Guangzhou area, the variations of air quality and meteorological conditions during the Guangzhou Asian Games were analyzed. It was found that, during the Asian Games, the air quality was better than the air quality before or after the Asian Games. The visibility was greater than the visibility before or after the Asian Games, while the concentrations of PM1 and PM2.5 were lower. The correlation coefficient between visibility and the concentrations of PM1, PM2.5 indicated anti-correlation relationships. Daily and hourly concentrations of NO2 and SO2 met the primary ambient air quality standards, whereas the daily concentration of PM10 and hourly concentration of O3 met the secondary ambient air quality standards. Pollutants had been well controlled during the Asian Games. The concentration of SO2 in Guangzhou was influenced by local sources and long distance transmission, while the concentration of NO2 was significantly influenced by local sources. The emissions of NO2, SO2 and PM10 surrounding Guangzhou had a trend to affect the concentrations in Guangzhou, but the situation of O3 was opposite, the relatively high concentration of O3 in Guangzhou had tendency to be transported to the surrounding areas. The pollution meteorology conditions in the period of Asian Games were better than the conditions before or after the Asian Games. The decrease in the concentrations during the Asian Games did not only benefit from the emission control by the government, but also from the good meteorological conditions.

Characteristics of indoor/outdoor PM2.5 and elemental components in generic urban, roadside and industrial plant areas of Guangzhou City, China.

Quantitative information on mass concentrations and other characteristics, such as spatial distribution, seasonal variation, indoor/outdoor (I/O) ratio, correlations and sources, of indoor and outdoor PM2.5 and elemental components in Guangzhou City were provided. Mass concentration of PM2.5 and elemental components were determined by standard weight method and proton-induced X-ray emission (PIXE) method. 18 elements were detected, the results showed positive results. Average indoor and outdoor PM2.5 concentrations in nine sites were in the range of 67.7-74.5 microg/m3 for summer period, and 109.9-123.7 microg/m3 for winter period, respectively. The sum of 18 elements average concentrations were 5362.6-5533.4 ng/m3 for summer period, and 8416.8-8900.6 ng/m3 for winter period, respectively. Average concentrations of PM2.5 and element components showed obvious spatial characteristic, that the concentrations in roadside area and in industrial plant area were higher than those in generic urban area. An obvious seasonal variation characteristic was found for PM2.5 and elemental components, that the concentrations in winter were higher than that in summer. The I/O ratio of PM2.5 and some elemental components presented larger than 1 sometimes. According to indoor/outdoor correlation of PM2.5 and element concentrations, it was found that there were often good relationships between indoor and outdoor concentrations. Enrichment factors were calculated to evaluate anthropogenic versus natural elements sources.