[Ozone Pollution Characteristics and Formation Mechanism in a Typical Tropical Seaside City].

To investigate the pollution characteristics and formation mechanism of ambient air ozone(O3) in a typical tropical seaside city, we conducted an observational experiment on O3 and its precursors at an urban site in Haikou, Hainan Province, from June to October 2019. The O3 pollution characteristics were analyzed comprehensively; the O3-NOx-VOCs sensitivities and key precursors were determined, and the control strategies for O3 pollution were carried out. The results were as follows:1 O3 pollution in Haikou mainly occurred in September and October, with daily maximum 8-h O3 concentrations in the range of 39-190 µg·m-3, and the daily variation in O3 was unimodal, peaking at approximately 14:00. 2 The concentrations of NO2 and VOCs were higher during O3 pollution episodes than their respective mean values in Haikou City. The increased O3 precursor concentrations were an important factor leading to O3 pollution, whereas O3 pollution was also influenced by regional transport, with pollutants mainly transported from the northeastern part of Haikou City. 3 O3-NOx-VOCs sensitivity in Haikou City was in the VOCs and NOx transitional regime, and the most sensitive precursors in various months were different. O3 formation in September was sensitive to anthropogenic VOCs the most; however, in October it was sensitive to NOx. 4 In the future, the reduction ratio of VOCs to NOx should be 1:1-4:1 to control O3 pollution effectively in Haikou.

[Spatial and Temporal Variations in Ozone Pollution and Sensitivity Characteristics in Hainan Island].

Based on ambient air quality data, meteorological observation data, and satellite remote sensing data, the temporal and spatial variations in ozone (O3) pollution, the sensitivity of O3, and its relationship with meteorological factors in Hainan Island were analyzed in this study. The results showed that the maximum daily 8-h moving mean (O3-8h) in western and northern cities in Hainan Island was higher than that in the central, eastern, and southern cities. O3-8h was the highest in 2015, and O3-8h exceeding the standard proportion was the largest in 2019. In addition, O3-8h was positively correlated with average temperature (P<0.1), sunshine duration (P<0.01), total solar radiation (P<0.01), atmospheric pressure, and average wind speed and was negatively correlated with precipitation (P<0.05) and relative humidity. The satellite remote sensing data showed that the tropospheric NO2 column concentration (NO2-OMI) and HCHO column concentration (HCHO-OMI) displayed opposite trends in Hainan Island from 2015 to 2020. Compared with those in 2015, NO2-OMI increased by 7.74% and HCHO-OMI decreased by 10.2% in 2020. Moreover, Hainan Island belongs to the NOx control area, and the FNR value exhibited a fluctuating downward trend in the past 6 years, with a trend coefficient and climatic trend rate of -0.514 and -0.123 a-1, respectively. A strong correlation was observed between meteorological factors and the FNR value of Hainan Island.

[Effects of Tropical Cyclones on Ozone Pollution in Hainan Island].

Based on the 181 tropical cyclones data in the western North Pacific Ocean from 2015 to 2020, hourly ozone (O3) concentration data, and meteorological observation data of 18 cities and counties in Hainan Island, this study analyzed the impacts of tropical cyclones on ozone pollution in Hainan Island. We found that 40 (22.1%) tropical cyclones experienced O3 pollution in Hainan Island during the lifetime of tropical cyclones in the past six years. During the years with more tropical cyclones, more O3- polluted days occurred in Hainan Island. Highly polluted days, which were defined as more than or equal to three cities and counties exceeding the standard, were the most serious in 2019 with 39 (54.9%) polluted days. The tropical cyclones related to high pollution (HP) showed an increasing trend, with the trend coefficient and climatic trend rate of 0.725 (exceeding the 95% significance level) and 0.667 a-1, respectively. Tropical cyclone intensity was positively correlated with the maximum 8 h moving average (O3-8h) concentration in Hainan Island. Among them, HP-type tropical cyclones accounted for 35.4% of all samples in the typhoon (TY) intensity level. Cluster analysis of tropical cyclone paths showed that tropical cyclones from the South China Sea (type A) were the most common of the 67 (37%) and were the most likely to cause large-scale and high-concentration O3 pollution events in Hainan Island. The average number of HP tropical cyclones and ρ(O3-8h) of Hainan Island in type A were 7 and 121.90 µg·m-3, respectively. In addition, the tropical cyclone centers were located generally in the middle part of the South China Sea and the western Pacific Ocean near the Bashi Strait during the HP period. The change in meteorological conditions in Hainan Island under the influence of HP tropical cyclones was conducive to the increase in O3 concentration.

[Influence of Typhoon Nangka Process on Ozone Pollution in Hainan Island].

In order to explore the influence of the 2016 typhoon Nangka on ozone (O3) concentration in Hainan Island, this study employed correlation analysis and backward trajectory simulated methods, using the hourly air quality monitoring data, meteorological data, EAR5 reanalysis data, and bright temperature (TBB) infrared from the Himawari-8 satellite from October 10 to 14, 2020. The results showed that, during the typhoon process from October 11 to 13, the O3-8h (maximum of 8 hours sliding average) concentration exceeded the standard. The averaged ρ(O3-8h) of Hainan Island reached its peak value (130.5 µg·m-3) in October 12, 2020, with the O3-8h concentration exceeding the standard in four cities and counties, in which Lingao County reached the highest concentration of 198.44 µg·m-3. During the typhoon process, the hourly O3 concentration was negatively correlated with precipitation, relative humidity, and wind speed and positively correlated with air pressure and air temperature. Moreover, the correlation coefficients between O3 with precipitation, air pressure, and relative humidity exceeded the 99.9% confidence level. The southeastern coastal provinces of China were the main contribution source area for this ozone pollution process on Hainan Island. Affected by the downdraft inside the western Pacific subtropical high (WPSH) and the downdraft outside the circumference of typhoon Nangka, vertical transport in the atmosphere appeared over the contribution source area. The meteorological conditions were favorable for atmospheric photochemical reactions. Air pollutants were transported to Hainan Island along the northeast airflow around the typhoon, resulting in the occurrence of an O3 pollution event. In addition, this study built a weather conceptual model of O3 pollution in Hainan Island affected by typhoon Nangka, which can be used as a reference for the joint pollution prevention and control by air pollution prediction, early warning, and environmental management departments.

[Characteristics and Potential Sources of Four Ozone Pollution Processes in Hainan Province in Autumn of 2019].

Based on the air quality and meteorological monitoring data of Hainan province in autumn of 2019, this study analyzed the characteristics and potential sources for the four O3 polluted processes in Hainan province, using the methods of correlation analysis, HYSPLIT backward trajectory modeling, PSCF (potential source contribution function), and CWT (concentration weighted-trajectory). The results showed that ① the average concentrations of the maximum 8h average (O3-8h) for process 1 and process 3, which occurred from September 21st to 30th and November 3rd to 11th with the durations of 10 d and 9 d, were 145.52 µg·m-3 and 143.55 µg·m-3, respectively. Process 2 and process 4 occurred from October 18th to 21st and November 20th to 25th, with the durations of 4 d and 6 d, and the average concentrations of O3-8h were 130.79 µg·m-3 and 115.46 µg·m-3, respectively. ② High air pressure, low precipitation and relative humidity, long sunshine duration, and strong solar radiation favored the occurrence of O3-polluted weather in Hainan province. Northerly wind was conducive to the increase in O3-8h concentration, and wind speeds affected the regional distribution of high-value areas of O3-8h concentration in Hainan province. ③ Furthermore, process 1 and process 3 with more serious pollution had a larger air flow divergence, and there were two airflows originating from the inland area and the southeast coastal area, respectively. Air flow of process 2 and process 4 was relatively more concentrated with less O3 pollution and was classified as southeast coastal air flow. 4 The analysis of potential contribution sources showed that transport from Zhejiang, Jiangxi, Fujian, and Guangdong provinces were the main sources of O3 pollution in Hainan province in autumn 2019. Among them, the weight potential source contribution function (WPSCF) and weight concentration weighted-trajectory (WCWT) values were larger than 0.36 and 90 µg·m-3 in the PRD (Pearl River Delta) and western Guangdong province regions, respectively.

[Temporal and Spatial Variations in Ozone and Its Causes over Hainan Province from 2015 to 2020].

This study investigated temporal and spatial variations in O3-8h (defined as the maximum 8 h average result) in Hainan Province from 2015 to 2020 and further analyzed its relationships with precursors and meteorological factors based on a dataset of observations from 32 environmental monitoring stations in Hainan. Basic statistical methods, including the empirical orthogonal function (EOF), climatic tendency rate, and climatic trend coefficient analysis, were used here. The results showed that ρ(O3-8h) was higher in northern and western Hainan than that in other regions, with the maximum value occurring in Dongfang City (91.5 µg·m-3). Twelve cities and counties experienced a downward trend from 2015 to 2020, and six cities and counties reached a 95% confidence level. The variation in ρ(O3-8h) in Hainan Province demonstrated remarkable seasonal changes, which were the largest in the autumn, spring, and winter followed by the smallest in the summer, exhibiting a clear declining trend in all seasons except autumn. In addition, the cumulative variance of the first two eigenvector fields decomposed by EOF was 72.58%, which could well describe the distributed characteristics of ρ(O3-8h) in Hainan Province. The first mode reflected the consistency of ρ(O3-8h) variation, and the second mode reflected regional differences. Meanwhile, the change in ρ(O3-8h) had a good correlation with the precursors and meteorological factors. Among them, the correlation coefficients between ρ(O3-8h) and ρ(NO2), precipitation, sunshine duration, average temperature, average wind speed, atmospheric pressure, and total radiation passed the 99% confidence test. The results of multiple linear regression showed that the variation in regressed ρ(O3-8h) was consistent with the observed ρ(O3-8h), and the correlation coefficient between them was 0.853, which passed the 99.9% confidence test. The regression value explained 0.72 variance of the observed value.

Influence of early thermal-oxidative ageing on the structure and properties of polyoxymethylene copolymer.

Thermal-oxidative ageing of polyoxymethylene (POM) copolymer in the oven at 100°C for 1, 2, 3, 5, 7, 10, 14 and 21 days and the influence of early thermal-oxidative ageing on POM structure and properties were studied by means of wide-angle X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry and tensile test. Based on the results, we found that the early thermal-oxidative ageing of POM copolymer can be divided into three regions. The region I is the initial 3 days. In this region, some molecular chains rearranged, resulting in internal stress relaxation, increase of crystallinity degree and grain size due to the perfection of crystal structure; both extended chain crystal (ECC) and folded chain crystal (FCC) increased and ECC grew faster than FCC. The region II is from 3 days to 10 days, and in this region, chain scission took place in amorphous region and led to chemi-crystallization. The region III is after 10 days. In this region, the structure and performance of POM copolymer reached a stable situation at this stage. In this work, the difference between skin and core were also analysed.

[Formation Mechanism of a Serious Pollution Event in January 2013 in Beijing].

The weather conditions, atmospheric environmental background and formation mechanism of a heavy air pollution episode in Beijing City from January 9th to 15th, 2013 was preliminarily investigated by combining observed data and the WRF meteorology model. The results showed that the average concentration of PM2.5 was 323 µg x m(-3) from January 10th to 14th; the heavy pollution episode was closely related to the local meteorological conditions; the stable atmospheric circulation pattern provided favorable environmental field for the lasting of this heavy air pollution; small wind speed, high humidity, low PBL, and lasting temperature inversion were the main reasons for this heavy air pollution incident; further analysis showed that contributions of regional transmission to the receptor sites in Beijing were between 53% - 69% and there were obvious secondary conversions and transformations; overall regional transportation played a more important role during this serious air pollution incident; the meteorological conditions played a key role in the formation and destruction of the heavy air pollution, therefore we need to strengthen the study on early warning of heavy air pollution, in order to prevent and control the air heavy pollution effectively.