SPATIOTEMPORAL VARIATION OF NO2 AND SUB-REGIONAL TRANSPORT DURING WINTER POLLUTION EVENTS IN HAIKOU, CHINA

An ensemble of satellite measurements, statistic data from government and meteorological diagnosis in regional background site (Haikou, China) has revealed the spatial and temporal characteristics of NO2 and associated synoptic transport patterns over southern China from January 2013 to February 2014. The result shows that: (1) Ozone Monitoring Instrument (OMI) satellite products had a good correlation with observation NO2 in Haikou. The correlation coefficients between Observation NO2 and tropospheric column NO2 and ratio of TroNO2/ TotNO2(tropospheric column NO2/ total column NO2) had all passed the confidence level of 99.9% test. (2) TroNO2 over southern China has an obvious seasonal variation, which is closely coupled with regional meteorology in each season. (3) NO2 concentration in Haikou revealed three pollution periods during December 2013 and January 2014. The variation of NO2 concentration in Haikou is related to the meteorological elements closely. (4) Compared to the monthly mean meteorological fields of the pollution periods, the results indicate that NO2 pollution event in Haikou is directly related to the exogenous transportation from PRD region. An ensemble analysis of meteorological dynamic factors, wind vectors and backward trajectories during the pollution periods further verified this conclusion.     

重污染下华南地区小雨和低云量的时空变化趋势特征

利用华南地区51个站点的逐日小雨降水和低云量等气象资料,采用气候趋势系数、一元回归和相关分析等方法,分析了小雨降水和低云量的年际、季节的长期趋势特征,同时结合华南地区气溶胶光学厚度(AOD)、气溶胶指数和国民生产总值(GDP)等资料进行原因探讨。(1) 华南地区小雨日和低云量呈相反的变化趋势(小雨日下降,低云量上升),而且表现为东部高于西部,沿海高于内陆的分布特征。(2) 小雨日和低云量的回归系数分别为-4.88 d/(10 a)和1.17%/(10 a)。(3) 春季和夏季小雨日变化相对较小,但是对年小雨日贡献较大,而低云量四季均呈现相反的上升趋势。(4) 华南地区的两个AOD大值区分别位于广西中部到南部沿海和广东珠三角地区,其中珠三角地区AOD高达0.7以上,气溶胶指数也表现为沿海地区高于内陆地区的分布特征。近27年华南地区的气溶胶指数呈现波动的上升趋势,与同期的小雨日呈负相关关系,而低云量呈正相关关系,近28年华南地区GDP一直处于明显上升趋势,其中以广东省增加最明显。      

Long-Term Trends in the Probability of Different Grades of Haze Days in China from 1960 to 2013

The number of haze days and daily visibility data for 543 stations in China were used to define the probabilities of four grades of haze days: slight haze(SLH) days; light haze(LIH) days; moderate haze(MOH) days; and severe haze(SEH) days. The change trends of the four grades of haze were investigated and the following results were obtained. The highest probability was obtained for SLH days(95.138%), which showed a decreasing trend over the last54 years with the fastest rate of decrease of-0.903% ·(10 years)-1 and a trend coefficient of-0.699, passing the 99.9%confidence level. The probabilities of LIH and MOH days increased steadily, whereas the probability of SEH days showed a slight downward trend during that period. The increasing probability of SLH days was mainly distributed to the east of 105°E and the south of 42°N and the highest value of the trend coefficient was located in the Pearl River Delta and Yangtze River Delta regions. The increasing probability of LIH days was mainly distributed in eastern China and the southeastern coastal region. The probabilities of MOH and SEH days was similar to the probability of LIH days. An analysis of the four grades of haze days in cities with different sizes suggested that the probability of SLH days in large cities and medium cities clearly decreased during the last 54 years. However, the probabilities of LIH days was 10% and increased steadily. The probability of MOH days showed a clear interdecadal fluctuation and the probability of SEH days showed a weak upward trend. The probability of SLH days in small cities within 0.8° of large or medium cities decreased steadily, but the probability of LIH and MOH days clearly increased, which might be attributed to the impact of large and medium cities. The probability of SLH days in small cities 1.5° from a large or medium city showed an increasing trend and reached 100% after 1990; the probability of the other three grades was small and decreased significantly.     

THE SPATIOTEMPORAL CHARACTERISTICS OF LIGHT RAIN DAYS AND LOW CLOUD COVER UNDER HEAVY POLLUTION OVER SOUTH CHINA

By using the data set of light rain days and low cloud cover at 51 stations in South China (SC), and the method of linear regression and correlative analysis, we analyze the spatiotemporal characteristics of the light rain days and low cloud cover including annual variation and long-term seasonal change. The results are as follows: (1) The trends of light rain days and low cloud cover over SC are opposite (light rain days tended to decrease and low cloud cover tended to increase in the past 46 years). The value distributed in east is higher than that in west, and coastal area higher than inland area. (2) The regression coefficients of light rain days and low cloud cover during 1960–2005 are 4.88 d/10 years and 1.14%/10 years respectively, which had all passed the 0.001 significance level. (3) Variations of light rain days are relatively small in spring and summer, but their contributions are larger for annual value than that of autumn and winter. (4) There are two regions with large values of aerosol optical depth (AOD), which distribute in central and southern Guangxi and Pearl River Delta (PRD) of Guangdong, and the value of AOD in PRD is up to 0.7. The aerosol index distributed in coastal area is higher than in the inland area, which is similar to the light rain days and low cloud cover over SC. Aerosol indexes in SC kept increasing with fluctuation during the past 27 years. The GDP of the three provinces in SC increased obviously during the past 28 years, especially in Guangdong, which exhibited that there is simultaneous correlation between light rain days with the variables of low cloud cover and release of aerosols over SC during 1960 to 2005.