Fog is an important indicator of weather. Long-term variations of fog and mist were studied byanalyzing the meteorological data from 743 surface weather stations in China's Mainland during 1951-2005.In climatology, there are more foggy days in the southeast than in the northwest China and more in thewinter half of the year than in the summer half. The decadal change of foggy days shows regional variation.Southwest China is the region with the most foggy days, and more than 20 foggy days occur in SichuanBasin in one year. Persistent heavy fog usually appears in winter and spring over the North China Plain andNortheast China Plain. Misty days are much more frequent in the provinces south of the Yangtze River thanin the regions north of it, and there is an obvious increase of misty days after the 1980s. Southwest China isthe area with the most number of misty days, and more than 100 misty days occur in Sichuan Basin in ayear.
Our analysis of the surface aerosol and ultraviolet(UV) measurements in Pearl River Delta(PRD) region shows that the sur-face UV radiation is reduced by more than 50% due to high aerosol concentrations.This has important impacts on urban eco-system and photochemistry,especially on ozone photochemical production over the region.The quantitative effect of aerosols on surface ozone is evaluated by analyzing surface observations(including ozone,ultraviolet radiation,aerosol radiative pa-rameters) and by using radiative and chemical models.A case study shows that the aerosol concentrations and UV radiation are significantly correlated with ozone concentrations.The correlation coefficient between the aerosol optical depth(AOD) and the PM10 mass concentration is very high,with a maximum of 0.98,and the AOD and UV radiation/ozone is anti-correlated,with a correlation coefficient of -0.90.The analysis suggests that ozone productivity is significantly decreased due to the reduction of UV radiation.The noon-time ozone maximum is considerably depressed when AOD is 0.6,and is further decreased when AOD is up to 1.2 due to the reduction of ozone photochemical productivity.Because the occurring probability of aerosol optical depth for AOD550 nm≥0.6 and AOD340 nm≥1.0 is 47,and 55% respectively during the dry season(October,November,December,January),this heavy aerosol condition explains the low ozone maximum that often occurs in the dry season over the Guangzhou region.The analysis also suggests that the value of single scattering albedo(SSA) is very sensitive to the aerosol radiative effect when the radiative and chemical models are applied,implying that the value of SSA needs to be carefully studied when the models are used in calculating ozone production.
DENG XueJiaoZHOU XiuJiWU DuiTIE XueXiTAN HaoBoLI FeiBI XueYanDENG TaoJIANG DeHai
Samples of fog water collected in the area of Guangzhou during February, March and April of 2005 are used in this work to study the chemical composition of fog water in polluting fog there. Three typical episodes of polluting fog are analyzed in terms of ionic concentration and their possible sources. It is found that the concentration of various ions in fog water is much higher than those in rainwater. Fog not only blocks visual range but contains liquid particles that result in high degree of pollution and are very harmful to human health. SO4= is the anion with the highest concentration in fog water, followed by NO3-. For the cation, Ca++ and NH4+ are the highest in concentration. It is then known that rainwater is more acidic than fog water, indicating that ionic concentration of fog water is much higher than that of rainwater, but there are much more buffering materials in fog water, like NH4+ and Ca++. There is significant enrichment of Ca++, SO4=, and Mg++ in fog water. In the Guangzhou area, fog water from polluting fog is mainly influenced continental environment and human activity. The episodes of serious fog pollution during the time have immediate relationships with the presence of abundant water vapor and large amount of polluting aerosol particles.
