| Dust events occur frequently in arid and semi-arid regions of the northern China, which do not only severely damage local industrial and agricultural production and eco-environment but also transfer a large amount of dust particles long distance. Thus, they can deteriorate atmospheric environment and harm human health in downstream areas such as Northern China and Japan as major floating pollution source, which have drawn high attention of relevant scientists and people. So, some aspects of dust events have been monitorted and studied in this paper. Firstly, the general impacts on the urban atmospheric environment of Northern China and Japan are discussed.Then, the impact on the atmospheric environment and water-soluble ions in Lanzhou city is quantitatively analyzed, which is seriously affected by dust events. Finally, the influence levels of dust events on the PM10concentrations of seven cities in neighboring Japan are studied. Moreover, as example of Menzenmaqi in Japan, the impact of dust events on water soluble ions in PM10in Japan is comprehensively investigated. The main conclusions are summarized as follows:(1) The impacts of dust events on air qualities in the nine cities in Northern China are analyzed by using the air pollution index (API) data during2006-2010from the Ministry of Environmental Protection of the People’s Republic of China and the observation data of dust events from Meteorological Observation Stations.The results show that the synoptic processes of blowing sand, dust storm and severe dust storm in China have taken place during2006-2010. The intensity of dust events is very strong in2006, which is relatively weak in2009. In addition, the frequency of dust events in2009is low. Northwest route is the most frequent transport route of dust events in China in this study. PM10is the main air pollutant in the nine cities, and its frequency is high as the primary air pollutan, especially in spring when dust events are apt to occur. Air qualities in these cities are all affected by dust events, and the influence levels are different, on the whole, the impacts on the urban air qualities in sand source are serious, and the impacts on the urban air qualities in affected regions decrease far from sand source according to geographic position, which reveals that the impact of dust events on the urban air quality in northern China presents regional characteristics.(2) Characteristics of dust events in Lanzhou during1951-2010and the impact of dust events on atmospheric environment of Lanzhou are studied by using dust events data from Lanzhou Meteorological Observing Station and air pollutant data including PM10, SO2and NO2concentrations from Lanzhou Environmental Monitoring Station. The results show that floating dust, blowing dust and dust storm in Lanzhou have taken place during1951-2010. The most frequent occurring dust is floating dust, which is on average30.4days per year. Frequencies of three kinds of dust events generally descended from1954to2000. The impact of dust events on PM10concentration is serious in Lanzhou, the increase rate of PM10concentration in dust days compared with non-dust days in spring every year are between79%and343%. The highest increase rate is in the spring2007; resulting from the high intensity of dust events and low average PM10concentration in non-dust days.The impacts of dust events on PM2.5and PM1.0concentrations are both obvious; but the impacts of dust events on SO2and NO2concentrations are little. By analyzing carefully a severe dust event on May10,2007, it can be found that three diameter particles concentrations sharply increase with dust intrusion, then reach relatively high level, afterwards gradually drop and recover to the normal concentration level because of dust weakening, fading or leaving; in other words, when dust events invading, dust particles concentrations sharply increase, and after reaching the maximum value, they slowly drop.(3) A semi-continuous measurement of water-soluble ions in PM10and related gases in Lanzhou in the spring of2011is conducted by using Monitoring Instrument for Aerosols and Gases. Based on the measurement, the impacts of dust events and rain on water-soluble ions in PM10and related gases are analyzed. The results indicate that the gas pollutant and water-soluble ions in PM10with the maximum concentrations in this study are SO2and Ca2+respectively, and the average concentrations are5.87μg/m3and18.25μg/m3, which is apparently due to high coal consumption and frequent dust events in spring in Lanzhou. Concentrations of all gas pollutants and water-soluble ions in rain are lower than those before rain, gas HNO2and NO3-, SO42-in PM10can be more effectively wiped off by rain. Gas pollutant concentrations in dust events tend to decrease due to strong wind, while the concentrations of water-soluble ions in PM10increase, Ca2+concentration as the representative dust particle goes up most obviously. The characteristic of Ca2+concentration variation in dust events is similar to that of dust particles, i.e., Ca2+concentration sharply increases with dust event invading, then, keeps at relatively high level for quite a long time, finally, gradually drops and recovers to normal concentration level due to dust weakening, fading or leaving.(4) Characteristics of dust events in Japan during1967-2010and the impacts of dust events on the PM10concentrations in Japan are studied by the dust event data of the seven different geographical and type cities (Sapporo, Nonodake, Kawasaki, Nagoya, Osaka, Matsue, Omuta) from Japan Meteorological Agency and the PM10concentration data from the Ministry of Environmental Government of Japan. The results show that the PM10concentrations in seven cities have remarkable spatial variation, the average PM10concentrations of Osaka, Kawasaki and Nagoya are high, and the PM10concentrations of Nonodake and Sapporo are low. Due to different meteorological factors and air pollutant emission, average deviations of PM10concentrations in the seven cities have high variation and dispersion. The PM10concentration of dust days in7cities had increased due to the impact of dust events, but the intensity and absolute value were both low compared to Northern China, and the impact of dust events on the PM10concentration in Japan has regional discrepancy. The increase rates of PM10concentrations of dust days generally decrease from the west to the east, and reduce from low latitude to high latitude according to geography.(5) Characteristics of water-soluble ions in PM10at Menzenmaqi, Japan from2001to2003and the impact of dust events on them are investigated by backward air trajectory analysis and positive matrix factorization. The results show that SO42", NO3-and NH4+are the main water-soluble ions in PM10at Menzenmaqi, Japan from2001to2003; The average monthly concentrations of SO42-, NH4+, NO3-and nss-Ca2+have prominent peaks in spring due to strong influence of dust events, the average nss-Ca2+concentration in dust days drastically increases when dust events invade, which is0.86μg/m3, about three times higher than that in normal days. In addition, the average concentrations of nss-SO2-, NO3-and NH+/in dust days are higher than those in normal days, for the reason that dust particles adsorb SO2and NOx, and react with them during the long-range transport. By positive matrix factorization method, the major source profiles of PM10were categorized as dust source, marine salt, secondary sulfate and secondary nitrate. |
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