Analysis Of Environmental Factors In Yangtze Delta During Periods Of Haze And Non-haze In Shanghai

Shanghai and Yangtze River estuary are adjacent, and the former’s industrialization and urbanization has brought tremendous economic growth, but also exert great pressure on the ecological environment. It is known that Yangtze River Delta is ranked among the most serious regions in China. Especially in Shanghai, haze days have reached up to 192 days, and seriously affected the sustainable development of the Yangtze River Estuary. Fine particulate matter during haze days will enter the ocean ecosystem as atmospheric circulation. A part of them settles to the coastal waters directly, another part settles into the oligotrophic waters with long-distance transport and brings the ocean new productivity. The PM2.5 concentration of 10 environmental monitoring stations in Shanghai and the 23 environmental factors of 43 monitoring sites in Yangtze Delta were analyzed in haze and non-haze days, in order to analysis the influence of haze days on the marine ecosystem. This study compared the seasonal changes in haze and non-haze days, and found the correlations between PM2.5 and environmental factors in haze and non-haze days. This research could provide the necessary scientific basis for the study of the marine environment in haze days and the development of offshore aquaculture industry. The results are as follows:(1) 33 days’ PM2.5 concentrations were higher than 0.065μg/m3, of which 30 days were in winter, 3 days in spring. From the contamination level of haze, the severe haze occurred: winter>spring>summer>autumn; moderate haze occurred: spring>summer> winter >autumn; mild haze occurred: spring> autumn> summer=winter. Haze occurs in the spring frequently, but severely in winter.(2) Among 23 environmental factors, five environmental factors showed the same seasonal trends in haze and non-haze days: temperature(T), dissolved oxygen(DO), chemical oxygen demand(COD), active phosphate, total organic carbon(TOC), and their concentrations in haze days were lower than non-haze days, except the temperature(T) in spring. The concentrations of arsenic(As), active silicate, nitrate in haze days were also lower than non-haze days. But salinity in haze days was higher than non-haze days. Suspended solids maintained a high concentration year-round, were greatly influenced by the input of Yangtze River runoff, besides, they would diffuse to open sea in summer and winter. No significant trends of oil were found, because they mainly affected by ships pollution. Although seasonal variation of Mercury(Hg), copper(Cu), lead(Pb) and cadmium(Cd) had no rules to follow, the concentration of mercury(Hg), lead(Pb) and copper(Cu) in haze days was higher than non-haze days. Particle sedimentation needs a period of time, they accumulate and grow when haze occurs, settle to the ocean when haze disappears. Heavy haze occurred frequently in winter, in which hour haze could last 12 hours. During this period, particulate matter load these metals, accumulate constantly, which settles in spring when haze disappears. So metals in sea water had a high concentration in spring. However, the above is just speculation, and why、how the metals settle to the sea water remains to be studied. Except active phosphate, active silicate and nitrate, other nutrients also had no rules to follow. Two kinds of possibilities were proposed: one is the nutrients carried by particulate matter are a secondary factor, the other is the sedimentation of particles lead to the changes of phytoplankton community, which alters nutrients’ distribution and concentration in the sea. The reason still needs to be studied.(3) Chlorophyll(a) is an important characterization of marine phytoplankton’s productivity. Chlorophyll(a) concentrations were not high generally when heavy haze appeared, while started to increase when haze converted to moderate or mild. In a haze circle, chlorophyll(a) concentrations increased during the haze, which decreased after the haze compared with their concentrations before the haze. And also, Chlorophyll(a) response to the haze with delayed effect. Light is a main factor to chlorophyll(a) in the early period of haze, then the main factor converts to nutrients. The density of phytoplankton and the biomass of zooplankton in haze days were higher than non-haze days in spring and summer. The density and biomass may have a similar response as chlorophyll(a): mild haze promotes their growth and reproduction, while heavy haze inhibits.(4) PM2.5 and temperature(T) showed a significant negative correlation. Fine particles such as sulfate aerosol can scatter and absorb solar radiation directly, the results of which is the reduction of sea surface temperature. Besides, the duration of haze and salinity had a significant positive correlation, while a negative correlation with temperature(T) and chemical oxygen demand(COD). PM2.5 and arsenic(As) showed a significant negative correlation, while a significant positive correlation with cadmium(Cr). The concentration of PM2.5 increased, which enhanced the solubility of Cd, so its concentration in the sea increased in haze days. The solubility of arsenic(As) reduced with the increasing of PM2.5, so the result showed the lower concentration in haze days. Haze duration and arsenic showed a significantly negative correlation, had no correlation with cadmium(Cd). We can explain this phenomenon as particle size gradually towards to the coarse mode, and the cadmium in the sea water dissolved to saturation when the concentration of PM2.5 remained a high value. PM2.5 and active silicate showed a significant negative correlation. Haze duration had a significant negative correlation with silicate, nitrate and phosphate. In the early period of haze, phytoplankton adopted silicate at first, then nitrate and active phosphate. From the correlation with PM2.5, it was inferred that these three nutrients came from the same source. Due to there were no silicate research in PM2.5 yet, these three nutrients may be from dust aerosol, which carried by air mass from the north.