Zhou Xiuji

Characteristics of the spatial distribution and yearly variation of aerosol optical depth over China in last 30 years

The yearly and monthly mean aerosol optical depth (AOD) at 0.75 μm were retrieved using a new method improved from Qius algorithm from the data of daily direct solar radiation, sunshine duration, surface pressure, and vapor pressure at 46 A class solar radiation stations over China from 1961 to 1990, as well as the Total Ozone Mapping Spectrometer (TOMS) derived ozone data from 1979 to 1990. Then the analysis on the distribution of yearly mean AOD and its variation over China in the last 30 years were made from the derived AOD data. It was found that the yearly mean AOD has pattern related to the geographical features with the maximums over basins. One of the maximum centers at Sichuan Basin, southwest of China, and the other is in the south Xinjiang Basin, northwest of China. In most areas of China the maximum of AOD occurs in spring, but the season of reaching the minimum varies with regions. The monthly mean AOD distributions are similar to the annual mean pattern, having strong ”basin“ effect, but the month-to-month differences are still obvious. In addition, AOD increased dramatically over China mainland from 1961 to 1990, particularly in the middle and lower reaches area of the Yangzi River and the east part of southwest China. In north China, Shandong peninsula, the east part of Qinghai Province, and coastal areas of Guangdong Province, a significant increasing trend of AOD is shown, while in most parts of northwest China and northeast China, the increase trend is less significant. However, in the western part of Xinjiang autonomous region and part of Yunnan Province, only a decreasing tendency is shown. Of the total 46 stations, the yearly averaged AOD variation curve can be briefly divided into two periods. One period is from 1961 to 1975, when AOD is smaller than the 30 year mean value; the other period is from 1976 to 1990, when AOD is higher than the mean value. Except for the peak in 1982 and 1983, which may be attributed to the eruptions of El Chichon, the curve shows a significant increasing trend from 1961 to 1990. The monthly averaged AODs of the total 46 stations also obviously increased.

Is ozone pollution affecting crop yields in China

Newly available data from non-urban locations in China along with regional model simulations suggest that ground-level ozone may be sufficiently high to affect Chinas winter wheat production. As non-urban ozone increases with industrialization, its effects on crops could hinder efforts to meet increasing food demands in the coming decades, in China.

A nonurban ozone air pollution episode over eastern China: Observations and model simulations

Air quality data gathered from five nonurban sites in China over a 12-month period from August 1994 to August 1995, along with meteorological observations from the same region and period, are used to identify and characterize a nonurban ozone (O3) pollution episode in China. Because of the influence of the Asian Monsoonal Circulation, high O3 concentrations were not observed at the nonurban sites during the summer months. However, enhanced O3 concentrations were observed during the other seasons, especially the fall and early winter. A more detailed inspection of the O3 data during the period from October 15, 1994, to January 15, 1995, indicated the occurrence of a multipleday episode in late October/early November when high O3 concentrations were observed at all four monitoring sites located in eastern China. Meteorological conditions during the episode were characterized by the presence of a strong and stationary high-pressure ridge over eastern China; synoptic conditions quite similar to those observed during regional O3 pollution episodes over the United States, Canada, and Europe. An updated version of the Regional Acid Deposition Model (RADM) driven by meteorological fields derived from the Regional Climate Model (RegCM) and spatially disaggregated anthropogenic emissions prepared by the Chinese Academy of Meteorological Sciences is used to simulate 3 months of the observed O3 data from China. Comparisons between observations and model calculations indicate that the model is able to reproduce some of the key features of the O3 distribution and its relationship to the concentration of one primary pollutant (i.e., sulfur dioxide) provided the comparison is made using averaging times of several days or more. However, simulation of day-to-day variations in O3 at a given site was poorly correlated with observations. Model simulations suggest that peak O3 concentrations during this episode would respond to changes in NOx and VOC emissions in a spatially inhomogeneous manner. In general, rural areas in southern China tend to be NOx-limited, but rural areas in northern China tend to be VOC-limited. The Yangtze Delta region, where the highest O3 concentrations were observed and predicted to occur, was found to be transitional between VOC and NOx limitation.

Characteristics of the heat island effect in Shanghai and its possible mechanism

The characteristics of the urban heat island effect and the climate change in Shanghai and its possible mechanism are analyzed based on monthly meteorological data from 1961 to 1997 at 16 stations in Shanghai and its adjacent areas. The results indicate that Shanghai City has the characteristics of a heat island of air temperature and maximum and minimum air temperature, a cold island of surface soil temperature, a weak rainy island of precipitation, and a turbid island of minimum visibility and aerosols, with centers at or near Longhua station (the urban station of Shanghai). Besides theses, the characteristics of a cloudy island and sunshine duration island are also obvious, but their centers are located in the southern part of the urban area and in the southern suburbs. A linear trend analysis suggests that all of the above urban effects intensified from 1961 to 1997. So far as the heat island effect is concerned, the heat island index (difference of annual temperature between Longhua and Songjiang stations) strengthens (weakens) as the economic development increases (decreases). The authors suggest that the heating increase caused by increasing energy consumption due to economic development is a main factor in controlling the climate change of Shanghai besides natural factors. On the other hand, increasing pollution aerosols contribute to the enhancement of the turbid island and cooling. On the whole, the heating effect caused by increasing energy consumption is stronger than the cooling effect caused by the turbid island and pollution aerosols.

A nonlinear regional prediction experiment on a short‐range climatic process of the atmospheric ozone

A regional prediction experiment on the distribution of the atmospheric ozone column over China is performed by means of a spatiotemporal artificial neural network system (STANNS) built by using the monthly mean values of Total Ozone Mapping Spectrometer (TOMS) data from the Nimbus 7 satellite. The experiment region is situated from 72.5°E to 128.75°E and from 22°N to 49°N and divided into a rectangular grid net of 16×10. The data used cover 174 months from November 1978 to April 1993; those from the first 150 months were used to construct STANNS, and those from the last 24 months were used to test the prediction ability. The experiment results are encouraging. All the values of the correlation coefficient between the prediction and the actual fields for 24 or more samples exceed 90% at the lead time of not more than 6 months. This shows that there exists a good agreement between the prediction and the actual fields. In addition, some important features in the ozone distribution, such as the unusual depletion area over the Tibetan Plateau in summer, are also predicted very well. The results also show that, in a rough sense, the prediction accuracy decreases with the increasing of lead time.

The possible influences of the increasing anthropogenic emissions in India on tropospheric ozone and OH

A 3-D chemical transport model (OSLO CTM2) is used to investigate the influences of the increasing anthropogenic emission in India. The model is capable of reproducing the observational results of the INDOEX experiment and the measurements in summer over India well. The model results show that when NOx and CO emissions in India are doubled, ozone concentration increases, and global average OH decreases a little. Under the effects of the Indian summer monsoon, NOx and CO in India are efficiently transported into the middle and upper troposphere by the upward current and the convective activities so that the NOx, CO, and ozone in the middle and upper troposphere significantly increase with the increasing NOx and CO emissions. These increases extensively influence a part of Asia, Africa, and Europe, and persist from June to September.

Impact of Aircraft NOx Emission on NOx and Ozone over China

A three-dimensional global chemistry transport model (OSLO CTM2) is used to investigate the impact of subsonic aircraft NOx emission on NOx and ozone over China in terms of a year 2000 scenario of subsonic aircraft NOx emission. The results show that subsonic aircraft NOx emission significantly affects northern China, which makes NOx at 250 hPa increase by about 50 pptv with the highest percentage of 60% in January, and leading to an ozone increase of 8 ppbv with 5% relative change in April. The NOx increase is mainly attributed to the transport process, but ozone increase is produced by the chemical process. The NOx increases by less than 10 pptv by virtue of subsonic aircraft NOx emission over China, and ozone changes less than 0.4 ppbv. When subsonic aircraft NOx emission over China is doubled, its influence is still relatively small.