Measuring and modeling acid deposition in China
Acid deposition has become an important topic of research in China over the past several years. As a result of China's extensive fossil fuel burning, sulfur dioxide (SO2) and other pollutants are emitted into the atmosphere, and many cities have levels of these pollutants that exceed standard levels. This is especially true in cities in northern China which use a good deal of space heating in homes and other buildings. In the southern part of China, acid precipitation is becoming a significant issue. As a result, China's meteorological administration has set up a series of 100 monitoring stations, including 30 permanent ones, to monitor pH values, and various pollutants in order to better understand acid rain trends. These stations have been collecting measurements for two years and data is now available.
This measurement data is being used to simulate acid deposition in a regional acid deposition model (RADM). The RADM is a meso-scale meteorological model which uses emissions data on NOx, SOx and aerosols as input parameters to simulate acid deposition in China. After using the model to simulate acid deposition, this output is compared with measurements of acid deposition from the monitoring network with good results. So far, only wet deposition has been measured but it is hoped that dry deposition can soon be added to the measurement program.
Measuring and modeling ozone in China
Ozone in both the stratosphere and troposphere is an important species for study. The concern over ozone stems from the fact that the "good ozone" in the stratosphere which protects the biosphere from harmful ultraviolet radiation from the sun is decreasing, while "bad ozone" in the troposphere, which is a pollutant that is harmful to ecosystems, is increasing in recent decades.
Ozone is produced in a photochemical reaction by NOx, hydrocarbons and other precursors in the presence of sunlight. Recent research suggests that China has a significant ozone problem. Ozone concentrations are now measured at five monitoring stations. In rural areas, annual average concentrations are 40-50 ppbv, while urban annual averages are around 60 ppbv. Summertime short-term average levels are much higher, reaching 200 to 300 ppbv and the frequency of exceeding standard levels increases each year due to increases in emissions of NOx, SOx, aerosols, and hydrocarbons from burning fossil fuels. Concern over this situation prompted the formation of the China Ozone Research Program (CORP).
Some interesting results have already come out of this program, including the fact that there is strong diurnal variation in ozone measured at stations in Linan and Waliguan (Figure 13.1). Data also reveal a very different ozone pattern between east and west in China. Extremely low summertime ozone levels over the Tibetan plateau have also been discovered by the CORP. Though the reasons for these ozone variations are not yet understood, additional research is underway to explain these phenomena and also to explain fundamental chemical and meteorological processes with these data.
When data from the Total Ozone Mapping Spectrometer (TOMS) were compared with that of the CORP stations, the results were encouraging. There was less than a 6% difference between them.
As part of the search for new and improved scientific models to explain the ozone data, a box model based strictly on chemical reactions (no chemical transport is included) has been developed. In this model, all the parameters come from the measurement data: temperature, relative humidity, ozone concentrations, etc. The ozone loss and ozone production rates are simulated and net ozone production is determined. The model is as yet unable to reproduce net negative results like those observed at Waliguan Mountain, but can produce high concentrations of ozone such as those observed at Linan. The researchers have also developed a regional ozone model for simulating tropospheric ozone.
Some of the scientific research issues that need to be addressed in the future include:
The fact that high ozone concentrations are quite episodic makes experiments to measure ozone damage on crops very difficult.