Seasonal Characteristics and Particle-size Distributions of Particulate Air Pollutants in Urumqi

Urban particulate air pollution is a known cause of adverse human health effects worldwide. Urumqi is a large oasis city in which rapid urbanization has caused a series of eco-environmental problems including serious air pollution, water shortage, dense population, excess energy consumption, and the creation of an urban heat island, among others. Coal is the most important source of energy and air pollutants that are poorly dispersed into the natural surroundings are the main reasons for serious pollution in the Urumqi urban area. Using differential optical absorption spectroscopy (DOAS), aerosol levels were determined using the double optical path method. We found that aerosol concentrations in Urumqi increased rapidly in winter, and that the concentration of fine particles was much higher than that of coarse particles. The background aerosol concentration was highest in winter in the research area, and the air-flow speed had a significant impact on this because high speed surface winds that correspond to high air flows can transport the aerosol to other places. Some of the observed day-to-night differences may be caused by differing wind directions that transport air masses from different emission sources during the day and the night. Daily and seasonal differences in PM_1.0 concentrations of different grades of polluted air were statistically analyzed using average daily concentration data for particles smaller than 10, 2.5 and 1.0 microns (PM₁₀, PM_2.5 and PM_1.0), and meteorological observations for Urumqi, Tianshan District in 2010.

Environmental impacts of tropospheric volcanic gas plumes

Recent studies suggest that the environmental effects of volcanic gas emissions in the lower troposphere have been underestimated. This chapter first briefly summarizes the techniques available for characterizing tropospheric volcanic gas plumes, including the composition and fluxes of emitted gases and aerosols, as well as their atmospheric dispersion. The second part documents the contribution of gas emissions from degassing craters to the composition of the atmosphere, including effects from dry and wet deposition chemistry. The third section deals with the detrimental impacts on vegetation, soils, and groundwater in relation to passive degassing activity. Improved understanding of the impacts of volcanic degassing on the atmospheric and terrestrial environment will require: (1) systematic two-dimensional and three-dimensional measurements of tropospheric volcanic plumes, (2) development of general physical and chemical models to describe the fate of volcanic gases and aerosols during transport in the troposphere, and (3) investigation of the response of diverse ecosystems to volcanogenic air pollution.

Repetitive genetic inversion of optical extinction data

We describe a genetic method of deriving aerosol size distributions from multiwavelength extinction measurements. The genetic inversion searches for log-normal size distribution parameters whose calculated extinctions best fit the data. By repetitively applying the genetic inversion using different random number seeds, we are able to generate multiple solutions that fit the data equally well. When these solutions are similar, they lend confidence to an interpretation, whereas when they vary widely, they demonstrate nonuniqueness. In this way we show that, even in the case of a single log-normal distribution, many different distributions can fit the same set of extinction data unless the misfit is reduced below typical measurement error levels. In the case of a bimodal distribution, we find many dissimilar size distributions that fit the data to within 1% at six wavelengths. To recover the original bimodal distribution satisfactorily, we found that extinctions at ten wavelengths must be fitted to within 0.5%. Our results imply that many size distributions recovered from existing extinction measurements can be highly nonunique and should be treated with caution.