Linear decomposition-based methodology for determining the relative importance of wind and non-wind phenomena on observed air quality.

摘要

Air pollution in Hong Kong (HK) is becoming more significant. Many people have expressed their concern about changes in air quality. The problems and concerns have been manifest, in recent years, in HK and the Pearl River Delta (PRD) region. Typically, it is believed that increased emissions should be blamed for causing air pollution in this region. However, the authorities explain that increased occurrence in calm/light wind conditions is also important in hindering dispersion of air pollutants. Understanding the real causes can benefit in setting the best control policies.;The conflict between the "emission" and "wind pattern" viewpoints can be resolved if we can distinguish the respective contributions of wind changes (wind influence) and emission strengths (non-wind influence) on air quality. However, up to now, there has been no systematic way to determine the relative importance of these two main phenomena on air quality. Most current related research can only show they have an impact on air quality. Little has compared them quantitatively.;This research first investigated whether the frequency of calm/light wind conditions is closely related to the concentration of pollutants. The plotted charts show high wind speed with low pollutant concentration and vice versa. Although the frequency distributions of wind speed in 2000 -- 2003 versus 2004 -- 2007 do show that there was a higher frequency of low wind speeds in the latter period, when pollution levels are compared during periods of similar wind speed, they are higher in the latter period than in the former. A linear decomposition-based methodology is proposed to distinguish the relative importance of these two main phenomena on air quality. Based on the hourly wind data (speed and direction) and pollutant concentration, the wind frequency and pollutant emission "roses" (circular frequency diagrams) are established. Hypothetical pollutant concentration can be calculated from these two roses. By comparing the hypothetical pollutant concentration with the actual measurement, the relative importance of these two main phenomena on average pollutant concentration in two periods can be determined respectively quantitatively.;Last, the respirable suspended particulates (RSP), ozone (O3), nitrogen dioxide (NO2) and sulphur dioxide (SO2) in 2000 -- 2007 in HK were analyzed and two past air quality related controversial cases were also studied.;It is shown that the non-wind influence on observed air quality in HK was more significant than the wind influence in annual-based comparison.