Visibility Variation with Air Qualities in the Metropolitan Area in Southern Taiwan

Principal component analysis (PCA) was used to analyze variationsin visibility compared with (1) variations in meteorological variables in the period 1961 to 1998, and (2) criteria air pollutant (SO2, CO, O3, NOx and PM10) concentrations monitored between 1994 and 1998, in the Kaohsiungmetropolitan area. Whilst average visibility during the 1960'sexceeded 20km, it had deteriorated to 5–10 km in theperiod 1994 to 1998. PCA identified seven components witheigenvalues greater than one. The principal componentsidentified accounted for variability related to PM10concentration, ozone-related pollutants, oil combustion,and traffic emissions. Furthermore, spatial and temporalvariations in PM10 were consistent throughout thecity. Variation in SO2 levels followed a similarpattern at Tsoying, Shanming, Chiankin and Chiancheng.Industrial pollution and traffic emissions, SO2, COand NOx, from the Hsiaokang area remained within thearea. However, similar patterns of SO2 andNOxat Fengshan and Jenwu indicate that industrial emissionsfrom the latter were probably transported to the former.Much of the first principal component is based onPM10 variability, suggesting that, of the fivecriteria pollutants studied, PM10 is the majorcontributor to visibility deterioration. It is known thatPM2.5 concentration is more closely associated withvisibility changes than is PM10. However, becausePM10 and PM2.5 are strongly associated inKaohsiung, a targeting reduction in PM10 may imply areduction in visibility.