Fifty-year change in air pollution in Kaohsiung, Taiwan.

The change in air quality in cities can be the product of regulation and emissions. Regulations require enforcement of emission reduction, but it is often shifting economic and societal structures that influence pollutant emissions. This study examines the long-term record of air pollutants in Kaohsiung, where post-war industrialisation increased pollution substantially, although improvements are observed in recent decades as the city moved to a more mixed economy. The study tracks both gases and particles across a period of significant change in pollution sources in the city. Concentrations of SO and aerosol SO were especially high ~1970, but these gradually declined, although SO to a lesser extent than its precursor, SO. While twenty-first century emissions of SO and NO have declined, this has been less so for NH, because it arises from predominantly agricultural sources. The atmosphere in Kaohsiung continues to have high concentrations of O, and these have risen in the city, likely a product of less titration by NO. The changes have meant that ozone has become an increasing threat to health and agriculture. Despite a potential for producing (NH)SO and NHNO aerosols, a product of a relatively constant supply of NH, visibility has improved in recent years. Emissions of SO and NO should continue to be reduced, as these strongly affect the amount of fine secondary aerosol. However, the key problem may be ozone, which is difficult to control as it requires careful consideration of the balance of NO and hydrocarbons so important to its production.