An Approach for Quantifying a Regional Haze Stress: Case Study in Three Cities of Taiwan

Abstract

This study proposes an approach of evaluating the haze stress index (HSI) and quantifying people’s feelings for haze stress. The three special municipalities in Taiwan were selected as representative cities of slightly, moderately, and heavily contaminated with fine particulate matter (PM2.5) to evaluate the adaptability of the proposed approach. Equations with weightings of parameters to evaluate four temporal HSIs—hourly, daily, monthly, and yearly HSIs—were established. The parameters were measured PM2.5, relative humidity, and secondary organic aerosol (represented by the sum of measured O3 and NO2). The results of evaluating the HSIs in the three cities demonstrated that the inverse-variance weighting method is the best because the haze stress sensitivities in the four temporal periods were higher than those obtained using the unit and variance weighting methods to respond to the real situation of air quality. Variation in the four temporal HSIs for the three cities demonstrates that the variation increases with an increasing level of air pollution. When comparing between 2015 and 2018, the fractional reductions in HSIs in the slightly, moderately, and heavily contaminated cities were ≤18.4%, ≤10.8%, and ≤11.3%, respectively. It is recommended that the HSIs are categorized into five haze stress groups based on the haze stress level. The people’s feelings in the three cities on the haze stresses were represented using the established quantifying descriptors in detail. The results show that the proposed approach can provide quantification indices of haze stress and people’s feelings in a regional haze, thereby firmly establishing the governmental improvement policy.