Air quality in many cities has improved in line with changes in their economy and the regulation of emissions. Declining concentrations of air pollutants, most notably SO2, but later NOx can be ascribed to changes in industries and their control, and a more modern vehicle fleet (Brimblecombe, 2005; Power & Worsley, 2018). However, the link between emission control and reduced air pollutant concentrations is weakened because of a mediating atmospheric chemistry, best characterised by O3 formation. Its production is affected by hydrocarbons and nitrogen oxides. Ozone concentrations can increase when nitrogen oxide emissions decrease, so air pollution regulation needs to go beyond simple emission control and requires the application of air quality management (Elsom, 1992). Particulate matter is an important contributor to air pollution, yet significant fraction of the urban aerosol is again produced through reactions of primary pollutants in the atmosphere that lead to both inorganic components (Ravishankara, 1997), such as sulfates and nitrates. Secondary sulfate aerosol was probably more abundant in the past when SO2 levels were high. Secondary organic components best represented by the carboxylic acids, perhaps most notably low volatility dicarboxylic acids (Kawamura et al., 2001).
Taiwan (Fig. 1) experienced a rapid transformation from the largely agrarian colony left by the Japanese after World War 2, when it saw innovative expansion, such as that in the semiconductor industry. During the colonial period, Kaohsiung’s harbour became a focus for shipping and rail transport that allowed the city's development as a major hub for Taiwan’s south, with an industrial base in steel, cement, petrochemicals, paper making etc. The Taiwan Economic Miracle (Tsai, 1999), saw rapid growth of industrial infrastructure (~1960-1990), which contributed to pollutant emissions that paralleled the strengthening economy. Today, Kaohsiung remains an industrial city, though with an increasing shift in the local economy (Fig. 1c) towards financial services, tourism and the arts, with plans for the waterfront to become a landscape resource (KEC, 2021).
Post war industrialisation led to regulations needed to improve air quality, initially under the Air Pollution Control Act of 1975. The relaxation of Martial Law (late 1980s) saw newly democratised systems, and though electoral politics can stifle environmental debate, Taiwan established a cabinet-level Environmental Protection Administration (TEPA) in 1987. However, the 1975 Act was only effective after 1992, when stricter rules were implemented (Tang, 1993). Under democratisation this “credit for the improvement has been given to the air emission fee program that was first implemented” in 1995 (Tang and Tang, 2000). Before then, “the traditional command-and-control program and tax-allowance subsidy were the two major instruments used for air pollution control… ” (Shaw and Hung, 2001). Emission standards were established for power facilities 1994-05-04, while 1995-07-01 saw the introduction of an air pollution control fee for SOx emissions, and subsequent regulations to reduce volatile organic emissions (see supplementary table in Chen et al., 2014).
Postwar Kaohsiung expanded with an urban population of 168 008 in 1947 to 1 512 798 in 2017, where there were 2 776 912 in the municipal area. In parallel there was a growth of heavy industry (1976-86) and a mature stage for the heavy chemical industry (1986-96). Industrial zones were established in Fengshan (1974), Yongan and Linyuan (1974-75). Although the service industry has surpassed manufacturing in terms of value, steel, petrochemical, cement, shipbreaking, and processing exports remain substantial, though characterised by pollution. Challenge 2008: National Development Key Project encouraged investments in infrastructure such as High Speed Rail, Kaohsiung MRT, but with newer less polluting developments emerging from 2009: (i) biotechnology (ii) tourism (iii) green energy (iv) medical care (v) low intensity agriculture and (vi) cultural creativity (KCG, 2010).
The long history of industrial emissions has promoted many studies of air pollution in Kaohsiung, with deposit gauge measurements from the 1960s (Hsu and Wei, 1971; Selya, 1975; Wei, 1966), and more modern measurements from the 1970s (Chow et al., 1983). In Europe and North America there are estimates of long-term air pollutant loads in urban air using modelling (Brimblecombe, 1977), observations of smoke-days (Davidson, 1979) or pollutant deposit (Brimblecombe, 1982), but fewer from Asia (Ishikawa & Hara, 1997). Taiwan’s National Health Administration planned an optimal monitoring network for SO2 in Kaohsiung from 1975-1977 (Liang & Lee, 1980). There is a long series of studies of health (Yang et al., 1998), visibility (Lee et al., 2005; Lee, 2006) and PAHs (Lai et al., 2017). Early problems seem dominated by primary pollutants, but the situation with ozone has caused concern across recent years (Hung-Lung et al., 2007; Shiu at al., 2007; Tsai et al., 2012). Although there are also contemporary claims that for two decades, atmospheric visibility in Kaohsiung has worsened (Lee and Lai, 2018), they are not supported by Maurer at al. (2019), who suggest 2000-2015 saw improvement in Kaohsiung, paralleling change elsewhere in Taiwan, but not fully explained by lower RH or PM10.
Ammonia has not often been measured in Taiwan, but it may be important, given the density of pigs and poultry (Cheng et al., 2011). Additionally, Hsieh & Chen (2010) measured NH3 at industrial parks in southern Taiwan at Neipu, Pingtung and Pingnan over two consecutive days each (2003-09/2004-12), finding means of 90.4 ppb, 72.8 ppb and 84.9 ppb; while at the National Pingtung University of Science and Technology campus dormitory and a bamboo grove near the village of Laopi in Pingtung County concentrations were 52.2 ppb and 4.6 ppb showing the significance in the region. Vehicles represent a potential source of NH3 in urban areas, e.g., in urban Guangzhou vehicles produce 19% of the ammonia (Liu et al., 2014), although 2006 estimates across the Pearl River Delta suggest vehicles accounted for just 2.5% (Zheng et al., 2012).
This paper explores a fifty-year history of air pollution in Kaohsiung to understand the changes and assess the relevance of shifts in the economy and regulatory activity. The city represents an interesting and somewhat isolated location, where there have been great changes as it moved from an unregulated industrial centre for manufacturing, steel-making, oil refining and shipbuilding to a place aspiring to be noted for international exhibitions, tourism and the arts. This transition has required more stringent urban planning and concerns over air quality and visibility. Although coastal cities have been well studied, the difficulty of maintaining sites may limit measurement duration (e.g. Alastuey et al., 2004; Galindo et al., 2020), but the longer record used here means we can explore how urban transformation is reflected through a half century of development. We give special attention to changes in the threat to health, agricultural production and visibility.