# A Comparative Study of SOx, NOx, PM2.5 and PM10 in the UK and Poland from 1970 to 2020
## 4 Changes in Air Pollution in the UK Since the 1970s  
### Emissions of sulphur Oxides over the Years  
It can be seen from Figure 5 that the emissions of sulphur oxides have exhibited a steady decline since the 1970s, except for minor peaks in 1973 and 1979, attributed to harsh winters in those years [14], and a brief period in the late 1980s when emissions were relatively constant. This stability can be linked to heightened coal and energy usage for home heating during colder winter temperatures. Notably, this resulted in a sudden increase in sulphur dioxide (SO\({}_{2}\)) emissions, accompanied by elevated levels of nitrogen oxides (NO\({}_{x}\)) and particulate matter (PM2.5 and PM10). Furthermore, there is observable evidence indicating a slight reduction in total SO\({}_{2}\) emissions between 1997 and 1998. This reduction is attributable to the fact that the substantial decreases in emissions from the power generation sector were not as pronounced during the transition from 1997 to 1998 [8]. Sulphur dioxide emissions have experienced a remarkable 98% decrease since 1970, reaching 136,000 tonnes in 2020 (see Figure 6). The year 2020 saw a 13% reduction in emissions compared to 2019, marking the lowest level in the entire time series. This decline was attributed to a decrease in coal utilization in power stations, aligning with the ongoing trend of diminishing emissions from this particular source [15]. In addition, the implementation of more stringent limits on the sulphur content of liquid fuels contributed to the long-term reduction in emissions [12]. Figure 4: Air pollution in London. Data reproduced from [[https://ourworldindata.org](https://ourworldindata.org)]([https://ourworldindata.org](https://ourworldindata.org)) (accessed on 1 October 2023). The primary contributors to sulphur oxide emissions are solid fuels and petroleum products. Notably, the decline in emissions from petroleum use can be attributed to the reduced consumption of fuel oil and the lowering of sulphur content in diesel. An essential focus is on decreasing the sulphur content of gas oil, especially in sectors like domestic heating, commercial heating, and off-highway sources where gas oil is extensively employed. Power plants stand out as one of the largest sources of SO2 emissions [16]. It is worth noting that, in 1984, during a miners' strike, there was a substantial decrease in coal-based electricity production. Consequently, this led to a decline not only in SO2 emissions (Figure 6) but also in particulate matter, as depicted in Figure 5 for PM2.5 and PM10. Although historically UK has been reliant on coal, there has been a notable shift towards alternative fuels and power plants that produce fewer harmful substances over the past 50 years. Between 1970 and 1990, this shift resulted from a gradual increase in the utilization of nuclear power plants and improvements in efficiency. Subsequent to 1990, the decline accelerated due to a higher proportion of electricity generated in nuclear plants, alongside the adoption of Combined Cycle Gas Turbine (CCGT) stations and other  
Figure 5: Correlation between the mean air temperature and pollution level. gas-fired plants. CCGT plants, renowned for their efficiency, emit negligible amounts of SO2 compared to conventional coal- and oil-fired plants [17]. It is essential to highlight that industrial SO2 emissions stem from the combustion of coal and oil, certain refinery processes, and other chemical activities. The decline observed between 1970 and 1985 correlates with reductions in energy-intensive industries such as iron and steel, alongside a shift from coal and oil to natural gas. Despite the increase in road vehicles between 1970 and the early 1990s, emissions from road transport decreased as the sulphur content in diesel road vehicles declined. In the course of economic and industrial development, new emission standards were introduced, prompting the improvement or closure of outdated plants and incinerators.