Temperature and air pollution relationship during heatwaves in Birmingham, UK

Highlights

• Assessing the relationship between temperature and air pollution during heatwaves.

• Birmingham was selected as study location.

• Results reveal a positive linear relationship between temperature and air pollution during heatwaves.

Abstract

While temperature has long been known as a catalyst for pollutants to be more airborne, it is unclear how an increase in temperature affects air pollution during heatwaves. Through a regression analysis of the relationship between ozone (O₃), particulate matter (PM₁₀, particles less than 10 μm in diameter), nitrogen dioxide (NO₂), and temperatures in urban and rural areas of Birmingham, it was found that during heatwaves, all pollutant levels rose at each site, with the maximum temperature coinciding with the peak levels of O₃ and PM₁₀. These findings established that the influence of temperature on air pollution did not change according to rural or urban locations although air pollutants (O₃, PM₁₀, and NO₂) increased with increasing temperatures, particularly during heatwaves. Levels of ozone were found to increase by more than 50% with increases in temperature. This supports studies where the incidence of high levels of pollutants has conclusively been found to be much more prevalent during prolonged heatwaves. The implications of these findings are important to the establishment of long-term prevention measures in heatwave plans. When a heatwave is forecast, additional measures to reduce air pollutant concentrations may be appropriate when commencing emergency responses.

Introduction

Worsening air quality and extreme weather events, such as heatwaves, are increasingly affecting people worldwide. Heatwaves have long been known as an important driver of air pollutant levels, resulting in various health, environmental, and economic impacts (Cheval, Dumitrescu, & Bell, 2009; García-Herrera, Díaz, Trigo, Luterbacher, & Fischer, 2010). Air pollutants whose concentrations and impacts are known to be affected by heatwaves include ozone (O₃), particulate matter (PM) and nitrogen dioxide (NO₂). These pollutants, when emitted into the atmosphere from a variety of natural and anthropogenic sources, are a major threat to human health (World Health Organization, 2010). The concentration of these pollutants in ambient air depends on the level of emission and the ability of the atmosphere to absorb or disperse these pollutants (World Health Organization, 2010).

Since meteorological variables such as temperature and concentrations of air pollutants vary on a daily basis, it is important to consider their relationship in the planetary boundary layer, since the atmosphere is the medium in which air pollutants are transported away from the source. Lee et al. (2006) indicated that during photochemical pollution episodes, air pollutants (O_3, PM_10, and NO₂) are the result of a mixture of various meteorological effects and chemical reactions. These pollutants are of the greatest health concern, as their emissions may be exacerbated during heatwaves (Analitis et al., 2014; Fouillet et al., 2006; Johnson et al., 2004). As a result, sensitive individuals may not only be stressed by high temperatures, but may be more subject to mortality due to air pollution during heatwaves (Analitis et al., 2014). Unusually hot weather during summer led to elevated levels of air pollutants during the heatwaves that occurred in Athens, Greece, between June and July 2007 (Fischer, Brunekreef, & Lebret, 2004). Theoharatos et al. (2010) found a significant correlation between heatwaves and average hourly concentrations of O₃, NO₂ and SO₂ in Athens. Similarly, the combination of elevated air pollution levels and high temperatures was implicated in the increase in urban heat islands (UHIs) and air pollution in London, England (McMichael et al., 2003; Rooney, McMichael, Kovats, & Coleman, 1998).

Heatwaves are particularly intense in urban areas, where surface characteristics alter the temperature differences between urban and rural areas. The differences are generated by low levels of vegetation in cities, and the production of anthropogenic heat and air flow caused by urban infrastructure such as buildings and asphalt streets (Bibri & Krogstie, 2017). Mirzaei (2015) indicated that extreme air temperatures in cities (UHIs) increase heat- and air pollution-related mortality and raise the energy demands for cooling buildings, which in turn leads to a further increase in air pollutants and greenhouse gas emissions. Despite this, several studies have shown that sustainable urban planning, and smart city design including green roofs and cool pavements could significantly reduce both UHIs and air pollution; especially O₃, NO₂, and PM₁₀ (Bibri & Krogstie, 2017; McDonald et al., 2007; Silva, Khan, & Han, 2018; Yang, Yu, & Gong, 2008).

Previous studies investigating temperature and air pollution during heatwaves (Fischer et al., 2004; Fouillet et al., 2006) have only explored the role of air pollution in modifying the effects of heatwaves on mortality. There is a dearth of research studies examining the relationship between temperature and air pollution during heatwaves, without considering mortality. In addition, there seems to be no research into the spatial relationships of temperature and air quality during heatwaves, such as between urban and rural areas in England. The objectives of this study are to: (1) assess the relationship between temperature and air pollution during heatwaves; (2) quantify the impact of temperature on air pollutants (specifically ozone (O₃), particulate matter (PM₁₀) and nitrogen dioxide (NO₂)); and (3) investigate the difference in that impact between urban and rural areas of Birmingham in the United Kingdom during heatwave events identified between 2003 and 2013.