The Relationship between Ozone and Temperature in Greater Kuala Lumpur, Malaysia

A positive relationship between temperature (T) and the pollutant ozone (O₃) has been widely reported. Increases in T linked to anthropogenic climate change could promote increases in O₃, but the importance of this “ozone-climate penalty” has received little attention in tropical regions. Here we add to available evidence from the tropics by analysing the O₃-T relationship in Greater Kuala Lumpur (GKL), Malaysia. We focussed on observations from three Malaysian Department of Environment air quality monitoring sites, covering the 10-year period 2007−2016. We identified consistent patterns across the sites, with high T and O₃ year-round, modest seasonality, and a year-round positive O₃-T relationship. We quantified this relationship using regression slopes, which varied across the three sites between 2.8−4.0 ppb °C⁻¹ for 50^th percentile O₃ and between 5.6−6.7 ppb °C⁻¹ for 95^th percentile O₃. Over the study period, we found that O₃ in fixed T bins, and O₃-T slopes, were tending to decline, but that counteracting increases in T appear to result in little change in overall O₃ levels. This is an indication of an “ozone-climate penalty” in GKL. We also characterised increases in O₃ during a period of exceptionally high T in 2016. Our findings of a strong positive O₃-T relationship, of indications of a declining sensitivity of O₃ to T, and of co-occurring extremes of O₃ and T are broadly consistent with literature covering cities in other regions, though these features are relevant year-round in GKL. Further work is required to understand the influences of chemistry, emissions and other meteorological conditions associated with high T on O₃ and the O₃-T relationship in this region. Such an understanding would inform further controls on emissions of O₃-precursors in GKL, which appear to be critical to achieving improvements in future O₃ air quality under ongoing warming.