Abstract
Ground level ozone concentration is dependent on its precursors, such as Nitrogen Oxides (NOx) and hydrocarbons (HCs) and meteorological parameters, most importantly air temperature. Positive ozone-temperature slope at average temperature is well-documented. However, how this relationship breaks at extremely high temperature in hotter climates is still debatable. As this could have implications for long term global modelling predictions, this paper explores evidence for a negative ozone-temperature slope during atypically high temperature events in Makkah, Saudi Arabia, where temperature levels as high as 50°C are recorded. At temperature levels (15–42°C) statistical analysis showed positive ozone-temperature slopes, however the slopes became negative at atypically high temperature levels (> 42°C). Using data when hourly mean temperature was greater than 42°C, Quantile Regression Model (QRM) showed negative ozone-temperature slopes. The negative slopes at quantile 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9 were –1.88, –5.83, –7.89, –7.08, –11.11, –15.00, –18.28, and –28.57 µg/m3/°C, respectively. Mean slope determined by linear regression was –11.51 µg/m3/°C. Furthermore, the negative slopes were stronger at higher quantiles of ozone distribution, indicating non-linearities in the association of ozone and temperature. Reduction in the levels of ozone precursors, such as total hydrocarbons (THCs) and nitrogen dioxide (NO2) is probably the most likely reason for the negative ozone-temperature slope at extremely high temperature. Previously concerns have been expressed that under the warming climate scenario increasing temperature may further increase ozone levels, particularly in urban areas during pollution episodes, however this study suggests the opposite at extremely high temperature in hot arid climatic conditions.
Highlights
Ozone (O3) is a secondary air pollutant and is formed by photochemical oxidation of Volatile Organic Compounds (VOCs) and Nitrogen Oxides (NOx) in the presence of solar radiation (AQEG, 2009)
(Leeth, Sharaai, and Azizia) in Makkah averaged over ten years (2003–2012) are depicted in Fig. 2, where it can be observed that observed temperature is slightly different at various monitoring stations, they follow the same annual cycles
In Saudi Arabia the other seven months are designated as winter months, the average monthly temperature in most of these months is higher than 25°C, which might not be considered as winter months in some other colder countries like United Kingdom
Summary
Ozone (O3) is a secondary air pollutant and is formed by photochemical oxidation of Volatile Organic Compounds (VOCs) and Nitrogen Oxides (NOx) in the presence of solar radiation (AQEG, 2009). Ozone is a reactive oxidant and is actively involved in many chemical reactions, including biochemical reactions. It plays a vital role in atmospheric chemistry and contributes to the greenhouse effect (IPCC, 2001). At higher concentrations ground level ozone has been linked with various health problems, damage to agricultural crops and other materials (e.g., Bell and Treshow, 2008). Ozone adversely affects human health due to its irritant properties and induction of an inflammatory response in the lungs, causing health problems and premature deaths (AQEG, 2009). Analysing the health impacts of ozone World Health Organisation (WHO, 2008) has reported that high levels of ground level ozone causes about 21000 premature deaths and 14000 respiratory hospital admissions annually in 25 European Union countries. High ozone concentrations are usually observed during periods with sustained high temperatures and sunshine because such conditions favour photochemical ozone formation
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