Ozone is not usually generated directly from a pollutant source like other air pollutants such as carbon monoxide, respirable particulates and formaldehyde. Instead, it is a byproduct of a complex photochemical reactions (with the presence of sunlight) involving volatile organic compounds (VOCs) and nitrogen oxides as a secondary pollutant. Being a photochemical oxidant and the main component of smog, ozone can cause detrimental health effects to humans when inhaled and damage plants due to its phytotoxic characteristic.
This study was conducted in urban, suburban and rural areas of Peninsular Malaysia to compare the concentrations of ground-level ozone, VOCs and nitrogen oxides in order to determine the concentrations and causes of ground-level ozone in these 3 areas respectively. From the data collected from year 2005 to 2009 at the 3 areas, the average daily and average daily maximum ozone concentrations were presented in the chart below. Overall, suburban area had the highest concentration of ground-level ozone, followed by the urban area and rural area. Air pollutants consisted of nitrogen oxides was blown downwind to suburban area, causing a raise of ozone concentration there. Even though urban area is the source of nitrogen oxides, high level of nitrogen oxides can reduce the concentration of ozone through a chemical process called titration in which nitrogen oxide is converted into nitrogen dioxide through reaction with ozone. This phenomenon of higher ozone concentration in suburban area compared to urban area had been recorded in several other studies.
The maximum concentration of ground-level ozone allowed according to Malaysian Department of Environment is 100 ppbv (part per billion volume). Even though the average daily and average daily maximum ozone concentrations did not exceed 100 ppbv, the number of days when the ground-level ozone concentrations exceeded the limit was 5 to 24 days per year and 2 to 12 days per year for suburban area and urban area respectively. Throughout the study period of 5 years, concentrations of ground-level ozone in rural area had not exceeded the limit. The total number of days when concentrations of ozone exceeded 100 ppbv each year for urban, suburban and rural areas is portrayed in the following chart.
This study shows that suburban area had a higher concentration of ground-level ozone compared to urban and rural area, affected by the amount of nitrogen oxides present. Other factors which control the generation of ground level ozone are solar radiation intensity and wind pattern, which are not included in this article. As a conclusion, the findings of this study suggest that reducing the traffic volume in urban area will cut down the amount of ground-level ozone in downwind areas. More studies regarding the influence of stratospheric ozone (the one that protects the earth from harmful radiation) and specific VOC molecules should be investigated to look into other sources of ground-level ozone.
Source: Banan, N., Latif, M. T., Juneng, L. & Ahamad, F. (2013). Characteristics of surface ozone concentrations at stations with different backgrounds in the Malaysian Peninsula. Aerosol and Air Quality Research, 13: 1090 – 1106
Disclaimer: Copyright belongs to the original authors of the paper, Enviroverks does not own any of the content. The purpose of this article is to present the information from a scientific paper in a way general public can understand. Charts were added for illustration purpose without altering the data.