Ozone-related premature mortality highest in India

Health Care Comments Off

Air pollution has been under spotlight for quite some time now. Air quality in Delhi, in particular, has often been in the ‘poor’ or ‘very poor’ category since Diwali last year. Environmental pollution adds to the global burden of disease, both morbidity and mortality. High air pollution levels have been implicated in many diseases including respiratory disease, diabetes and heart disease.

Air Quality Index (AQI) takes into account eight air pollutants: PM10, PM2.5, nitrogen dioxide (NO2), sulphur dioxide (SO2), Ozone (O3), Lead (Pb), Ammonia (NH3), carbon monoxide (CO). There are six AQI categories: Good (0-50), Satisfactory (51-100), Moderately polluted (101–200), Poor (201–300), Very Poor (301–400) and Severe (401-500).

A new report ‘State of Global Air 2017’ released by the Health Effects Institute (HEI) and Institute for Health Metrics and Evaluation (IHME) last week states that 92% of the world’s population lives in areas with unhealthy air. All told, long-term exposure to fine particulate matter– the most significant element of air pollution– contributed to 4.2 million premature deaths and to a loss of 103 million healthy years of life in 2015, making air pollution the 5th highest cause of death among all health risks, including smoking, diet, and high blood pressure. As per the report, India along with China accounted for more than half of the total global attributable deaths. This report also highlighted ozone-related mortality. Globally there was a 60% increase in ozone-attributable deaths, with a striking 67% of this increase occurring in India. An estimated 2.54 lakh deaths were attributable to exposure to ozone and its impact on chronic lung disease. India recorded the highest number of premature deaths due to ozone pollution (107,800), its toll 13 times higher than Bangladesh (7900) and 21 times higher than Pakistan (5000).

This report quantified air pollution using two main pollutants: PM2.5 and ozone. Surface or ground ozone is harmful, unlike the ozone layer high up in the atmosphere, which acts as a shield and protects from harmful UV rays. Ground ozone is formed by the reaction of pollutants in the vehicular and industrial emissions with sunlight. Nitrogen oxides (NOx) and volatile organic compounds (VOC) are the ozone precursors. Traffic emissions constitute more than 50% of the ozone precursors.

While this report defined ozone-related deaths in numbers, it did not clarify as to how these deaths were confirmed to be due to ozone. Also, paradoxically, the levels of ozone are higher in rural areas compared to urban areas. This is because the levels of NOx are lower in rural areas. Cities have a higher NOx levels due to traffic, which neutralize ozone and keep it in or near permissible limits. Levels of PM2.5 are higher in cities. Ozone is associated with respiratory disease independent of exposure to PM2.5.