Subscribe
Rising temperatures induced by climate change lead to higher tropospheric ozone (O3) levels, particularly in cities. Tropospheric O3 adversely affects respiratory health in humans. Human exposure to O3 has increased globally at a rate of 0.25 ppb (parts per billion) between 2000 and 2019, according to the latest Global Environment Outlook (GEO-7) report by the United Nations.
O3 exposure contributed to half a million premature deaths worldwide and mortality due to it increased by 46 per cent between 2000 and 2019, according to the analysis.
During the same time period, population-weighted O3 concentrations increased by more than 24 per cent in cities across South America, Africa, Western Europe, and South and Southeast Asia.
Rising temperatures affect air pollution trends by contributing to more frequent and intense wildfires and related smoke events and longer pollen seasons.
Global atmospheric methane concentrations have increased over the past decades and currently contribute about 35 per cent of the O3 burden globally. While O3 peaks have declined, baseline O3 levels are increasing because the reduction of NO2 emissions is counterbalanced by the increasing role of CH4, the report said.
Globally, 99 per cent of the world’s population is exposed to the harmful effects of air pollution. Global population exposure to O3 increased mainly in southern and eastern China and central Africa, and the annual nitrogen dioxide mean concentration increased in 71 per cent of cities in those regions, it stated.
The authors said the increase in O3 also adversely impacts vegetation and crops, thus affecting ecosystem services and food security.
The report noted that the secondary air pollutant significantly affects vegetation growth, evapotranspiration and water cycle processes, which affect ecosystem functions and services.
“Changes in air quality also cause biodiversity loss due to the effects of different primary and secondary air pollutants. For instance, tropospheric ozone as a secondary air pollutant harms plants and diminishes biodiversity,” it observed.
In 2020, critical thresholds necessary for forest protection were surpassed in 59 per cent of the total forest area of the 32 European Environment Agency (EEA) member nations, it noted.
In two decades (from 2000 to 2020), agricultural land exposed to ozone levels above the protective target for vegetation saw a general decline in the proportion to the agricultural land in EEA Members, reaching a minimum of 6 per cent in 2020. However, in 2019, economic damage incurred from the effects of ground-level ozone on wheat production amounted to €1,418 million across 35 European countries, the report noted.
Such damages can threaten food security.
Meanwhile, the stratospheric ozone layer continues its recovery, contingent upon full compliance with the Montreal Protocol. However, the authors warned that unprecedented wildfires, such as those in Australia (2019-2020), can inject aerosols into the stratosphere and contribute to temporary O3 depletion.