Now and then, we come across news about damage to the Earth’s ozone layer. But do we actually know what the ozone layer is, and how damage to it affects us and our environment? Ozone (O3) is a highly reactive gas made up of three oxygen atoms bonded together. It forms a concentrated layer in the Earth’s stratosphere, and at any point of time, they are constantly formed and destroyed in the stratosphere. The ozone layer filters out harmful ultraviolet rays which could cause diseases such as skin cancer or cataracts. On the flip side, if ozone is present closer to the ground level, it can result in adverse effects for humans as well as other living creatures when inhaled.
Ozone production accelerates under higher temperature conditions, resulting in an increase in the emission of natural components of ozone. However, ozone formation is suppressed when the temperature exceeds a threshold temperature (cutoff temperature – Tx). This cutoff temperature varies with cities, ranging from 25.0 ℃ to 40.4 ℃. Statistics show that around 19% of cities in China exhibit the significant suppression of ozone formation at extremely high temperatures.
Associate Professor Steve Yim
In a recent study, NTU Asian School of the Environment (ASE) Associate Professor Steve Yim examined the ozone-temperature relationship in China to reveal the behaviours of ozone suppression, in which they can project and quantify the responses of future ozone to climate warming in the 21st century under different Shared Socioeconomic Pathway* (SSP) emission scenarios.
*SSPs are scenarios of projected socioeconomic global changes up to 2100, which can be used to derive the emission of greenhouse gases according to various climate policies.
“According to traditional understanding, ozone concentration strictly increases with temperature. This relationship is questioned in high ambient temperature environment,” said Assoc Prof Yim. Surface ozone is projected to be suppressed more and up to 11.75% of future regional ozone in high-emission scenarios in the late 21st century.
This is the first study that analyzes the observations of ozone concentration and daily maximum temperature in a total of 329 prefecture-level cities in mainland China from 2015 to 2019. From the data, the scientists built a hybrid model incorporated with ozone suppression to project future ozone concentration during the years 2020-2100 under the historical, SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5 scenarios from 22 climate models’ projection provided by the Coupled Model Intercomparison Project Phase 6 (CMIP6).
Assoc Prof Yim added, “While our current attention focuses on mitigating the projected rising temperature, ozone is overlooked and will increase due to the reduction in temperature. Our study pinpoints the need for more stringent emission controls and co-benefit policies to alleviate future climate change and O3 pollution.”
As of now, ozone suppression is not included in the current future air quality projection; it is essential to incorporate ozone suppression into future ozone projection to better reflect the non-linear relationship of O3 and temperature, especially under the influence of climate change.
Past research has reported 3.2 million mortalities due to air pollution in Southeast Asia. While air pollution is one of the critical environmental issues in Southeast Asia, our understanding about ozone pollution in the region remains limited due to the lack of air quality measurements, substantial emissions, urbanization and the complexity of the atmospheric chemistry and climate dynamics.
Assoc Prof Yim’s team is devoted to understanding this complicated air quality problem in Southeast Asia, especially local ozone formation and transboundary air pollution, and to evaluate the human health impacts.
Read the full paper here.