The troposphere comprises the lowest layer of Earth's atmosphere, stretching from the planet's surface to a little over eight miles into the sky. It also contains about 10% of the ozone in the atmosphere, but that 10% is heavily influenced by human activity and plays a critical role in the formation of smog, which is hazardous to human health, according to an international team led by researchers with the Chinese Academy of Sciences (CAS).
The team recently assessed current abilities to monitor tropospheric ozone, summarizing progress and challenges and proposing new paths forward. They published their review on Aug. 2 in the Journal of Remote Sensing.
Ozone in the troposphere is primarily generated by nitrogen oxide and volatile organic compounds — both byproducts of human activities changing the climate, such as burning non-renewable fuels, the researchers said. Ozone is also associated with weather processes and can cause respiratory diseases, similar to particulate matter 2.5, another pollutant associated with climate change.
Currently, to monitor concentration levels and variations of ozone in the troposphere, researchers either directly measure ozone in specific areas on the surface of the planet or use sensors that can detect the gas at a distance. Using these sensors, typically affixed to satellites or airplanes or weather balloons, is known as remote sensing. While direct measurements are accurate, they lack comprehensive inclusion of atmospheric properties. Similar to taking the temperature of a specific rock, the temperature might be accurate, but it doesn't provide information about the surrounding environment. After all, the rock could've been in direct sunlight on a snowy tundra.
"We reviewed the current observation techniques and retrieval algorithms, analyzed their development trend and identified areas needing improvement," said co-corresponding author Jian Xu, professor with the National Space Science Center, CAS. "Our goal was to highlight the limitations of existing methods and propose a few potential technological solutions for more accurate remote sensing of tropospheric ozone from space."
According to the researchers, remote sensing remains the best way to monitor ozone. Instruments, including various types of sensors, and data processing techniques have significantly improved and will continue to do so. Co-corresponding author Husi Letu, professor with the Aerospace Information Research Institute, CAS, noted better instrument calibration and standardizing analysis approaches would also help advance the field.
"Recent advancements in satellite observation techniques and retrieval algorithms for tropospheric ozone have significantly improved in terms of product accuracy and spatial resolution/coverage," Letu said. "These developments are essential for better air quality management and effective pollution control, highlighting the importance of continued innovation in this field."
The researchers also recommended that future approaches should implement and refine combined active and passive sensing, integrated physics and machine learning retrieval algorithms.
Other authors affiliated with the National Space Science Center are Zhuo Zhang, Lanlan Rao, Gegen Tana, Wenyu Wang, Shuanghui Liu, Entao Shi, Yongmei Wang, Xiaolong Dong and Jiancheng Shi. Rao, Tana, Wang, Liu, Dong and Jiancheng Shi are also affiliated with the Key Laboratory of Microwave Remote Sensing, while Zhang, Entao Shi and Wang are also affiliated with the Beijing Key Laboratory of Space Environment Exploration and the Key Laboratory of Science and Technology on Environmental Space Situation Awareness. Wang is also affiliated with the School of Astronomy and Space Science and Dong with the School of Electronic, Electrical and Communication Engineering, both with the University of CAS. Yapeng Wang, National Satellite Meteorological Center, China Meteorological Administration; Chong Shi and Liangfu Chen, Aerospace Information Research Institute, CAS; and Songyan Zhu, School of GeoSciences, University of Edinburgh, also contributed.
The National Natural Science Foundation of China, the Open Fund of Innovation Center for FengYun Meteorological Satellite, FengYun Application Pioneering Project and the National Civilian Space Infrastructure Project supported this research.
