Earth observation data from space is now familiar to the general public, and is very useful in people's daily lives, including weather forecasts and typhoon path predictions. However, we understand that satellite observations of atmospheric composition—observations of chemical substances present in the atmosphere from space—are also useful in monitoring air pollution and climate change, thus contributing to the conservation of the Earth’s environment, yet few people have a systematic understanding of how they are useful for humans. This is because when it comes to global environmental issues, satellite data is not directly linked to the convenience of people’s life, but is first mediated by policy. In this paper, we discuss the complementary roles of satellite observations and ground-based observations in the overall air quality observations, environmental policy, with the main focus on the satellite observations of nitrogen oxides, which is the main precursor of ozone and PM_2.5. We also describe the unique roles of the latest satellite observations, including Japan’s GOSAT-GW (Global Observing SATellite for Greenhouse gases and Water cycle) satellite to be launched during fiscal year 2025, for air pollution control policy.

The cause of uncertainties in air quality simulations using the CMAQ regional chemical transport model remains unclear. One possible cause is the uncertainty in the emission inventories used as inputs to the CMAQ. This study aims to provide valuable information about the uncertainty in the CMAQ by a box model approach of an air quality simulation that does not rely on emission inventories as the inputs. A box model air quality simulation was conducted in the Tokyo urban area based on the measured concentrations of volatile organic compounds (VOCs). The simulation showed a good reproducibility of the ozone concentrations, indicating the model’s usefulness in assessing the CMAQ uncertainty. The box model simulation suggested that the reproducibility of the CMAQ background ozone concentrations is a factor that influences the CMAQ ozone overestimation. Estimates indicated that the current VOC emission inventories may underestimate the emissions, except for aromatics. Formaldehyde is a significant contributor to high ozone concentrations with both direct emissions and secondary formations equally responsible for its formation. The study estimated the VOCs that significantly contribute to the formaldehyde formation. Reducing these formaldehyde precursors resulted in a significant amount of ozone reduction. These findings indicated that reducing the formaldehyde precursors is important in preventing harmful levels of ozone.

A study was conducted to investigate the concentrations of ammonium sulfate ((NH₄)₂SO₄) and ammonium bisulfate (NH₄HSO₄) in ambient particulate matter (PM_2.5) at a single location in Tokyo over a one-year period, from August 2022 to August 2023. Following 52 consecutive weeks of one-week samplings, the detection rate of (NH₄)₂SO₄ was 100% with the annual average concentration of 1.2 µg/m³. Its maximum concentration was 3.8 µg/m³. The annual concentration of the (NH₄)₂SO₄ trends were higher during the spring and summer (March to August) and lower during the fall and winter (September to February). The detection rate for NH₄HSO₄ was approximately 27% with an average concentration of 0.6 µg/m³, and the detection period was from April to August. Also, an analysis of the relationship with air pollutant concentrations showed a correlation with the oxidants.