Despite these wide‑ranging differences, air quality and climate change are strongly interconnected. The WMO Air Quality and Climate Bulletin reports annually on the state of air quality and its connections to climate change, reflecting on the geographical distribution of and changes in the levels of traditional pollutants.
Traditional pollutants include short‑lived reactive gases such as ozone – a trace gas that is both a common air pollutant and a greenhouse gas that warms the atmosphere – and particulate matter – a wide range of tiny particles suspended in the atmosphere (commonly referred to as aerosols), which are detrimental to human health and whose complex characteristics can either cool or warm the atmosphere.
Air quality and climate are interconnected because the chemical species that affect both are linked, and because changes in one inevitably cause changes in the other. Human activities that release long‑lived greenhouse gases into the atmosphere also lead to the enhancement of concentrations of shorter‑lived ozone and particulate matter in the atmosphere. For example, the combustion of fossil fuels (a major source of carbon dioxide (CO2)) also emits nitrogen oxide (NO) into the atmosphere, which can lead to the photochemical formation of ozone and nitrate aerosols. Similarly, some agricultural activities (which are major sources of the greenhouse gas methane) emit ammonia, which then forms ammonium aerosols. Air quality in turn affects ecosystem health via atmospheric deposition (the process by which air pollutants settle from the atmosphere to Earth’s surface), which therefore also links air quality to climate. Deposition of nitrogen, sulfur and ozone can negatively affect the services provided by natural ecosystems such as clean water, biodiversity and carbon storage, and can impact crop yields in agricultural systems.
