NASA: “The Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument collected its “first light” measurements of nitrogen dioxide air pollution over North America on August 2, 2023. Beginning at 11:15 AM Eastern Daylight Time (8:15 AM Pacific Time), the instrument scanned the continent every hour for six consecutive hours. TEMPO measures sunlight reflected and scattered off the Earth’s surface, clouds and the atmosphere. Gases in the atmosphere absorb the sunlight, and the resulting spectra are then used to determine the amounts of several gases in the Earth’s atmosphere, including nitrogen dioxide. The amount of nitrogen dioxide is provided as a “column density”, defined as the total number of nitrogen dioxide molecules in a column of air above a square centimeter on the Earth’s surface. The tropospheric column density is the amount of nitrogen dioxide in the lower part of the atmosphere, from the surface to about 10 km in altitude. In polluted regions, most of that nitrogen dioxide is located near the ground. In North America, nitrogen dioxide is primarily produced from burning fossil fuels for transportation, power generation and industrial activity, as well as from wildfires. Nitrogen dioxide plays an important role in the formation of ground-level ozone and particulate matter pollution, and is itself a toxic gas. These pollutants are harmful to both human and ecosystem health. TEMPO makes measurements of the atmosphere with unprecedented resolution in both time and space. Previous satellite instruments have measured air pollution from low-Earth orbit, passing over a given location on the ground once per day. Because TEMPO is in a geostationary orbit, the instrument can continuously observe North American pollution during daylight hours. This allows TEMPO to capture changes in emissions, chemistry and transport over the day, enabling better knowledge of pollution sources and population exposure to poor air quality.”