The most important primary air pollutans are particulate matter, sulfur oxides, carbon monoxide, hydrocarbons, and nitrogen oxides. Primary air pollutants can undergo chemical reactions within the atmosphere and produce new substances known as secondary air pollutants . The photochemical smog and ozone are the most important secondary air pollutants. Both are generated as a result of interaction between the intense sunlight and the primary pollutans. Smog is the combination of fog and smoke.
Volcanic eruptions are the primary source of gases of the Martian atmosphere.
There are no photosynthesis, and hence, no free oxygen in the Martian atmosphere. Through the early part of the twentieth century, weather intruments borne by kites, aircraft, and balloons provided information about the lowest 5000 m of the atmosphere followed by rockets, radiosondes, satellites, and radar. It provides vertical profiles of air temperature, pressure, humidity, and wind. Dropwindsondes were developed to obtain soundings over oceans. Surface launched rockets that provided information at altitudes of 110 to 165 km was replaced by satellites which monitor patterns of temperature and water vapor concentration, upper-air winds, and the life cycles of severe storms.