Carbon dioxide, or CO2, is an important greenhouse gas linked to global warming. CO2 comes from the extraction and burning of fossil fuels (such as coal, oil, and natural gas), from wildfires, and natural processes like volcanic eruptions.
Nitrogen dioxide, or NO2, is a gaseous air pollutant composed of nitrogen and oxygen and is one of a group of related gases called nitrogen oxides, or NOx. Nitrogen dioxide forms when fossil fuels such as coal, oil, methane gas (natural gas) or diesel are burned at high temperatures. Nitrogen dioxide causes a range of harmful effects on the lungs, including increased inflammation of the airways, worsened cough and wheezing, reduced lung function, and increased asthma attacks, among others.
Particle matter (PM) is made up of tiny particles of solids or liquids that are in the air. These particles may include dust dirt, soot, smoke, or drops of liquid. Bigger particles, called PM10, can irritate your eyes, nose, and throat. Dust from roads, farms, dry riverbeds, construction sites, and mines are types of PM10. Smaller particles (e.g. PM2.5, PM1), are more dangerous because they can get into the deep parts of your lungs — or even into your blood.
Relative Humidity refers to the percentage of water vapor in the air at a given temperature, compared with water vapor that the air is capable of holding at that temperature. When the air at a certain temperature has all the water vapor it can hold at that temperature, the relative humidity is said to be 100%.
Air temperature is a measure of how hot or cold the air is. It is the most commonly measured weather parameter. More specifically, temperature describes the kinetic energy, or energy of motion, of the gases that make up air. As gas molecules move more quickly, air temperature increases.