Air Quality

Air Quality Parameter	Definition	Calculations
Aerosol Optical Depth	Aerosol Optical Depth (AOD) is the measure of aerosols (e.g., urban haze, smoke particles, desert dust, sea salt) distributed within a column of air. Dimensionless quantity	τ = ∫α(z)dz, α here stands for aerosol extinction coefficient at height
Angstorm Exponent	It is used to infer the aerosol particle size distribution within a cloumn of air.	α=−ln(τλ1/τλ2)/ln(λ1/λ2) λ1 and λ2 two different wavelenghts in m.
UV Index	UV Index widely used parameter to characterize solar UV. Information about it can be useful for helping people avoid excessive levels of UV radiation.	UVI=Eeff/25mW/m2, Eeff= effective UV irradiance
Particulate Matter (PM)	Particulate Matter a combination of soild particles and liquid droplets present in the air composed of both fine and coarse particles. Coarse particles (PM10) have an aerodynamic diameter between 2.5µm and 10µm. Fine particles have an aerodynamic diameter less than 2.5µm (PM2.5). Units µg/m3.	PMx=Mparticles/V air, Mparticles= mass of collected particles (micrograms, µg), V
NOx	NOx, or nitrogen oxides, refers to a group of gases that include nitric oxide (NO) and nitrogen dioxide (NO2), which are significant air pollutants. Units ppb	NOₓ = NO + NO₂
SO2	SO₂ (Sulfur Dioxide) is a gaseous air pollutant consisting of sulfur and oxygen, primarily produced by combustion of sulfur-containing fuels (like coal and oil) and industrial processes. Units ppb	SO2 (concentration) = mass of SO2 (µg)/ Volume of air sample (m3).
CO	CO is the amount of carbon monoxide in the air, which can be harmful because it binds with hemoglobin in the blood, reducing oxygen transport in the body. Units ppm	CO (concentration) = mass of CO (mg)/ Volume of air sample (m3)
O3	A secondary pollutant, formed by photochemical reactions between NOx and volatile organic compounds (VOCs) in sunlight. ppb	O3 (concentration) = mass of O3 (µg)/ Volume of air sample (m3)
VOCs	Volatile Organic Carbon (VOC), more commonly called Volatile Organic Compounds (VOCs), refers to a large group of organic chemicals that easily evaporate at room temperature and contribute to air pollution.	VOCs (concentration) = mass of VOC (µg)/ Volume of air sample (m3)
Visibility	Visibility is the maximum distance at which a prominent object can be seen and recognized in the atmosphere under prevailing conditions of light and air clarity.	V = 3.912/σ, σ = atmospheric extinction coefficient (1/m)
Surface Albedo	Surface albedo is the fraction of incoming solar radiation (shortwave radiation) that is reflected by a surface back into the atmosphere, without being absorbed. Dimensionless	Albedo = Reflected solar radiation/Incoming solar radiation