NO2 dissolves in water droplets creating nitric acid in the air and contributing to acid rain. Nitrogen oxides act as precursors for the formation of ground-level ozone which can constitute a health hazard. Carbon Monoxide Colourless, odourless, poisonous gas produced by the incomplete combustion of carbon compounds. Sulphur Dioxide Formed by the oxidation of sulphur impurities in fuels during combustion. In the atmosphere is usually oxidised to form sulphur trioxide, a secondary pollutant.
Sulphur trioxide is very soluble in water, forming sulphuric acid and contributing to acid rain.
Particulates Airborne particulate matter is a mixture of organic and inorganic substances. Other substances, such as dioxins, may need to be batch monitored - once a year say. A gas analyser to measure gas concentrations. A particulate analyser to measure particulate concentration. A computer with a data acquisition interface - perhaps in the form of a card which plugs into an expansion slot of a PC, and provides analogue and digital inputs and outputs.