NO2 is a product of combustion. It is a precursor to ground-level ozone formation through photochemical reactions involving VOCs. NO2 causes a brown colour in the atmosphere at elevated concentrations. It reacts in the atmosphere with ammonia to form fine particulates, which reduce visibility and increase concentrations (Levelton Engineering Limited, 2000). NO2 irritates the mucous membranes in the respiratory tract. It impairs lung immunity mechanisms, increasing susceptibility to respiratory infections, especially in children and asthmatics, and reduces lung function at high levels. Asthmatics exposed either simultaneously or sequentially to NO2 and an aeroallergen have an increased risk of.
