Previously confined to the factory environment, concern over the hazards of inhalation of potentially toxic substances, has spread out to the home, the office and the street. 

Sources which potentially present a risk of adverse impacts directly on air quality are many and varied including:  

• road (and other) traffic
• mineral workings
• contaminated land workings
• landfill sites
• numerous industrial sectors

As the number of sources broadens, and awareness increases amongst the general public as to the potential impacts on human health, the task of assessing and managing it becomes a more and more complicated exercise. 

Monitoring of air quality is - along with source inventories, source monitoring, and dispersion modelling - one tool available to regulators and industry to help evaluate the environmental impact of atmospheric emissions from current and proposed developments (transport, industrial).

In the absence of useful emission concentration standards for most substances emitted to atmosphere, many companies now undertaking environmental management programmes find perimeter monitoring as an important part of their environmental baseline review.

Monitoring can be carried out by a number of techniques .

In some circumstances it may be useful to monitor local vegetation, for certain chemical species this provides an indication of where levels of contamination (by either gas diffusion, direct deposition or root uptake) are above background levels.