Several types of industries discharge particulate material into the air.
Examples in Taranaki are milk powder escaping from dryers, particles of metal salts and combustion products within smoke from furnaces, or dust and grit from abrasive blasting facilities. Where these discharges are emitted from a stack or duct, the Council is able to measure the concentration and rate of discharge (mass emission rate) of the particulate matter suspended within the air flow.
In this way, the Council can determine how well air pollution control equipment is working (for example, a cyclone should keep the dust concentration below 200-250 mg per cubic metre, a baghouse below 50 mg per cubic metre), and whether off-site effects such as a visible dust plume or soiling of property may occur.
The particulate is collected on a filter and weighed. If necessary it can then be analysed further, for substances such as silica or for the concentration of potentially toxic metals such as lead or zinc.