For many emissions to atmosphere, especially from small industrial and commercial sites, material which is allowed to escape into the atmosphere is, in effect, free disposal.
For example, solvents from a small scale painting process are allowed to evaporate into the atmosphere. The material can add to problems with local air quality, especially in certain weather conditions, perhaps contributing to smog or an odour nuisance. The polluter who released the material gets rid of a polluting waste material without paying for its disposal. Society at large and the site’s immediate neighbours in particular, pay a price – degradation in the quality of their environment.
In recent years, legal controls have been introduced which capture all but the smallest of such processes. But it is a complicated picture: the controls apply to a variety of processes and the extent to which they apply depends on the size of the process.
This guide gives some indication of the types of legal regimes which apply to different types of premises and processes. More detailed information can be found in EEF’s Register of Environmental Regulations in the chapter on air pollution and your local EEF office will be able to help you with practical advice and training (see climate change and fossil fuels).
Fugitive emissions
Many processes release airborne contaminants which escape through doors, windows or vents into the atmosphere. However, in some cases, local exhaust ventilation (LEV), installed for health and safety reasons (see emissions overview and the hazardous substances chapter in the Health and Safety guide) removes gases which are harmful to health out to the atmosphere. This diverts a fugitive emission out through a duct (see ducted emissions below).
Fugitive emissions are difficult to measure. It is good practice to begin with estimating the emission by use of mass balance techniques. If the quantity of material going into the process is known and the details of the process itself are thoroughly understood, then the approximate quantity of emissions can be identified. More detailed measurements using sampling and analytical techniques may then be used (see emissions to air).
Ducted emissions
Many processes release pollutants to the air via chimneys and ducts. In most cases, the release of pollutants is necessary for the operation of the process operating below, e.g. in a combustion process, a chimney is vital to remove products of combustion so that the reaction can continue.
Ducted emissions are easier to quantify than fugitive emissions. As long as there is a means of measuring the following:
- detecting the emission in situ or extracting a representative sample for analysis;
- measuring the velocity of flow in the duct;
- calculating the cross-sectional area of the duct; and
- data on times of operation.
Given the results from these measurements, it should be possible to calculate the emission concentrations and mass emission figures over time.
All of the above emissions can be in the form of gases, fumes (fine solid particles which form in the air) such as welding fume, or vapours and fine droplets of liquid (e.g. oil mists).
Minimising emissions to air
The most desirable option would be to avoid creating the potential in the first place, e.g. using a water-based paint instead of a paint which includes an organic solvent.
Failing that, the polluting material could be captured in the ventilation before it escapes, e.g. organic solvent vapours can be adsorbed onto activated carbon filters. However, this may result in the creation of solid waste when the filters need to be replaced.