How do we quantify air quality impacts from a new industrial emissions source?

As we approached the turn of the decade, environmental issues became closer to the forefront of public concern, and with that, political concern. The 2020s are set to be the decade of environmental action, and amongst the most pressing and imminent challenges before us Air Quality is high up on the list.

According to the World Health Organisation, poor air quality is responsible for 4.2 million deaths worldwide every year[1]. For plants which operate in the UK, their impacts must be assessed under the Air Quality Standards Regulations 2010, the Environment Act 1995, and the Conservation of Habitats and Species Regulations 2010 – to name a few.

The burning of fuels produce a variety of nasty biproducts which pollute the atmosphere. Nitrogen dioxide (NO2), for example, is a gaseous pollutant which is a primary cause for concern across the globe due to its abilities to cause adverse health impacts on people and damage to ecological systems. In order to ensure minimal impacts from a new emission source, an air quality assessment must be produced by quantifying the impacts using an atmospheric dispersion model.

As with any kind of computer model, an atmospheric dispersion model is a mathematical representation of real-world processes. As such, the model itself can only ever be as accurate and reliable as the data you put into it - and there is a lot of data to put into it.

The following parameters are required before you can begin to quantify the impact of your new emissions source:

• A geo-referenced base map – this allows you to accurately represent your real-world site setting and surroundings in correctly scaled computer version.
• The source(s) of emissions – the location, height and diameter of your stack needs to be put on your map, along with factors such as the temperature and velocity of the exhaust gas, the emission rate and flow rate.
• Terrain – the dispersion of pollutants is highly affected by the terrain of the surrounding ground.
• Buildings – as with terrain, buildings can cause downwash, creating spikes in concentration the side of the building opposite to your emission source. Therefore, buildings within the vicinity of your source must be digitised within your model.
• Meteorology –prevailing wind, wind strength, temperature, pressure and relative humidity are a few of the meteorological factors which need to be considered.
• Receptors – receptors provide a point within the model at which the pollution concentration can be quantified to ensure no adverse impacts occur at a location of relevant public exposure or at a sensitive ecological designation.

Before you can run your model, you also have to define the following:

• The baseline air quality – to quantify what the concentrations will be at your selected receptors when your new emissions source is operational, you need to know what the current concentrations of the air pollutants you’re modelling are.
• The pollutants you need to quantify – this depends on the input fuel. For example, burning natural gas requires NO2 to be assessed. If the input fuel is landfill gas, you would have to assess NO2 and sulphur dioxide (SO2).
• Averaging periods and percentiles – in relation to the air quality standards and objectives which you are assessing against, along with the pollutants you are quantifying.

Only once all these parameters have been defined and loaded into your atmospheric dispersion model can you run the model and quantify the impacts of your new emission source on the surrounding receptors.

The now predicted process contribution (PC) at each of your receptors must be assessed to determine whether the increase in concentrations are significant or insignificant. If it is significant, the impact can be investigated further by looking at the existing baseline.

If the results show that the new source is going to pose a risk to human or ecological health, there would be a requirement to redesign or consider an altogether different location – thereby ensuring the safety of the public and natural ecosystems.

[1] WHO, https://www.who.int/health-topics/air-pollution#tab=tab_1, accessed 26th March 2020.

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