Non-methane volatile organic compound emissions from malt whisky maturation: final report

Review of the human health and environmental impacts of non-methane volatile organic compound emissions from malt whisky maturation facilities prepared for the Scottish Government by Aether.

5 Environmental impacts

5.1 Ozone formation

Increased concentrations of ozone can be damaging to ecosystems as well as to agricultural crops. Some vegetation may be more sensitive to ozone than others, with effects of excessive ozone exposure including visible leaf injury, increased die-back and reduction in growth and seed production (Global Challenge Network on Tropospheric Ozone, undated; Mills, 2011b). Vegetation damage can impact the entire ecosystem due to interspecies dependence, reducing biodiversity in areas of increased ozone concentration. Cropland damaged due to exposure to ground-level ozone may lead to reduced yields and reduced quality of product, with economic implications for the agricultural sector.

The EU Ambient Air Quality Directive (AAQD; European Parliament and Council, 2008) sets an accumulated ozone exposure threshold value over the averaging period of May to July. This threshold value is based on the sum of hourly ozone values that exceed 80 μg/m3, and is set at 18,000 μg/m3.hour. The AAQD also sets a long-term objective to reduce the exposure of vegetation to low-level ozone to 6,000 μg/m3.hour or less. For forests, the critical ozone exposure level is set by the UNECE Convention on Long-Range Transboundary Air Pollution (CLRTAP) at 5,000 μg/m3.hour (Mills et al., 2017). Although not a regulatory level, this exposure level instead acts as a guide for understanding when critical damage may be occurring due to ozone. Due to reduced light exposure to catalyse atmospheric reactions that produce ozone, much of the forested areas in northern Europe did not exceed the critical level in 2019 (EEA, 2021a). It is worth noting that ground-level ozone concentrations are highly dependent on sunlight exposure and therefore vary year upon year. Some studies, however, have still found evidence of the effects of ozone on vegetation in Northern Europe (Mills et al., 2011a).

Monitoring of ozone concentrations occurs throughout the UK, either through Defra's Automatic Urban and Rural Network (AURN) or by local authorities themselves, as well as across Europe with results compiled and presented by the EEA through the European Air Quality Index. As outlined in Section 4.3, ozone concentrations are typically higher in rural locations than in urban locations. The monitoring and reporting of the measurements taken is focused on assuring that the human health ozone objectives are met, rather than the AAQD for vegetation. In 2021, only one region of the UK, the South West, exceeded the ozone long-term objective for vegetation (Defra, 2022). However, in 2018, a high ozone year, the ozone long-term objective was exceeded at two of the Scottish regions – Highland and Scottish Borders (Defra, 2019). It can therefore be determined that, depending on climatic conditions, ozone has some impact on vegetation in Scotland though the significance of the impact is unclear.

Secondary formation of ozone is NOx limited in the UK, and therefore additional emissions of NMVOC are unlikely to greatly increase ozone concentrations. Additionally, ozone formation is highly dependent upon meteorological conditions, which are likely to have a greater impact on ozone concentrations than the emissions from the Scotch whisky industry. That being said, Scotch whisky production contributes significantly to the total NMVOC emissions in Scotland which may form ozone. Therefore, the impact of Scotch whisky production on the environment as a result of ozone formation is likely to be low.

5.2 Secondary aerosol formation

Formation of both secondary organic aerosols (SOAs) and secondary inorganic aerosols (SIAs) is discussed in Section 4.4.

The presence of SOAs can change atmospheric chemistry and interact with sulphuric acid, but it is unclear how the SOAs produced by Scotch whisky emissions may contribute to this. There is some evidence that SOAs can produce radiative forcing and therefore contribute to climate change (Shrivastava et al., 2017). SIAs can scatter and absorb solar radiation so contributing to climate change, as well as by modifying the properties of clouds (Verheggen, 2010).

As discussed in Section 4.4, the extent to which emissions from the Scotch whisky industry contribute to secondary aerosols in the atmosphere is unclear. Further research is necessary to determine this contribution, and the potential environmental impacts they may cause. However, the environmental impact is assumed to be negligible for both SIAs and SOAs.

5.3 Climate impact

Climate change can affect human health in two main ways: first, by changing the severity or frequency of health problems that are already affected by climate or weather factors; and second, by creating unprecedented or unanticipated health problems or health threats in places where they have not previously occurred (US Global Change Research Programme, 2016).

In addition, many air pollutants contribute to global warming by absorbing energy in the atmosphere and therefore slowing the rate at which energy escapes to space. Some air pollutants have the ability to absorb more energy and hold onto it for longer and therefore they have a greater impact on global warming. The measure of this is a pollutant's global warming potential (GWP).

Little research has been produced as to the GWP of ethanol in particular, however Collins (2002) has conducted research into the indirect GWPs of 10 NMVOCs. None of these are ethanol, but the study does include NMVOCs with similar chemical compositions such as ethane and methanol. This study was the first of its kind but did identify that pulses of short-lived organic compounds can induce perturbations in the tropospheric distributions of methane and ozone that are long-lived and decay on a 10-to 15-year timescale.

Ethanol and acetaldehyde (a secondary pollutant formed from reactions with ethanol) may be involved in reactions causing their complete degradation to CO2 and H2O (Australian Government, 2022). In addition, ethanol can act as a precursor, leading to the formation of photochemical smog. Ethanol may also form methane. This occurs because ethanol is a good nutrient and energy source for microbes who feed upon it. In the absence of oxygen, this can lead to the formation of methane (Australian Government, 2022) thus contributing to global warming.

It is worth noting that the production of CO2 from the evaporation of ethanol will likely be climate neutral. Any CO2 formed through atmospheric reactions with ethanol will be vegetative CO2 returning to the atmosphere without degradation of the land that it originated on. There will therefore only be an additional climatic impact if either ethanol on release has a higher GWP than CO2 or if ethanol degrades into other molecules with a higher GWP than CO2. Many of the secondary pollutants resulting from NMVOC emissions are also greenhouse gases. Tropospheric ozone has a negative effect on plant growth/biomass, which might increase radiative forcing (US National Climate Assessment, 2014). Radiative forcing (RF) quantifies the change in energy fluxes where positive RF leads to surface warming and negative RF leads to surface cooling (IPCC, 2013). Secondary pollutants such as PM are also produced due to the emission of NMVOCs into the atmosphere. PM includes various different pollutants with a wide range of properties – some have a warming effect on the climate whereas others have an atmospheric cooling effect (US EPA, 2022b). The extent of PM derived as a result of whisky maturation is unknown and would require further investigation to determine the climate impact.

A review of the climatic effect of ethanol, and the release of secondary pollutants from NMVOC emissions, indicates there will be a climate impact. It is expected that the extent of impact will be small but is worth noting their contribution. Further research is necessary to determine the exact extent of this contribution, and the potential climatic impacts that NMVOC emissions from whisky maturation may cause.



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