Global warming versus pollution: the balancing act

John F. Unsworth (Scientists for Labour)

presented at Scientists for Labour Climate Change - Policy, Science & Strategy meeting,
Westminster, 28 Feb 2001

range of novel vehicles and alternative fuels are expected to be progressively introduced into the UK market over the next two decades. The impact up to 2020 on UK road transport emissions of these novel fuels and vehicles has been estimated by modifying predictions made for the EU Auto-Oil II. Improvements in conventional vehicle technologies from 1990 to 2020 are expected to lead to large reductions in emissions of NO_x and other pollutants, in spite of an increase in vehicle numbers from 27 to 40 million. A steady introduction of novel vehicle and fuel technologies starting in 2005 should lead to further reductions.

On-road CO₂ emissions from conventional vehicles are expected to rise by 14% from 1990 to 2005 and then remain reasonably constant until 2020. The introduction of novel vehicles will halt this increase in CO2 emissions such that by 2020 emissions should be just 1% below the 1990 value. This falls short of the Kyoto overall UK target of 12.5% reduction by 2008-2012 from a 1990 baseline.

Although on-road emissions are the predominant source of emissions, Well-to-wheels Life cycle estimates for the various options need to include all emissions. Extraction, transport, refining, and distribution need consideration, together with cultivation for biofuels, and these emission contributions offset some of the benefit of being "CO₂" neutral during actual combustion. Much variation is evident between different life cycle studies of the same technology, so caution is needed until a clear detailed consensus on assumptions is achieved.

In many cases providing solutions for the CO₂ issue will be inhibited by pollution concerns associated with the technology. Examples are the increased levels of NO_x and particles produced from the more fuel efficient Direct Injection petrol vehicles now becoming available, together with more well-known ones such as dioxin fears from Energy-from-Waste facilities or nuclear power itself.

Concerns about the influence of small particles on general mortality, heart/lung diseases and carcinogenicity has grown in recent years. This has been based primarily on epidemiological studies - there is little clear scientific evidence yet identifying the cause(s). For airborne particles are complex in terms of their origin, composition, size and shape, containing species as chemically different as solid carbon, soluble and insoluble inorganic salts, and a myriad of adsorbed organic species. They may range in size from a few nanometres through three orders of magnitude to the micron level. Furthermore particles may be transformed in size (through agglomeration) or composition (soluble minerals are derived from secondary atmospheric processes) after they have been emitted from the combustion source. This provides considerable challenges to those seeking causes and solutions, nevertheless some progress has been made with the development of catalytic particulate matter traps suitable for diesel vehicles and the supply of the appropriate ultra-low sulphur fuel.

One of the renewable options that provokes the most controversy is Energy from Waste, known better to the general public as incineration. Fear of dioxins descending on the local neighbourhood is sufficient to motivate the formation of local action groups the moment a plan is rumoured. The cause is clear enough, dioxins are unfortunately formed in the same post-combustion temperature regime over which energy recovery is most efficient. Extremely low emissions limits apply which involve detecting femtogrammes (10^-15g) of individual dioxin isomers - surely an analytical triumph in itself. Methods to adsorb dioxins are conventionally used, but unfortunately rarely found coupled with catalytic end-of-pipe fail-safe techniques which destroy dioxins. Sampling and analysing dioxins in stack gases is intricate and consequently expensive (£1000-£2000 per test) and frequently only measured once a year. This, coupled with past failures, and a "cowboy" reputation in operational housekeeping (e.g. indiscriminate use of fly ash in playgrounds or allotments) serves to increase public suspicion.

Perversely for local action groups the major dioxin exposure route is via ingestion (typically 90%) and not via the inspiration of ambient air. In contrast to particles the biological impact of dioxins has been very well researched, and no effect levels estimated for reproductive and immuno-toxicity based on a wealth of experimental data. This leads to recent scientific recommendations to the EU of a recommended maximum daily intake of 1 pg[Teq]^*/kg body weight/day. Average adult exposure is estimated at 0.4-1.5 pg[Teq}/kg/day - clearly no safety margin for any one of us and worse for breast-fed babies of low body weight. But there is no panic, for there are no reported incidences of severe illness associated with dioxin incidents other than chloracne, and little epidemiological evidence to cause sufficient alarm to impose dioxin limits in all our food.

Finally, let us turn briefly to nuclear power - perhaps the quickest way to respond to global warming, but one whose future is severely limited by pollution fears - past, present and future. We should remember that Nuclear still plays a major role in UK electricity production providing 20-22% of the grid over the past five year period. Reductions in UK nuclear power production as occurred in 2000 (loss of Wylfa) led to its substitution by more coal usage and consequently increased CO₂ emissions. Nuclear power will be here for a long time yet, current UK reactors have lifetimes of 20+ years. However until cost-effective and fail-safe solutions are found for plant operation, waste storage and decommissioning, there is little likelihood of any new plants in Europe. Nevertheless other countries in the Far East continue to build nuclear stations. There is no guarantee that the contribution from renewables to the electricity grid will grow quickly enough to satisfy the growing global energy demand. The nuclear option remains available and might yet need to be revived, particularly if research directed at the nuclear waste issue yields some satisfactory solutions.