12 January 2017

Something in the Air: The Insidious Challenge of Air Pollution

Professor Carolyn Roberts

Good evening everyone, and welcome both to Gresham College and to online watchers and listeners. Tonight, I am going to talk about air pollution, one of the most insidious challenges that bedevils all of us, environmental scientists included, this century. I am not going to be talking tonight about greenhouse gases and climate change (at least not directly) but about some of the other chemicals that human activity releases into the atmosphere, and which we may then breathe, or which adversely affect ecosystems and the built environment.

The story of air pollution management in the UK and elsewhere could be told as one of great success. Seventy years ago there were some major problems in our cities. Those old enough to recall the choking London pea souper fogs of the 1950s and earlier will know that since the UK Clean Air Act was passed in 1956, and sulphurous coal and wood fires were banned in city areas, visible black smoke has almost disappeared. In fact, there was a lot of opposition to the ban at the time, since domestic coal fires were seen then as a powerful symbol of post-War British prosperity, whereas today it is probably the size of the TV screen that designates relative wealth and comfort. Each has their environmental impact, of course. The slide shows the additional 3- 600 deaths per day in London that occurred over several days in December 1952 when wind-speeds were low, temperatures cold, and open fires were common in the capital. The coal-fired Bankside A Power Station, now the site of Tate Modern, was then depositing an estimated 235 tons per square mile of so called grit in the area during the month of September 1950 (as measured by London County Council) which is probably not a coincidence. Coal-fired power stations have also almost disappeared in our cities.

Internationally, there have been some successes as well. Through the 1987 Montreal Protocol for example, we have addressed the long-lived, atmospheric chlorofluoocarbon (CFC) emissions from refrigerants, dry cleaning fluids, aerosols and packaging materials that eroded a hole in the Antarctic ozone layer. CFCs are manufactured organic compounds containing carbon,fluorine and chlorine (often known as the Devils Element),commonly known by theDuPontbrand nameFreon. The fact that stratospheric ozone protects humanity and other life from harmful incoming ultraviolet radiation had been known for decades, but its sudden depletion as a result of chemical interaction with CFCs (involving NOx gases too) was discovered only in 1985 by three scientists from the British Antarctic Survey, in Cambridge - Farman, Gardiner and Shanklin. As with many natural environmental components, the Antarctic ozone hole swirls and pulsates, growing and shrinking annually and responding to natural ozone variability as we see in the video clip here; that can make evaluation of longer term trends challenging. In fact initially, the satellite observations of low Antarctic ozone levels were through to be erroneous, and the extent of the damage only became apparent after instruments were recalibrated using ground-based observations. A similar but less marked depletion of ozone has occurred in the cold polar clouds of the Northern hemisphere too, as CFC use has dropped.

The scientists were initially vilified by the sellers of CFCs, but international agreement on a ban nevertheless took place very quickly indeed. Some time was required to develop replacement refrigerants and coolants, and there is still some CFC smuggling into developing countries, but banning their use has been a good start and I do not think they are much missed now. The problem is actually not yet entirely solved as the hole is not expected to heal fully until 2060, and in fact it was at its greatest extent in 2015 because of a volcanic eruption in Chile. But the power of international negotiation towards a common goal was demonstrated despite the short term economic cost a positive message. Professor Susan Solomon, who alongside a group from Leeds University leads an MIT team, notes that the precise lesson on collaboration is less than clear. On the pessimistic side, it might be said that a modest-sized global environmental problem can be solved by the world, while a mega-sized one is another matter entirely. This was a chemical industry whose value was measured in the billions, not the trillions of pounds that is tied up in climate change-related companies in the energy sector. But there is still some cause for optimism.

To take another example, in the 1980s and 90s environmental researchers and even politicians in developed countries talked a great deal about acid rainfall: sulphur dioxide and nitrous oxides that had entered the atmosphere from industrial smokestacks and power stations and been washed from the atmosphere downwind by rain and snow, or had fallen as a gentle shower of caustic dust. Even today, occasional rain and fog pH readings of below 2.4 are reported in industrialized areas; that is about the same level of acidity as undiluted Coca Cola (Pepsi seems to be slightly less acidic!), and you will know what that does to human teeth. The acidity created such excesses of hydrogen ions in soils and lakes that it killed trees either directly, or by allowing metals such as lead and mercury to be released into solution. Scandinavian forest and moorland ecosystems were particularly vulnerable and suffered from the UKs acid rain emissions, but European protocols were developed from the 1980s requiring scrubbing technology to be installed in smokestacks. This had demonstrable transboundary benefits to ecosystems and fish over the succeeding years. The reductions in the use of coal, in 2016 providing less electricity in the UK than wind power for the first time (and none at all in May 2016), is a more recent contributory factor as well. The USA has had a similar experience, following legislation enforced by the US Environmental Protection Agency.

Sulphur dioxide emissions also increased the erosion rate of materials in our historic buildings and monuments. At St Pauls Cathedral, for instance, investigations showed that exposed Portland limestone had often decayed to a powder under a thin and dirty skin of harder stone. Surface erosion rates between 1710 and 1980, the really dirty period for London smogs, were roughly double what they are now. Sulphur dioxide levels have fallen dramatically over the 30 year period since the monitoring began, and today are at low levels of about 3 parts per billion, a fall of about 95% since the early 1980s. This fall mirrors the situation across Europe, and no European cities are now above the sulphur dioxide limit values set by the EU. So, thats another international success story for managing atmospheric pollution.

However, despite these triumphs, and I could also have talked about removing lead from vehicle fuel, some serious problems persist. On October 2016, the morning after last years Diwali celebrations, the Indian city of Delhi was encompassed in a huge bubble of smog made up largely of tiny particles and droplets of carbon (classified as PM2.5, or less than 2.5 microns in diameter) in concentrations sufficiently high to cause eye and throat irritation, and to penetrate human lungs and enter peoples bloodstreams. On a day when winds were slowing after the monsoon, firework residue was added to the normal atmospheric load of car exhaust, road dust and smoke from open fires, causing the monitor at the US Embassy to record a PM2.5 figure of 9999 g/m3; the safe legal limit for India is 60. Before we dismiss this as something bad but far away, note that an air quality monitor in Farringdon, only 500 metres from where we are tonight in Holborn, recorded a PM2.5 figure of 139 g/m3 on the same day. I will return to London in a few minutes.

Some of these smoke-related air pollution episodes are so large and intense that they are visible from space. Research by NASA in the second half of 1997 showed particles from burning Indonesian trees and peat remaining stagnant over Southeast Asia, while tropospheric, low-level ozone contamination spread more quickly westwards across the Indian Ocean towards India. Ozone is toxic to humans, despite its benefits high up in the stratosphere. These intricate atmospheric circulation patterns are likely to change in the face of climate shifts too, particularly changes to the intensity and timing of El Nio, which alters the date at which wet season starts and fires are damped down. It makes for complexity in the science.

Like low level ozone, other contaminants are also invisible to the naked eye but detectable by specialist monitors carried on satellites, as this very recent NASA video on nitrogen dioxide indicates. I am wondering whether NASA might rather regret broadcasting the last few moments showing the link between recent increases in nitrogen oxides and increased fossil fuel extraction, given incoming President Trumps personal and family interests in promoting oil, gas and fracking; NASA is very reliant on public funding.

There are very recent acute incidents too. A red alert in late December 2016 prompted the closure of factories in many northern Chinese cities, the grounding of flights and limits on the number of cars to reduce pollution. Authorities in Beijing temporarily suspended operations in 700 companies, and hospitals experienced a major spike in admissions for air pollution-related illnesses and breathing difficulties, especially amongst children. The pictures here tell the story, as reported by the Daily Mail, Reuters and many others. This is a typical situation for many megacities in the developing world, whether or not the atmospheric pollution is actually visible, although often it is (nitrogen dioxide is a