pollution
December’s winds dispersed urban air pollution and January wafted in a new air quality index
A windy December was good news for air pollution. Urban air pollution was rapidly dispersed and low air pollution prevailed across the UK.
The new UK daily air quality index was launched on 1 January. Like the indices for pollen and UV, it aims to condense scientific information into an easy to understand format. When fully implemented, real-time changes in air pollution will give advance warning of problems, helping people to act to protect their own health. Daily air pollution is graded as low, moderate, high and very high with specific advice for vulnerable adults and children, such as those with heart and lung conditions. This includes advice on the use of their asthma inhalers or reducing their outdoor exercise when air pollution rises.
When air pollution reaches high or very high even generally healthy people may also experience symptoms such as cough and sore eyes or throat, and some athletes may notice effects during high levels of summer-time smog. New evidence means that more days will be described as having moderate or high air pollution, especially in towns and cities and close to busy roads.
Helping vulnerable people to protect their health is undoubtedly sensible but it is likely that lifetime exposure to even low levels of air pollution causes a greater health burden. This requires decreases in emissions from industry and transport every day, and not just action when air pollution is high.
London experienced its first wintertime smog of the season last month when the settled weather that led to fog delays at Heathrow also caused pollution problems across the capital. As air drifted very slowly across London between 20 and 22 November it accumulated pollution, creating a clear gradient across the city; moderate airborne particles were measured in the west and northern suburbs while air pollution remained low on the other side of London. Although pollution from traffic was a major cause, unusually the greatest pollution was not measured during rush hour but occurred in the late afternoon and evening of Sunday the 20th when many people would have been at home.
This raises interesting questions about the contribution of pollution from domestic heating, and most especially the renewed popularity of open fires. Big cities are vulnerable to wintertime smog. The Paris authorities declared pollution alerts between 21 and 23 November and Berlin had pollution problems on 12 days during the month.
Earlier in November widespread pollution problems from Guy Fawkes fireworks across the north-west of the UK were followed by a flow of polluted air from Europe. This added to local traffic pollution in towns to cause moderate airborne particles in urban areas across eastern England: in London, Norwich, Scunthorpe and Sheffield on 8 November spreading north to Leeds, York and Newcastle upon Tyne on 9 November.
Smoke from fireworks and bonfires means that 5 November is often the most polluted night of the year. This year damp and breezy weather in southern England meant smoke was rapidly dispersed, but this was not the case in the northern half of the UK. The government’s banding system divides air pollution into low, moderate, high and very high, according to its potential health effects. Smoke from Guy Fawkes’ events caused greatest problems in north-west England where air pollution levels reached very high in Stoke and Salford and high in Warrington. High air pollution was also measured in Birmingham, Glasgow and Grangemouth. In late October Diwali fireworks also caused pollution peaks across the London suburbs, and in Southampton, Reading and Liverpool.
Recent studies have highlighted the use of toxic metals in fireworks. Metals are used as propellants, to shoot fireworks into the air, and to create the sparkles and colours including red (strontium), green (barium), blue (copper), silver (aluminium and titanium), purple (copper and strontium) and gold (iron). Pollution from Guy Fawkes’ events this year lingered in northern UK cities until late the next morning, up to 18 hours in places. Studies of the Sant Joan fireworks in Gerona, Spain, showed that toxic metals from just two hours of fireworks can persist in city air for four days. Fireworks are great fun, but is the toxic cocktail worth the show?
The heat-wave at the end of September also brought unwelcome summertime smog to the UK and set a new pollution record for October. Moderate levels of ground level ozone extended as far north as Fort William on 28 September and many areas broke World Health Organisation (WHO) guidelines. Before reaching the UK, the warm air spent two days crossing France, collecting pollution en route. The greatest pollution problems occurred in major cities where traffic added to the imported smog.
A pollution alert for nitrogen dioxide was declared in Paris on 29 September. On the same day London also experienced problems with nitrogen dioxide and airborne particulates, which continued for four days until 2 October. Fresher Atlantic air reached Northern Ireland and Scotland first and then pushed over the whole UK, finally clearing the summertime smog from London and the south-east on 4 October.
Summertime smog is very unusual at this time of year. Analysis of pollution between 2000 and 2009 around London suggests that the chances of breaching the WHO guidelines for ground-level ozone are normally less than 5% during the last week of September. Summer measurements of ground-level ozone began in Harwell, Oxfordshire, in 1976 and measurements for October extend back to 1984. The ground-level ozone at Harwell this year set a new October record, beating the previous one set in 2005.
One of London’s longest running air pollution monitoring sites was at the heart of the rioting that began on Tottenham High Road on Saturday 6 August. The intensity of the fires meant that much of the smoke was lofted away from the immediate area; however, the monitoring site measured two hours of pollution that was around 10 times greater than average. Interestingly the air pollution was not just the small particles typical of smoke but it also contained many larger particles, presumably owing to dust from falling debris as fire damaged buildings began to crumble.
The fire at Reeves furniture store in West Croydon on the evening of Monday 8 August was shown live on news programmes. Flames leapt into the sky and could be clearly seen over 8kms away. Once again the heat from the fire lifted the smoke high. A gentle westerly wind carried smoke before it came to ground around 600 metres away in East Croydon at around 9pm. Here air pollution reaching around 20 times average levels was measured until early the following day. Although the fires caused large air pollution peaks the UK health guidelines, based on exposure averaged over the whole day, were not exceeded.
Warm weather at the start of the month caused moderate ground level ozone over the southern half of England, reaching as far north as Birmingham, Nottingham and Leicester, but generally unsettled weather prevented serious summertime smog.
July has been a good month for air pollution, in contrast to previous years when the month has been a peak period for summertime smog. Brief periods of moderate ground-level ozone affected most of southern and eastern England, and warm weather at the end of the month caused moderate ozone to extend over Wales. Grangemouth, central Scotland, experienced pollution problems from the nearby steelworks but otherwise air pollution remained low.
The UK air pollution index divides peak air pollution concentrations into low, moderate, high and very high to help vulnerable people cope with the immediate health risks. The deaths of more than 4,000 people in the London smog of 1952, and those that followed, taught us that air pollution peaks had a major public health impact.
However, as our understanding of air pollution evolved from the 1990s it became clear that long-term exposure to low levels of pollution have a far greater health impact than short-term peaks. It is therefore of great concern that the UK and countries throughout Europe are struggling to comply with annual limits for particulate pollution and nitrogen dioxide.
The UK recently obtained more time to comply with EU limits for particulate pollution, which were originally set for 2005. The government now estimates that nitrogen dioxide limits set for 2010 may not be met in 16 major urban areas until 2015 to 2020, and after 2020 in London: 21 years after these limits were passed into law.
Although temperatures at the end of June were the highest for five years (33C in Kent) there was no repeat of the pollution problems that we experienced at Easter. Hot weather began on Sunday 26 June, but a fresh Atlantic air feed meant that pollution stayed low. Air over eastern England on Monday 27 June was more polluted, having spent Sunday over France.
Moderate levels of ozone were measured across eastern England including the south-east, the east Midlands and parts of Yorkshire, but two factors enabled us to avoid serious smog. First, relatively low traffic levels and industrial emissions over France on Sunday meant there was insufficient pollution to form smog over the UK on Monday. Second, summertime smog does not form quickly; it can take two or three days for hot sunlight to drive the chemical reactions between air pollutants that lead to harmful levels of ozone and airborne particles. In this case, there was insufficient time for the smog to form before the polluted air was pushed eastwards as violent thunderstorms spread across the UK on Tuesday, 28 June. The residents of Paris were not so lucky, and the heat wave caused the city authorities to declare a surprise pollution alert.
Earlier in June, sunny spells caused brief moderate ground level ozone across many parts of the UK. Grangemouth, Fife, experienced sulphur dioxide problems from nearby industry on three days in mid June.
Ash from the Grímsvötn volcano appeared in Aberdeen soon after midnight on 24 May. The main ground-level impacts were measured across Northern Ireland around breakfast time and then spread eastward.
By late morning ash was detected in the north-west of England from Carlisle and Blackpool through Preston, Cheshire, Merseyside and Greater Manchester to as far south as Stoke. By lunchtime it had spread east to York, Leeds, Sheffield, Hull, Chesterfield and south to Nottingham.
The mineral content of airborne particles is not routinely measured in the UK but a number of factors point to volcanic ash as the cause of the air pollution on the 24th. Firstly, air can be traced back to the vicinity of the volcano some 48 hours earlier and a wide area of the UK was affected at the same time, consistent with a distant source.
Secondly, the sampled particles were unaffected by gentle heating during analysis, they were far larger than those from transport and industry and did not contain soot, which normally arises from combustion sources. Particles from the volcano affected each area for four to six hours and caused pollution levels similar to those often experienced by busy roads, or near building sites.
Although most of the UK experienced some moderate ground-level ozone during May, a return to Atlantic airflows and cooler weather prevented a repeat of Easter’s pollution and provided some respite from the airborne particle problems that have plagued London and the south-east since mid-February.
The government’s smog warning on 21 April heralded the worst air pollution of the year so far. The UK describes air pollution as low, moderate, high or very high according to the health risk. Over the Easter weekend airborne particles reached high in Leeds, London and towns in Essex and Kent. Moderate levels were measured throughout England and Wales. Excluding Guy Fawkes, this was the worst air pollution since 2007. Strong spring sunshine and hot temperatures also caused air pollutants to react together leading to widespread moderate ozone over most of the UK and high levels in London and Manchester.
This year the fresh westerly air flow that normally brings March winds and April showers was replaced by easterly winds bringing a record breaking dry March, warm April and polluted air from Europe. No part of UK escaped moderate air pollution during May; moderate ozone reached Lerwick, Shetland, and moderate ozone and airborne particles reached Northern Ireland. Throughout Europe air pollution is caused by the combination of local traffic and industry along with pollution blown from farther afield. In the last decade airborne particle levels from Europe have decreased faster than pollution from road traffic in our cities; levels of pollution reaching the UK from Europe over Easter were around half those during the peaks in 1996, but this Easter shows the need for more control on air pollution sources at the local, national and European level.
The unusual weather patterns that made this March one of the driest on record also caused prolonged pollution problems. Frequent easterly winds brought air across some of the most industrial and urbanised areas of northern Europe before circulating it over the UK, northern France and the Low Countries. Gaseous pollution from European and UK agriculture, transport, homes and industry reacted to form airborne particulates.
These mainly affected south-east England, but occasionally spread into the rest of the UK. The greatest concentrations were measured around the last weekend of March in London, where they reached their highest levels for four years (excluding Bonfire Nights).
The same concentrations also affected Plymouth and Port Talbot. The regional air pollution during March caused difficulties for management in cities because it left less capacity for local traffic emissions before pollution limits are breached. The combination of regional air pollution and local traffic meant that air pollution at Marylebone Road in London breached national objectives for 15 days in March, the worst since 2004.
The effects can be seen in health statistics. A recent report by the committee on the medical effects of air pollution estimates that long-term exposure to particulate air pollution shortens the lives of UK residents by six months on average, which was equivalent to around 29,000 deaths in 2008.
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