Air Quality Report

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Air quality in the London Borough of Barnet: A report on the review and assessment process of air quality in the borough.

Placement report submitted as part requirement for the Degree of BSc in Environmental Studies, University of Hertfordshire

In 1995, the Government enacted Part IV of its Environment Act. This act required all local authorities to survey and assess air quality in its area, in relation to set objectives established by the NAQS. The authorities were required to undertake at least the first stage of a three stage review process, and, should it prove that levels of one or more pollutants would exceed the NAQS objectives, develop a strategy for meeting the objective by the specified time limit. The authorities were also required, if necessary, to designate AQMAs in their areas.

Barnet is one of the boroughs of London, with a population of more than 300,000. It possesses a number of pollution sources, such as industrial works and the borough's road and rail networks. Barnet council began its review of the borough's air quality in 1997, and continued the process constantly until its completion in 2001.

The first stage review consisted of screening possible sources of pollution in the borough, identifying the pollutants, and identifying possible causes for further study and assessment. The process screened data from industrial and transport sources, as well as data from the LAQN and DETR. The review concluded that five of the pollutants would require further analysis.

The second stage review was conducted in an abbreviated form, as it was felt that some of the remaining pollutants would necessarily have to be studied at the highly detailed third stage of review. It consisted of modelling potential areas that could be affected by pollutants, as well as modelling each pollutant individually, in order to decide whether any of them would require further study. The second stage review concluded that a third stage review would be necessary for PM10 and NO2, but that the other three modelled pollutants would need no further analysis.

The third stage review concluded that, of the seven pollutants initially studied, two pollutants will exceed the NAQS objectives set for 2004/5. The two pollutants, PM10 and NO2, are generated mostly by motor vehicles, though other sources can be found in the borough. The council began to investigate possible strategies to reduce the levels of emissions generated in the borough. These strategies included pedestrianising areas of the borough, increasing public awareness of alternative modes of transport, and imposing stricter parking penalties throughout the borough.

Barnet council is presently further investigating ways of lowering the levels of PM10 and NO2 in the borough, while consulting interested parties on those strategies developed during the course of the review and assessment process. It has proposed that the entire borough become an AQMA, an action it is felt will improve the borough environment as a whole, rather than just in areas worst affected by pollution.

In response to Part IV of the Environment Act, 1995, it was decided to conduct a survey of the London Borough of Barnet's air quality, and determine which, if any, airborne pollutants required action. The council's Corporate Plan states that the council will take measures to improve the quality of life, (including air quality) for the borough.

Barnet has a number of sources of air pollution. "Road transport, rail transport from diesel trains and prescribed industry… such as crematoria (and) vehicle resprayers." (LBB, 1998) Identification of pollutant sources, and the extent to which these sources contributed to the pollution was one of the early tasks of the survey team.

This project will look at the surveys carried out, and their findings. It is not possible to gauge the success of the work. The aims set out by the project call for deadlines in 2005, some four years distant at the time of writing. What it is possible to assess is the means by which Barnet have surveyed the borough's air quality, and the potential affects this study can have, both at a local scale, and on a wider scale.

This project will also consider the causes of air pollution. The survey suggests that pollution sources can be described generally as line, point, and area sources. This project will locate the sources of pollution in the borough, and attempt to suggest ways in which the levels of pollution can be lowered.

This project will also look at the pollutants that the survey is concerned with. Many pollutants have several sources, and this will be investigated. The effects of the pollutants will also be investigated, as will the means suggested by the investigation for dealing with the pollutants.

The project will also investigate the survey being carried out in the neighbouring borough of Enfield, as a comparison to the work performed by the Barnet review team.

Barnet is one of the thirty-three boroughs of London. It has a population of approximately 320,000 people. It is one of the largest of the boroughs, and is situated to the north of the City of London. Each borough has an administrative council, which has responsibilities for, among other things, maintaining a reasonable local air quality. The borough has several major transport links, with several 'A' roads, crossing the borough, as well as the beginning of the M1 motorway. The M25 motorway is situated to the north of the borough. There are several rail links in the borough, as well as an overground section of the London Underground subway system.

While not heavily industrialised, Barnet does have some sources of industry, mainly light industrial businesses, situated in industrial parks.

The largest open space in the borough is the conservation area of Totteridge Common and its surrounds. The area is characterised by open spaces with little development. Most of the area consists of open grassland, and some wooded area.

This project is to be conducted based on literature review and on personal communications with members of the team tasked with surveying Barnet's air quality. Personal knowledge of the London Borough of Barnet will also be employed, particularly in assessing areas of the borough in which levels of air quality might be expected to be addressed.

The literature consists of Government material, local authority research, and research conducted by private institutions. The literature will be taken from published sources, and Internet sites.

The implications of the study are potentially national in scope. They can form part of the whole: A study of the national air quality, and the means by which the problems may be deal with.

The results will also be of interest to the GLA. The GLA is currently pursuing a campaign of increased public transport use. By utilising the data produced by Barnet and the other London boroughs, they can more effectively put across their case.

On a local level, the results are available to the healthcare authorities. The data can aid health officials in planning for the care of those affected by air pollution. The data can be used to model the likely effects of air pollution. The health authorities can then plan for potential future health issues, e.g. an increase in asthma.

In 1997, the London Borough of Barnet undertook a revision of the air quality of the borough. The first stage of this three-stage review was undertaken in partnership with Middlesex University.

The decision to undertake the review came about as a result of the Government’s commitment to improving national air quality. The Environment Act of 1995 introduced new requirements for air quality management throughout the country, at local and national levels. Further to the Act, the Government issued each local authority with a set of guidelines for the review and assessment of air quality.

In 1997, Barnet Council, in conjunction -initially- with Middlesex University began their review of local air quality. It had been decided that the review would survey the borough for pollutants that "have a significant impact with the authority's borders." (LBB, 1998) These pollutants were decided to be benzene, 1,3-butadiene, carbon monoxide, lead, nitrogen dioxide, fine particles (specifically PM10), and sulphur dioxide. These pollutants were selected after "an initial screening of industrial, transport and other sources of pollutants" (LBB, 1998) within the borough boundaries.

It was acknowledged that air pollution could be caused by sources both inside and outside of the borough, but the study was only focussed inside of the borough. It is difficult to measure how much pollution is caused by external sources and, therefore, it is assumed for the purposes of the survey that all pollution recorded in the borough was caused by sources in the borough. Barnet's position on the edge of London suggests that more pollution leaves the borough for other locations than come in from external sources.

1,3-butadiene (C4H6) is suspected to be a carcinogen. Prolonged exposure to 1,3-butadiene is believed to possibly lead to heart and lung damage, though is this not currently proven. It is known that prolonged exposure to this pollutant can lead to damage to the central nervous system, blurred vision, nausea, fatigue, headaches, decreased blood pressure and pulse rate, and unconsciousness. It is not thought that exposure to benzene has directly resulted in death, but it is possible that this could be an effect of prolonged over exposure. This pollutant can also be a minor irritant, with short-term exposure leading to irritable eyes, nose and throat.

1,3-butadiene can be encountered in a number of environments. It is present in petrol, but is more commonly found in pollution generated by plastic manufacture. It is also found in cigarette smoke, and could theoretically be encountered by "ingesting foods contained in plastic or rubber food containers, but levels are generally very low or not present at all." (ATDSR, 2001)

Benzene (C6H6) is a carcinogen. Prolonged exposure "from less than 5years to more than 30 years" (OSHA, 2001) can lead to the development of cancer in those exposed. In the short term, benzene can cause drowsiness and dizziness, and in extreme cases unconsciousness and death. As well as being possible to inhale benzene, it can be absorbed through the skin.

Benzene is produced by the burning of natural fuels, and can be found in petrol and coal. It is also used in the manufacture of plastics, detergents, pesticides and other chemicals. Recommended maximum exposure to benzene is 1 part per million (ppm) in air for an 8 hour average. Short term exposure to benzene should be limited to 5 ppm.

Carbon monoxide (CO) is an antioxidant, limiting the body's ability to transfer oxygen through the blood stream. Short-term exposure to high levels of carbon monoxide can lead to dizziness, headaches and nausea. In the long term, exposure to high levels of CO can lead to unconsciousness, brain damage, and even death. The recommended exposure level for CO is an eight hour average of 35ppm.

It is reported that "approximately 200 people per year are killed by accidental CO poisoning with an additional 5000 people injured" in the United States. (Twin Cities, 2001) The main sources of CO are automobiles, heating equipment, and gardening equipment. Over exposure to CO can often occur in areas with poor ventilation. Young people are often affected through living in poorly maintained flats with decrepit heating and inadequate ventilation.

Lead can cause poisoning of many of the body's organs. While children are more at risk than adults, over exposure to, and consequent absorption of lead can lead to damage to the circulatory system, brain, kidneys, nervous system and reproductive system. "Symptoms of lead exposure include colic, shock, sever anemia, kidney damage, and irreversible brain damage." (PCA, 2001) Death can also be caused by prolonged over exposure.

Until around 15 years ago, the primary source of lead was petrol. Unleaded petrol has removed the need for lead in petrol, and now sources of lead include smelting, battery plants. Some vehicles still run on leaded petrol, especially classic cars to which catalytic converters cannot be readily fitted. However, the levels of lead in the air have fallen drastically. From a 1970 level of 219,000 short tons, US levels of lead fell to 5,000 short tons in 1994. An acceptable level of exposure to lead has been established as 0.5¼g/m³.

Nitrogen dioxide (NO2) can lead to respiratory difficulties in children. The best known of these difficulties is asthma. It is an irritant, and has been proven to lower the resistance to influenza of those who are exposed. For children, prolonged intense exposure, such as that found near major roads, has been linked to ongoing respiratory trouble, such as asthma.

Nitrogen dioxide sources include motor vehicles, electric utilities and industrial boilers. The Environmental Protection Agency has established that the "health-based national air quality standard for NO2 is 0.053 ppm" as an annual mean. (EPA website, 2001)

Ozone is included as a pollutant in the NAQS objectives. However, ozone has been permitted to be left out of the review and assessment process.

PM10, or particulate matter smaller than 10 microns in size, "may well be killing 10,000 British people prematurely every year." (Birmingham University, 2001) The risk is greatest to those with existing respiratory problems, which are acerbated by the ultra-fine particles in the lungs.

Sources of PM10 include motor vehicles, especially those, such as buses, which are powered by diesel engines. An acceptable exposure level to PM10 has been established as 50 µg per cubic metre.

Sulphur Dioxide is a colourless, non-flammable gas. It is an irritant, causing a burning sensation to the eyes and throat. "Hourly peak values can be as high as 750 ppb on infrequent occasions." (MMU, 2001)

Sources of SO2 include fossil fuel combustion, smelting, the manufacturing of sulphuric acid and the incineration of waste. Acceptable exposure levels are around 100 ppb.

With these pollutants selected, Barnet was required to undertake first stage assessment of the pollutants. The first stage (of three assessment stages) "consists of an initial screening on industrial, transport and other sources of pollutants." (LBB, 1998) Its purpose is to "review current air quality across the Council's geographical area." (SEIPH, 1998) The stage one process must only report on "existing or proposed significant sources of pollution." (SEIPH, 1998)

This first stage, which was compulsory for all local authorities, was carried out in partnership with Middlesex University and SEIPH. SEIPH assisted many other local authorities in the South East of England with their review of air quality. One of these authorities was Barnet's neighbouring borough, the London Borough of Enfield. Enfield's geographical proximity to Barnet makes it ideal for use as a comparative case study for the work carried out by Barnet. The London Borough of Lewisham will also be used for comparison, as it is much nearer Central London, as well as being to the South of the River Thames.

The aim of the review is to decide whether air quality levels within an authority's boundaries will reach the proscribed levels in 2005 as laid down by the Government's National Air Quality Strategy (NAQS). Until this date is reached, the review and assessment continues to be an ongoing process.

Barnet's first stage review was carried out between 1997 and 1998. The council's Environmental Health department was the main Council authority in the project. Stage one of the review and assessment process requires the authority to "compile and collate information on any existing or proposed significant sources of pollution." (LBB, 1998)

The London Borough of Barnet, at the time of this review, is not a particularly industrial area. As with many parts of Southern England, it is mainly commercial and residential in character. Industrial sources of pollution, then, are rare. What examples do exist, such as car resprayers, and the crematoria in the borough, produce relatively small quantities of pollution compared to the heavy industry present as recently as two decades before.

The main sources of data and information examined are as follows: Industrial - LBB public register of authorised processes and the LRC's London emission inventory database. Transport - The LTS database. Other sources - Monitoring data from the LAQN and the DETR website. Data was also gathered from the SEIPH "Air Pollution Toolkit for London," (SEIPH, 1998) a resource which features emissions details from the London Emissions Inventory.

The most productive source of air pollution in Barnet at the time of the review was the borough's road network. Having collected data from the proposed and existing sites of pollution, it became possible to draw the following conclusions:

"For the following pollutants, no further action need be taken: Benzene, 1,3-butadiene." (LBB, 1998)

It was recommended that the remaining five pollutants be subjected to further review. Benzene and 1,3-butadiene had already reached 2005 levels for these pollutants, and there are no signs of the levels rising beyond the NAQS objectives by 2005.

For benzene, the reasons for their exclusion from future study are that the introduction of catalytic converters has lowered the levels of benzene in the air. NAQS levels for 2005 allow for 5% by volume benzene presence in petrol (leaded and unleaded). The use of catalytic converters means that this level, by 1998, had already dropped to less than 2%. The NAQS standard for benzene requires an annual average not exceeding 5 ppb.

Petrol filling stations are a major source of benzene. All new stations are to be fitted with vapour control devices to prevent the release of pollutant vapours being released into the atmosphere. Existing stations are to be fitted with these devices by 2004, thus fulfilling the NAQS 2005 deadline.

It was concluded that the possibility of benzene levels exceeding permitted levels by 2005 was "negligible" (LBB, 1998) and that no further action was required.

For 1,3-butadiene the reasons for its exclusion from further study are that only major industrial sites produce enough of his pollutant to exceed the NAQS standard. Even the busiest roadside is expected to be below the standard by 2005, if it is not already so. The LBB lacks heavy industry in sufficient amounts to exceed the NAQS standard of 1 ppb as an annual mean concentration. In fact, only one site in the UK exceeded this level.

One of the major reasons for the low levels of 1,3-butadiene was, again, the introduction of catalytic converters. Compulsory on all cars built after the 1^st January, 1993, catalytic converters can reduce emissions of 1,3-butadiene by up to 95%. As mentioned above, the control of vapour loss from petrol filling stations will also lead to a lowering of the levels of this pollutant in the air.

It was concluded that the chances of levels of 1,3-butadiene exceeding NAQS standard by 2005 were "negligible" (LBB, 1998) and that no further action was required.

In Enfield, the first stage of the review concluded, "for benzene (and) 1,3- butadiene, Enfield will not have a problem to meet the target objectives." (LBE website, 2001) This result is unsurprising, given the similarities and closeness of the two boroughs.

In Lewisham, the first stage concluded that lead, benzene and 1,3-butadiene met "the current and proposed objectives in Lewisham" (LBL, 2000) and so would require no further analysis. However, Carbon Monoxide, PM10, NO2, and SO2 were deemed to require further study.

Following the review at stage one, the data and conclusions were made public. With the conclusion that it was no longer necessary to investigate benzene and 1,3-butadiene, Barnet Council and SEIPH progressed to the next stage of the review and assessment process. Theoretically, this should have been stage two. However, it had become clear that a stage three review would certainly be necessary, and, therefore, the stage two review could be largely bypassed. While there would still be a stage two review, it would be almost entirely restricted to modelling of the pollutants to decide which of them would be studied in detail at stage three.

Modelling of potential air quality is necessary at stage two. It was required that predictions of local air quality were made up to 2005, by which time the NAQS standards would have to be reached. Modelling allowed for potential areas of high emission to be identified, and the effects of air pollution would have over the time period modelled.

Modelling can be done via utilisation of past pollution data, or via dispersion modelling techniques. The latter is useful for any area in which a pollutant is not modelled, in that it predicts how pollutants can spread out over the borough from sources into areas where a pollutant is not generated.

Continuous monitoring of the borough's air quality becomes necessary at stage two of the review process. However, "the identification of a monitoring site is a complex and involved operation, and is determined largely by the objectives of the authority." (LBB, 1999) What the borough wanted to monitor would influence where the monitoring sites were.

It was decided that "traffic related pollutants are of prime concern." (LBB, 1999) As so many of the pollutants being studied are traffic related -NO2, PM10, and CO- it is correct for more monitoring stations to be established to monitor them. The remaining pollutants, lead and SO2, can be monitored using fewer monitoring stations, as they are not produced as regularly throughout the borough. Monitoring sites in residential areas would be of particular use, as they would show the level of exposure for the local population.

The first stage review was completed in 1998. The remaining pollutants to be studied were Sulphur Dioxide, Lead, Nitrogen Dioxide, particulate matter and Carbon Monoxide. It had become clear that a stage three review would be necessary, and, therefore "a full Stage 2 review and assessment (was) unnecessary." (LBB website, 2001) At this stage of the review, it became necessary to develop models, predicting future patterns in pollution generation and dispersion. It was decided to undertake the modelling of each of the pollutants, which would reveal which of the pollutants would need to be studied in the greater detail of the third stage review process.

Modelling future atmospheric concentrations of pollutants requires that several variables be taken into account. It is assumed that meteorological conditions will conform to a specified average, but that emission rates will alter. For example, the DETR predicted a fall in some of the pollutants generated by motor vehicles, although the increasing number of cars on the roads would somewhat offset this reduction. Modelling studies were required to be carried out until 2005.

The data from local monitoring of air quality was used for the models. The use of this data allowed for extrapolation of conditions in non-monitored areas in the borough. Where circumstances were similar in non-monitored areas to those found at sites where monitoring took place, e.g. similar traffic patterns or industries, the data was used as an indication of levels at the non-monitored site. Improvements in emission reduction technology were also taken into account for the creation of models.

Other factors were taken into account in the construction of the models. These included: Areas with high emission rates of known pollutants; Areas along main roads with high traffic rates; Areas where a congregation of high buildings could augment pollution build up; Sites where the surrounding areas would be particularly susceptible to high levels of pollution e.g. schools or care homes.

Using these, and other, criteria, a number of sites were chosen throughout the borough for stage two analysis. Combining these factors with knowledge of the local area, five 1x1 km sites were chosen for initial analysis. These sites were:

Brent Cross, A406 junctions with A5, M1 and A41, also Brent Cross shopping centre.

At stage two, models need not be particularly complex. The models are only a guide, showing probable developments and trends over a short period of time. Potential sources of pollutants included line sources, point sources and area sources.

For point sources, the calculations were carried out using data taken from the LAEI emissions database, as well as assumptions about the pollution generated by each of the modelled industrial processes. Several other factors had to be included in the modelling process. These included the types of pollutant generated, how much of the pollutant was being generated (measured in kilograms per second), and how long the generation of the pollutant would last. The stipulated weather for the modelling was classed as "a very stable meteorological condition" (LBB, 1999) with a wind speed of 1 m/s. Background levels of pollution were also taken into account, in order that only the pollution from the source was measured.

The point source models were programmed to produce several results. The models were required to produce data for the location of the worst concentration of pollutants from a source, as well as how great a concentration of pollutants would be present at that place.

The pollutants were predicted over the time periods set by the NAQS air quality standards. (Table 1) For the most part, point sources were expected to conform to the air quality standards, although in the immediate vicinity of Brent Smelt Works, "an exceedance of the SO2 was predicted under this specific meteorological condition to occur 3.63m from this stack." (LBB, 1999). In other cases, slight exceedances were sometimes projected, but always in the immediate vicinity of the source, and always in industrial areas that would be less sensitive to the exceedance.

The most common source of projected exceedance of the standards were the borough's vehicle respraying sites, cement works and the concrete crushing plant. All showed exceedances of the PM10 standards. For the concrete and cement plants, the exceedances were at a very close proximity, and as they are located exclusively in industrial areas, the problem is of only minor concern. The vehicle respraying sites, of which there are approximately five in the borough, could, however, be a significant contributor to high PM10 levels in their local area.

The contribution of road sources to air pollution was also modelled at stage two. It had been theorised at stage one of the review of the borough's air quality that pollution caused by road vehicles was the biggest source of many of the modelled pollutants. The modelling of road pollution sources, therefore, would be a vital part of the investigation into the borough's air quality.

Data was collected from each of the five roads (Appendix one) and then the data was modelled for future pollutant concentrations. The pollutants were modelled over their relevant averaging times, for ease of comparison to the NAQS standards. The model took into account several factors such as projected climate conditions, vehicle velocity, projected traffic flow and background pollution levels. The pollutants modelled were NO2, CO, Benzene and PM10.

Traffic modelling allowed many more areas than the initial five to be modelled. The five initial roads were chosen as representative studies, from which could be extrapolated data that would be valid for a number of roads in the borough. This provided estimates for exceedance levels throughout the borough.

Modelling of traffic sources throughout the borough stage suggests that, even with the ongoing increase in the number of vehicles (1.7% a year - LBB, 1999) the 2005 pollution levels will not usually exceed the NAQS standards. There are some exceptions to this statement, however. The NO2 standard, for example, was predicted to be exceeded on several roads in the borough, particularly near busy roads, where a canyon effect is caused by nearby building of several stories in height.

For Carbon Monoxide, the model predicted that the standards would not be exceeded on any of the borough's roads. However, it was thought possible that the M1 and A406, the two largest roads in the borough, would have CO levels approaching the NAQS standards. The standards allow for roads that are heavily used, as the M1 and A406 are, to exceed the permitted levels by a small amount.

For Benzene, the predicted levels of vehicle caused pollution were not thought likely to exceed the proposed standard anywhere in the borough. For PM10 the standard was predicted to be exceeded throughout the borough.

While roads throughout the borough were modelled for pollution levels, railways were not. Therefore, "a recommendation is made to investigate potential air quality levels... in the areas close to main railway lines." (LBB, 1999) This would establish how much pollution is generated by the railway systems in the borough. As there are both London Underground and British Rail services in the borough, then this could be a significant source of pollution.

With the results produced by the models, the borough's stage two modelling of air quality was complete. The modelling had suggested that only Nitrogen Dioxide and PM10 were of sufficient interest to warrant further study. It was concluded that these two pollutants were "a particular health related" (LBB, 1999) concern, and that further detailed analysis at stage three of the review process was necessary. For the other pollutants, it was decided that the models suggested there was little likelihood of the levels of pollutants exceeding the NAQS standards.

Drawing from the results generated by the models, a number of schemes for combating rising levels of air pollution were suggested. Such initiatives as Park-and-Ride schemes and the pedestrianisation of parts of the borough which experience particularly heavy traffic flow were mooted. It was decided that these possibilities should be investigated while the third stage review was being conducted.

At stage two of the Enfield review, it was concluded that the target levels for Carbon Monoxide and Lead would be met. The stage two review further concluded, however, that further analysis of PM10, Sulphur Dioxide and Nitrogen Dioxide would be necessary. The borough decided to move to stage three analysis of these pollutants.

At stage two of the Lewisham review, it was concluded that Carbon Monoxide levels in the borough would meet objectives, but that NO2, PM10, and SO2 levels would require analysis at stage two.

At stage three of the review and assessment process, "local authorities are required to undertake an accurate and detailed review and assessment of current and future air quality." (LBB, 1, 2000) The council must study air quality both in Barnet, and throughout the rest of London. However, local councils need only use the results for other boroughs as a comparison for their own. The conclusions drawn at this stage will decide the need for further action, for example the establishment of AQMAs. The data will also be necessary for deciding whether any areas are particularly exposed to a pollutant, and if any action other than establishing an AQMA would be beneficial. At this stage of the review process, Nitrogen Dioxide and PM10 were the pollutants remaining to be investigated.

At the time of this report, the third stage of the review and assessment was not complete. The public consultation draft had recently been made available, however, and the results of the review process were complete and available.

Once again, computer models were constructed to create predictions for future levels of air pollution. The data was modelled from NO2 and PM10 levels from 1996 and 1997. For 1996, PM10 was at its highest concentration, while for NO2 1996 was used as a 'typical' year. In 1997, NO2 was at its highest concentration, while PM10 levels from this year are used as a 'typical' example.

At the time of the review, there were new proposed objective levels for both NO2 and PM10. These levels are shown in Table 2, along with the levels previously set as objectives. It was predicted at the start of the review that "Barnet will exceed the objective of 50¼g/m³ (for PM10)" (LBB, 1, 2000) but that it was "considered very unlikely" (LBB, 1, 2000) that the NO2 levels would be exceeded.

For the third stage of the process, the Council must undertake a detailed, accurate review and assessment of the borough's air quality, both present and future. To determine the current air quality requires monitoring stations, of which three were established in the borough. Two of these stations had fixed locations, in order that constant readings were available. The third station was portable, and was used to take readings throughout the borough. The monitoring was conducted in accordance with guidelines issued by the DETR. The sites for the three station Tally Ho, in North Finchley, Strawberry Vale, and Chalgrove School.

Tally Ho was chosen for the first monitoring station as it was felt it would provide god roadside pollution data. Tally Ho is an area of "known pollution and congestion." (LBB, 2, 2000) Chalgrove School was chosen for its location, being close to, but not on, a main road, and also because, as a school, it is a site of high sensitivity. Strawberry Vale was chosen because it is a residential area, ad also is close to the A406 and Finchley Road.

For PM10, the three monitoring sites were used to collect data. As with NO2, it was discovered that the greatest concentrations of particulate matter would occur along the main roads of the borough, with point sources such as the cement works and crematoria producing high concentrations as well.

Nitrogen Dioxide was found in its highest concentrations near roads, and in central London location. It was found that the greater the distance from central London, the lower the concentrations of the pollutant. Specific to the London Borough of Barnet, it was believed that exceedances would occur along many of the Borough's main roads.

The three main monitoring sites for air quality in the Borough were used to collect data on NO2. However, throughout the borough, there were also nineteen diffusion tubes, which were also used to study NO2 levels. These tubes were partly sponsored by local residents, in an ongoing programme.

For PM10, the predictions suggest that, at the current rate of decrease, the NAQS objective for PM10 will not be met by the end of 2004. Of particular concern, is that "the objective will be exceeded along the main traffic routes in the borough." (LBB, 2, 2000) It is also noted that the background levels of particulate matter, that is, levels more than 50m from a source are sometimes exceeding the NAQS objectives. Notable roads for background exceedances include the A406, the M1 and the A1000, Barnet High Road. Predicted levels of exceedance for the entirety of London, including Barnet, were between 58 and 68¼g/m³, whereas the objective requires levels of 50¼g/m³.

For NO2, the monitoring also suggest that major roads are the biggest source of pollutants. While background levels of NO2 are not expected to exceed the objective, it is thought that the main traffic routes will be the sites of exceedances throughout the borough. Again, it is felt that roads such as the A406, the M1 and the A1000 will be major sources of this pollutant. However, it was predicted that the peak hour NO2 objective, which allows for short term 'spikes' in the level of the pollutant, would not be exceeded in Barnet.

London wide, the results were similar. PM10 levels exceeded the NAQS objective at every point in the city. For Nitrogen Dioxide, all but one of the monitoring stations recorded exceedances of NO2 at the yearly average. For the peak hourly rate, however, only about half of the London sites recorded exceedances of the objective (150ppb) and none of the se exceedances were recorded in Barnet.

The council has acknowledged that, at present, the NAQS objectives will not be met for PM10 and NO2. With this in mind, it is further investigating possibilities for reducing pollution levels in the borough. In the meantime, it had set out a number of strategies which would go towards improving the borough's air quality.

The third stage review for Enfield established that "areas of exceedance are predicted to arise in 2005 for... Nitrogen Dioxide (and) PM10." (LBE, 2000) The report concluded with the suggestions that the Council further assess the potential for exposure at sites identified as exceeding the objectives, that the consultation on the findings with all required consultees, and that the council begin the process of designating one or more AQMAs in the borough.

In Lewisham, as well, the third stage report concluded that PM10 and NO2 levels would exceed the objective levels. The council, as a result of the report, then considered the possibilities for establishing a series of AQMAs in the borough.

"Assess the potential for personal exposure at each of the sites identified as exceeding the NAQS objectives.

Undertake consultation on the findings arising from this report with the statutory and other consultees as required.

Initiate procedures within the Council to designate Air Quality Management Areas, based on the areas of exceedance identified." (LBB, 2, 2000)

It was decided that, as part of the consultation process, opinions would be sought on potential methods of reducing pollutant output. Due to the high percentage of the pollution being generated by automobiles, most of these schemes and techniques would be centred on the borough's road vehicles, whether reducing the pollution generated, or cutting back on their use. Many of the ideas for combating vehicle pollution were developed for the council's ITP for 2001-2002.

One of the ideas was to try and encourage greater use of public transport. It was thought that encouraging development in areas well served by public transport (e.g. near to one of the borough's Underground or rail stations). The council planned to work with transport providers, such as Arriva and MTL, to provide improved service throughout the borough.

The ITP also suggested increased East-West bus routes in the borough, as well as making buses more accessible for those people with disabilities. Low-floored buses, which allow easier access for those in wheelchairs, or who find steps difficult, now serve many routes. It is thought that if the number of bus services can be increased so that all areas of the borough are served, then a much higher number of people will make use of them. The council, through its involvement in the LBPN, is establishing priority lanes on roads with bus routes throughout the borough. London wide, the council is aiming to assist with improved public transport links, in an effort to promote widespread use of buses, trains, and the London Underground.

As is required by the review and assessment process, the council has designated an AQMA. In Barnet, the AQMA will cover the entire borough. This, it is felt, will allow the council to "focus our efforts and resources on the areas worst affected by pollution." (LBB, 2, 2000) It will also give the council "the flexibility to link into and support other borough wide initiatives... and in particular to improve air quality in 'areas of special action'." (LBB, 2, 2000)

The council feels that declaring the entire borough as an AQMA will act as a boost to existing environmental schemes in the borough. It aims to support such schemes, as well as working closely with health and transport organisations.

The council is also keen to promote alternative forms of transport, such as walking and cycling. It recognises the need to improve the current facilities for cyclists, and that for groups, the "environment must be improved" (LBB, 3, 2000). To improve the environment for cyclists, more cycle-only paths must be established in the borough. Punishments must be enforced for the use of these routes by anyone other than cyclists. These routes should be sensibly located, to encourage use by cyclists, as well as to ensure the safety of users. The council publishes a guide identifying cycle routes throughout the borough.

The council's pedestrian strategy is to focus on locations where there are a significant number of pedestrians. The council aims to keep these areas clean and free of excess vehicles, as well as ensuring that the walkways are safe and of good quality. Pedestrianisation of certain areas in the borough has been discussed, but the council recognises that certain areas of the borough which could be pedestrianised, e.g. Tally Ho Corner or Barnet High Street, are also areas which serve as main roads. Pedestrianising such areas would lead to severe traffic problems, unless alternative arrangements could be made for the diverted traffic flow. Nearby Hoddesdon, in Hertfordshire, could serve as an example of how pedestrianisation can be achieved with only minor disruption to traffic flow.

Should pedestrianisation occur, then the council should take note of the example of Laconia, New Hampshire, USA. "Laconia spent $5 million pedestrianising its town centre, to make it a pleasant shopping centre." (Bryson, 1999) The scheme failed to attract shoppers. While the area was beautiful, and received plaudits from urban planners throughout America, shoppers disliked being forced to walk to the shops, and instead chose to drive to out of town shopping centres. With nearby shopping centres at Brent Cross (which is inside the borough) as well as Lakeside and Bluewater shopping centres, it is not inconceivable to envisage an abandoned Barnet High Street. Before any firm moves can be made on this idea, consultation would have to take place with local residents, as well as local shop owners.

Parking is an extremely important issue in dealing with pollution caused by vehicles. On-street parking can cause restricted traffic flow, leading to traffic jams and an increased local level of pollution. However, on-street parking is necessary, as there are not enough off-road parking spaces available in the borough, especially with the increasing number of two- or three-car families. The problem of on-street parking is at its most prevalent in residential areas, where many roads lack any facilities for off-street parking. However, main roads in the borough can easily become congested as well, especially during the early mornings when shops are receiving deliveries, and commuters are attempting to make their way to work.

The current policy encourages short term parking in the town centres. This is achieved through parking controls, such as clamping or towing, as well as off-street car parks whose charges encourage short-term stays, to increase the number of people who can make use of the facilities. The council is working to improve many car parks near the town centres, to make them more attractive to potential users. It is acknowledged that the local economy is reliant on cars, and that to rashly introduce schemes to limit people's ability to use their cars would be a mistake. However, the council's long term goal is to cut back on the number of cars on the borough's roads, and recognises parking strategies as one means of accomplishing this.

In fact, the council has set specific targets for the reduction of vehicle usage in the borough:

To reduce vehicle usage in the borough, the council has adopted many schemes. These include raising public awareness, green travel plans, and ensuring safer routes around the borough's schools. The possibility of a walking bus scheme, where parents and/or teachers collect pupils from a number of homes on their way into school, was discussed, but will not be put into practise as of yet.

It should be noted that the GLA, in consultation with LPAC, has established "area wide road traffic reduction targets" (LPAC, 2000) for the whole of Greater London. Barnet, on the outskirts of London, was set a minimum reduction of automobile traffic of 10% by the end of 2010.

Necessarily, the drive to improve air quality in the London borough of Barnet will be a long-term process. Road vehicles are by far the biggest source of pollution in the borough, and reducing their numbers, or even just the number in use at any one time, will take patience. Around sixty percent of journeys undertaken in Britain involve use of a motor vehicle, a figure that will have to be reduced markedly for the NAQS objectives to be met.

It is the boroughs motor vehicles that must be focussed on. Point sources of pollution must already conform to government standards for pollution control. While vehicles too must conform to the guidelines, there are many thousands of vehicles in Barnet. The council has adopted a number of strategies for combating the effects of vehicles on the borough's roads.

Possibly the most important of these strategies is the council's focus on public transport. The council must work with the transport companies to improve service frequency, service availability, and raise awareness of the range of public transport option in the borough. Bus routes would also benefit from assigned lanes in especially busy areas, such as Barnet High Road and Whetstone High Road, but this is something that is necessarily limited by available space.

The further study of air quality in the borough is continuing, and will involve co-operation between local authorities throughout the country. That the NAQS objectives were set as targets for the entire country shows that improving air quality is not just a local concern. Air pollution in Barnet could be caused by a source in the next borough, the other side of London, or even further afield. Each local authority must play their part in countering air pollution, in the knowledge that air quality is not just a local issue.

Pollutant	Standard concentration	Standard measured as	Objective to be achieved by end of 2005
Benzene	5ppb	Running annual mean	The air quality standard
1,3-butadiene	1ppb	Running annual mean	The air quality standard
Carbon Monoxide	10ppm	Running 8-hr mean	The air quality standard
Lead	0.5¼g/m³	Annual mean	The air quality standard
Nitrogen Dioxide	150ppb 21ppb	1-hour mean Annual mean	The air quality standard
Ozone	50ppb	Running 8-hr mean	50ppb measured as the 97^th percentile
Fine Particles (PM10)	50¼g/m³	Running 24-hr mean	50¼g/m³ measured as the 99^th percentile
Sulphur Dioxide	100ppb	15 minute mean	100ppb measured as the 99.9^th percentile

Pollutant	Existing NAQS objective (by end 2005)	Proposed NAQS objective
PM10	50¼g/m³ as 99^th percentile of 24 hour running mean	50¼g/m³ as 24 hour mean not to be exceeded more than 35 times per annum (By end 2004)
NO2	21 ppb annual mean, 150 ppb averaged over one hour	21 ppb annual mean, 105 ppb averaged over one hour, not to be exceeded for than 18 times per annum (By end 2005)