Air quality

Review and Assessment of Nitrogen Dioxide

Information about air quality in solihull

7 Review and Assessment of Nitrogen Dioxide

7.1 The Government

has adopted two air quality standards for nitrogen dioxide (NO₂):

A 1-hour mean of 200 µg/m³ (105 ppb), with the objective that it may be exceeded no more than 18 times per year by the end of 2005 (approximately equivalent to the 99.8^th percentile of the total annual hourly values).

An annual mean of 40 µg/m³ (21 ppb), with an objective of meeting that standard by the end of 2005.

For the 1-hour objective, the focus of the review and assessment should be on any non-occupational exposure at near ground level outdoor locations, including roadside sites.

For the annual mean objective, the focus of the review and assessment should be on non-occupational exposures at near ground level outdoor locations, including:-

• Background locations,
• Roadside locations, such as on pavements or close to the facades of buildings,
• Other locations where people may be exposed regularly, such as in the vicinity of housing, schools or hospitals.

7.2 Nitrogen dioxide

is a gas formed by the reaction of nitrogen and oxygen in combustion processes. The reaction usually takes place in two stages, the first resulting in the combination of one atom each of nitrogen and oxygen to form nitric oxide, this compound being oxidised over time to produce nitrogen dioxide. Wherever nitrogen dioxide occurs, nitric oxide is also found, and these compounds are collectively known as total oxides of nitrogen (NOx).

7.3 Although there are a number of natural sources of oxides of nitrogen

including forest fires and lightning, most of the nitrogen dioxide found in the atmosphere, near ground level in the United Kingdom, is likely to have resulted from human activity.

7.4 The main sources of nitrogen dioxide

for non-occupational exposures are emissions arising from the combustion of fossil fuels in road transport, power stations and other industrial and commercial activities.

7.5 Specific sources of nitrogen dioxide in Solihull are:

• Emissions from motor vehicles,
• Emissions from industrial combustion plant,
• Emissions from commercial combustion plant,
• Emissions from space heating equipment in homes, hospitals and schools.

Sources of Total Oxides of Nitrogen in the West Midlands

Figure 7.1

7.6 Nitrogen Dioxide Levels in 1999

Air pollution is measured at a number of locations across the West Midlands conurbation. Some of the monitoring stations are owned and operated by the Government, as part of the Automatic Urban and Rural Network (AURN). Others are owned by Local authorities, but are affiliated to the AURN. Also included is a monitoring station at Birmingham Airport. In this report, the levels of nitrogen dioxide, measured at AURN stations in neighbouring authorities, are included to demonstrate the relationship between the levels, across the conurbation.

18 Highest Hourly Values in the West Midlands Nitrogen Dioxide, 1999

Figure 7.2 shows that the first of the Air Quality Standards 2000 for nitrogen dioxide; 200 µg/m³, expressed as the 18^th highest hourly concentration, was met at all the AURN monitoring stations, in 1999.

Annual Average Values in the West Midlands Nitrogen Dioxide, 1999

Figure 7.3 shows that the other Air Quality Standard 2000 for nitrogen dioxide; 40 µg/m³, expressed as the annual average concentration, was exceeded at only one monitoring station; Walsall Alumwell.

Solihull MBC has a mobile air quality station that has been in operation since 27th April 2000. It has been located at two urban background sites: Coppice Junior School (off Damson Lane) from 27th April 2000 to 15th October 2000, and Marston Green Infants' School from 30th October 2000. Figures 7.4 and 7.5 show the monthly averages and the 18th highest hourly mean respectively for nitrogen dioxide as recorded at the station.

N02 Monthly Averages May 2000 - Mar 2001

Figure 7.4

NO2 18th highest hourly Average

Figure 7.5

The trends in the maximum and annual average concentrations of nitrogen dioxide are shown in figures 7.6 and 7.7q, respectively. Both have shown a progressive improvement throughout the 1990s. Although the concentrations of air pollutants vary from year to year, due to varying weather patterns, the overall levels of pollution will drop if the emissions of a pollutant are falling.

Thus, as the vehicle fleet changes, due to the introduction of new vehicles with lower emissions and the removal of older vehicles with higher emissions, less of oxides of nitrogen are emitted and the air quality improves.

Trends in West Midlands Air Quality Nitrogen Dioxide: 18th Highest Hourly Value

Figure 7.6

Trends in West Midlands Air Quality Nitrogen Dioxide: Annual Average Values

Figure 7.7

7.7 Nitrogen Dioxide Levels in 2001

In addition to the AURN data, Solihull MBC commenced a diffusion tube monitoring programme for Nitrogen dioxide levels in the Borough in 2001. This was in response to a consultation response from the Department of the Environment, Food and Rural Affairs (DEFRA) that the only air quality monitoring in Solihull was at the airport, as outlined in paragraph 12.1 of the consultation chapter. Five or six tubes were exposed at each of four roadside sites, representing the Borough's busiest and most congested roads with nearby housing, for a period of four weeks from February 2001 to December 2001. Monitoring sites were also situated at two background locations. The tubes were mounted on lamp posts at the kerbside as opposed to building facade and as such represent the worst case scenario. A summary of the diffusion tube data is given in the table below.

The eleven month averages for each site are well under the annual average NO2 objective for 2005 of 40 µg/m^3. This indicates the air quality in the areas where people are living in close proximity to heavily used roads in Solihull, already meet the 2005 air quality objectives for nitrogen dioxide.

The average Nitrogen Dioxide concentrations for 2001 as measured by diffusion tube

7.8 Projections of Measured Values

The concentrations of nitrogen dioxide, to be experienced in Solihull during the early part of the 21^st century, will be governed by the trend in emissions of total oxides of nitrogen.

The annual emissions of nitrogen oxides are expected to continue to fall, as the proportion of vehicles, with effective emission control systems, increases. The emissions inventory, compiled for the Review and Assessment of Air Quality, indicates that the reduction in the annual emissions of nitrogen oxides from motor vehicles is likely to be around 45%, or 40% from all sources.

Whilst the airborne concentrations of nitrogen dioxide cannot exceed the levels of total oxides of nitrogen, they are not likely to fall in direct proportion, due to a reservoir of nitric oxide, present in the atmosphere, and from which nitrogen dioxide is formed.

Figure 7.8 shows the trend in the values measured at the longest serving AURN station in the midlands, Birmingham Centre, and alongside some of the heavily trafficked roads. The graph indicates the likely change in the maximum hourly concentrations of nitrogen dioxide as the emissions of all oxides of nitrogen fall. It suggests that this air quality objective is unlikely to be breached anywhere within Solihull.

Trends in West Midlands Air Quality Nitrogen Dioxide: 18th Highest Hourly Value

Figure 7.8

Figure 7.9 shows the likely change in the annual average concentrations of nitrogen dioxide under similar conditions, at the same locations. It indicates that, whilst the Air Quality Standard is likely to be met in the general urban environment, it may still be exceeded, in 2005, alongside some highly trafficked roads.

Trends in West Midlands Air Quality Nitrogen Dioxide: Annual Average Values

Figure 7.7

7.9 Projections Based on Emissions Forecasts

The levels of nitrogen dioxide have been calculated using the Airviro gaussian model, for both the present time and for 2005.

The 1998 emissions database was used to calculate the hourly maximum and annual average concentrations for two different sets of meteorological data; 1996 and 1998. The weather in 1996 was characterised by a number of periods of high pressure with low winds and stable conditions, which favour the accumulation of air pollutants, whilst the weather in 1998 was characterised by windier conditions, which favour the dispersion of air pollutants.

The 2005 emissions database was then used to calculate the hourly maximum and annual average concentrations using the 1996 meteorological data, which represents the "worst case" for pollution values.

Pollution maps have been prepared from the modelled data to illustrate the distribution of the maximum and average levels of nitrogen dioxide across the Borough for the present time (1998) and for 2005; the target year for compliance with the nitrogen dioxide objectives.

The colour scheme used for the pollution maps is designed to demonstrate the relationship between the predicted values and the relevant nitrogen dioxide objective. Values near to or above the objective are displayed in orange and red. Values displayed in blue and green represent low or intermediate values so that those areas are highly unlikely to exceed the objective.

Figures 7.11 and 7.13, below, show how the maximum hourly levels of nitrogen dioxide are expected to change over the next five to seven years.

The rural parts of Solihull already experience low levels of nitrogen dioxide and these are expected to fall further by 2005.

Although the levels of nitrogen dioxide, in the urban parts of Solihull are higher, they are still well below the maximum hourly objective for nitrogen dioxide. It is interesting to note that the modelled values pick out the slightly higher values in Solihull town centre and Shirley, and that they show the effects of the conurbation extending out to the M42 motorway.

In the 2005 representation, the levels have fallen in both Solihull town centre and Shirley and the M42 motorway stand out as an isolated source. The model has confirmed the projections from the measured data, which indicated that the maximum hourly levels of nitrogen dioxide should not exceed the objective in 2005.

The annual average nitrogen dioxide levels, in 2005 (Figure 7.12), also show a marked reduction across most of Solihull, as compared with the current values (Figure 7.10).

Solihull is characterised by a low building density, with large gardens and many roadside verges. Thus, despite a degree of traffic congestion, pollution from motor vehicles tends to be diluted quickly beyond the carriageways.

Thus, as the model indicates, the annual average objective for nitrogen dioxide should be met throughout the borough of Solihull.

Distribution of Average Nitrogen Dioxide Levels 1998

Distribution of Maximum Nitrogen Dioxide Levels 1998

Distribution of Average Nitrogen Dioxide Levels 2005

Distribution of Maximum Nitrogen Dioxide Levels 2005