Short Report on Air Quality in Bristol
Steve Crawshaw
September 2019
Introduction
This report is intended as a concise summary of the most recent air quality measurements, policies and plans in Bristol. The report summarises the key air quality monitoring data from 2018. The full, detailed information is contained within the 2019 annual report. More information, including live air quality data and historic reports on air quality is available on our website.
Air Quality Monitoring
Monitoring in Bristol focusses mainly on oxides of nitrogen and specifically NO2 (nitrogen dioxide) as this is the regulated pollutant which is at high enough levels to cause concern. Annual mean concentrations exceed government and EU limits. Bristol has an extensive network of monitoring sites, using both passive (diffusion tubes) and continuous instruments. PM10 is monitored at two sites in Bristol by the government at AURN (Automated Urban and Rural Monitoring) sites. These are located in St. Pauls and on Temple Way. Summary data from these sites is presented in this report. All of our data is available online through the air quality dashboard.
The map shown below illustrates the locations of air quality monitors and pollutants measured at currently operating sites in 2018.Fig. 1: Map of current monitoring sites
Nitrogen Dioxide
Continuous Instruments
We monitor oxides of nitrogen, including the regulated pollutant nitrogen dioxide (NO2) at seven sites. This includes AURN and affiliated sites. our stations are mainly located at the roadside to capture “worst case” ambient conditions. A typical monitoring station is shown below.
Continuous monitoring site
Nitrogen dioxide is primarily a traffic pollutant in urban areas and tends to be measured at higher levels in winter because of poorer dispersion and higher emissions. Concentrations fall off rapidly as you move away from the roadside. Fig. 2 shows the summary plot of nitrogen dioxide at BCC and AURN sites.
Fig. 2: Summary plot of NO2 at continuous sites
Trends in NO2
Concentrations of NO2 have not fallen as fast as anticipated due to failings in the test regime for new vehicles (EURO standards) and manipulation of test results by some diesel engine manufacturers. Fig. 3 below shows the smoothed trend of NO2 at continuous sites.
Fig. 3: Smoothed trend of NO2 at Continuous sites
Time variation of NOx
Oxides of nitrogen (NOx) are emitted from vehicle exhausts and the nitric oxide (NO) is oxidised in air to form NO2. The plot below shows how NOx varies over time. It can be seen that there is a clear association between morning and evening “rush hour” traffic. Pollution also increases in winter and is reduced at weekends when traffic is lighter.
Fig. 4: Time variation of NOx at BCC sites
Diffusion Tubes
Diffusion tubes are small passive devices that absorb NO2 at a known rate. 
They can be cheaply and widely deployed to give a good indication of the spatial variation in nitrogen dioxide. The table below summarises bias adjusted annual mean concentrations of NO2 at a long - running subset of roadside diffusion tubes.
Table 1: Summary data from some roadside diffusion tubes
Trends of NO2 at city centre diffusion tubes
The plot below shows the trends in NO2 at a subset of city centre diffusion tube sites. There is considerable variation in the trend between the different sites.
Fig. 5: Trend of NO2 at selected city centre diffusion tube sites
Locations and concentration at current diffusion tube sites
The map shown below indicates the concentrations at the 127 diffusion tubes operating in 2018.
Fig. 6: Thematic map of NO2 at diffusion tube sites
Particulate Matter (PM10 and PM2.5)
Particulate Matter or PM is fine particles that can enter the lungs and cause health problems over the long term. Some is emitted from exhausts, tyre and brake wear, but there is also a significant component emitted from solid fuel burning and even natural sources. PM10 is measured at the two AURN sites in Bristol. The plots below show summary data for PM10. A PM10 site was recently added to Bristol City Council’s network at Colston Avenue.
Fig. 7: Time Series Plot of Particulate Matter at Bristol sites
Summary Statistics
Statistics for current year
| site | pollutant | dat.cap | mean | max | max_daily | percentile.99.8 | percentile.90.4 | hours |
|---|---|---|---|---|---|---|---|---|
| AURN St Pauls | NO2 | 83.9 | 23.8 | 115.9 | 51.9 | 92.5 | 46.7 | 0 |
| AURN St Pauls | O3 | 83.6 | 50.8 | 162.8 | 106.0 | 145.2 | 82.8 | NA |
| AURN St Pauls | PM10 | 79.7 | 15.9 | 108.9 | 48.0 | 57.4 | 29.8 | NA |
| AURN St Pauls | PM2.5 | 79.9 | 12.0 | 88.6 | 46.1 | 50.9 | 24.1 | NA |
| Brislington Depot | NO2 | 97.3 | 25.4 | 109.8 | 60.6 | 90.2 | 46.0 | 0 |
| Colston Avenue | NO2 | 8.3 | 67.2 | 196.9 | 101.3 | 180.9 | 118.3 | 0 |
| Fishponds Road | NO2 | 95.9 | 41.5 | 220.8 | 120.0 | 143.8 | 70.2 | 1 |
| Parson Street School | NO2 | 99.7 | 39.0 | 143.8 | 70.0 | 112.0 | 67.0 | 0 |
| St. Werburghs | NO2 | 5.5 | 22.6 | 250.5 | 44.0 | 69.2 | 41.8 | 1 |
| St. Werburghs | O3 | 5.5 | 16.5 | 438.0 | 89.7 | 110.8 | 40.4 | NA |
| St. Werburghs | PM10 | 5.5 | 10.4 | 182.2 | 24.3 | 71.7 | 19.0 | NA |
| St. Werburghs | PM2.5 | 5.5 | 2.7 | 30.0 | 12.2 | 29.8 | 6.4 | NA |
| Temple Way | NO2 | 98.1 | 44.3 | 180.5 | 84.7 | 129.4 | 81.1 | 0 |
| Temple Way | PM10 | 94.1 | 22.6 | 117.9 | 54.5 | 81.7 | 39.6 | NA |
| Wells Road | NO2 | 97.9 | 33.0 | 168.8 | 81.8 | 118.3 | 59.2 | 0 |
Historic Statistics
The table below can be filtered on each field.
Table 3. Historic Continuous air quality summary statistics