Oxfordshire Summer 2024 Ozone
Elevated ozone in Oxfordshire during Summer 2024
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1 Introduction
1.1 Purpose
This report closely examines ozone (O3) concentrations measured at the Oxford St Ebbes monitoring station in Oxford to assess how Oxfordshire was impacted by elevated ozone throughout summer 2024.
1.2 Data
In 2024, Oxfordshire’s air quality network was comprised of 7 AURN/Air Quality England sites. Figure 1 shows a map of these sites. Links to each of their respective OxonAir site information pages are included in each marker popup. Oxford St Ebbes, the only site which measures ozone, is highlighted in orange.
2 Daily Air Quality Index (DAQI)
2.1 What is the DAQI?
The Daily Air Quality Index (DAQI) tells you about levels of air pollution and provides recommended actions and health advice. The index is numbered 1-10, low (1) to very high (10), and divided into four bands to provide detail about air pollution levels in a simple way, similar to the sun index or pollen index (“Daily Air Quality Index (DAQI)” 2023).
“Daily Air Quality Index (DAQI).” 2023. Oxfordshire County Council. https://www.oxonair.uk/about-air-quality/daily-air-quality-index-daqi.
| Band | DAQI | O3 |
NO2 |
PM2.5 |
PM10 |
|---|---|---|---|---|---|
| Low | 1 | 0 – 33 |
0 – 67 |
0 – 11 |
0 – 16 |
| 2 | 34 – 66 |
68 – 134 |
12 – 23 |
17 – 33 | |
| 3 | 67 – 100 |
135 – 200 |
24 – 35 |
34 – 50 | |
| Moderate | 4 | 101 – 120 |
201 – 267 |
36 – 41 |
51 – 58 |
| 5 | 121 – 140 |
268 – 334 |
42 – 47 |
59 – 66 | |
| 6 | 141 – 160 |
335 – 400 |
48 – 53 |
67 – 75 | |
| High | 7 | 161 – 187 |
401 – 467 |
54 – 58 |
76 – 83 |
| 8 | 188 – 213 |
468 – 534 |
59 – 64 |
84 – 91 | |
| 9 | 214 – 240 |
535 – 600 |
65 – 70 |
92 – 100 | |
| Very High | 10 | 241+ |
601+ |
71+ |
101+ |
| AP Band | Accompanying Health Messages | |
|---|---|---|
| at-risk individuals | the general population | |
| Low (1-3) | Enjoy your usual outdoor activities. | Enjoy your usual outdoor activities. |
| Moderate (4-6) | Adults and children with lung problems, and adults with heart problems, who experience symptoms, should consider reducing strenuous physical activity, particularly outdoors. | Enjoy your usual outdoor activities. |
| High (7-9) | Adults and children with lung problems, and adults with heart problems, should reduce strenuous physical exertion, particularly outdoors, and particularly if they experience symptoms. People with asthma may find they need to use their reliever inhaler more often. Older people should also reduce physical exertion. | Anyone experiencing discomfort such as sore eyes, cough or sore throat should consider reducing activity, particularly outdoors. |
| Very High (10) | Adults and children with lung problems, adults with heart problems, and older people, should avoid strenuous physical activity. People with asthma may find they need to use their reliever inhaler more often. | Reduce physical exertion, particularly outdoors, especially if you experience symptoms such as cough or sore throat. |
2.2 DAQI Statistics
Figure 2 shows the evolution of the ozone DAQI across summer 2024 at Oxford St Ebbes. There were 7 days on which ozone exceeded the “Low” DAQI band; 06 April, 09 May to 12 May, 19 May to 20 May, 02 June, 25 June to 26 June, 19 July, and 29 July to 01 August. During these episodes, the DAQI for ozone reached a maximum of 6, which occurred on 30 July and 31 July.
Thankfully, Oxford St Ebbes did not reach either the “high” or “very high” bands during the summer ozone episodes. It spent around 11% of days from April to August in the “moderate” band, which has associated health guidance for at-risk individuals (Table 2).
Low
125
Moderate
15
High
0
Very High
0
3 Measured Concentrations
3.1 Air Quality Statistics
Table 3 provides a monthly summary for ozone measured at Oxford St Ebbes, including a distribution of the daily air quality index for each month.
| month | mean | min | max | value | Max 8hr Rolling Mean | DAQI | |
|---|---|---|---|---|---|---|---|
| days >100 | days >120 | ||||||
| April | 70.02 | 4.19 | 105.52 | 103.81 | 1.00 | 0 | |
| May | 59.51 | 1.13 | 136.36 | 128.71 | 6.00 | 2 | |
| June | 57.38 | 1.55 | 136.31 | 132.75 | 3.00 | 1 | |
| July | 48.74 | 0.60 | 156.41 | 148.49 | 4.00 | 2 | |
| August | 51.14 | 0.20 | 141.25 | 106.20 | 1.00 | 0 | |
3.2 Hourly Mean Values
The hourly ozone concentrations measured at Oxford St Ebbes are shown in Figure 3.
4 Meteorology
4.1 Temperature Dependence
Every site in the AURN has accompanying modelled meteorological data obtained using the Weather Research & Forecasting (WRF) Model by Ricardo (Lingard et al. 2013), which can be combined with the measured meteorological data to demonstrate the temperature dependence on ozone. Figure 4 shows a hexagonally binned scatter plot of hourly modelled air temperature against ozone with a smooth trend fitted to the data. It shows that high ozone concentrations are broadly associated with high temperatures, with a particularly high gradient starting at roughly 20 ℃.
Lingard, Justin, Lorenzo Labrador, Daniel Brookes, and Andrea Fraser. 2013. “Statistical Evaluation of the Input Meteorological Data Used for the UK Air Quality Forecast (UK-AQF).” Ricardo-AEA. https://uk-air.defra.gov.uk/library/reports.php?report_id=770.
4.2 Air Mass Trajectories
Figure 5 shows binned data from the HYSPLIT forecast model (Stein et al. 2015). The plot illustrates where the air masses that affected Oxfordshire have travelled from, coloured by the ozone concentration at Oxford St Ebbes at time of arrival.
Stein, A. F., R. R. Draxler, G. D. Rolph, B. J. B. Stunder, M. D. Cohen, and F. Ngan. 2015. “NOAA’s HYSPLIT Atmospheric Transport and Dispersion Modeling System.” Bulletin of the American Meteorological Society 96 (12): 2059–77. https://doi.org/10.1175/BAMS-D-14-00110.1.
The specific approach used to create this map is Simplified Quantitative Transport Bias Analysis. You can read more about this in the openair book.
Air mass trajectories are an important factor on air pollution levels as they provide a useful indicator of the likelihood of transboundary air pollutants, many of which could be ozone precursor species. Air coming from the west is likely to be mainly clean and good pollution dispersion conditions (wind and precipitation), whilst air masses from the south and east can bring more settled conditions and also pick up background emissions from mainland Europe.
The map shows that the highest concentrations of ozone are associated with air masses arriving in Oxfordshire from over Northern Europe (countries like Belgium, the Netherlands, Germany, and Poland) and Spain. These have potentially picked up ozone-producing pollutants from industrial activity, exacerbating any ozone episodes experienced in the UK. Conversely, lower concentrations are associated with “cleaner” air masses arriving from over the Atlantic ocean.
5 Summary
In 2024, Oxfordshire experienced elevated ozone levels. This included the Oxford St Ebbes Automatic Urban and Rural Monitoring Network site in Oxford town centre, which reached “moderate” pollution levels on 15 days (Figure 2). Elevated ozone can be attributed to dry and sunny weather (Figure 4), with easterly wind carrying ozone precursors over from mainland Europe (Figure 5).
Throughout August 2024, O3 concentrations in Oxford have fluctuated within the “low” air quality index band. The changing meteorology which coincides with the UK entering the autumn and winter months makes any further ozone episodes in 2024 unlikely.