Belsize Air Quality – Questions and Answers

Posted on 16/8/2020

The survey was funded by the Community Infrastructure Levy and Belsize Society was supported by Camden Council’s Air Quality Officers, to whom we owe our thanks. The coronavirus lockdown meant we could not hold the planned public meeting with Camden’s officers to discuss the survey results so instead Tom Parkes, Senior Air Quality Officer, kindly responded to questions submitted by the volunteers:

Q: The legal limit for NO2 (40µg/m3) applies to bias corrected average annual data. Is it not of concern, however, that every one of the sites tested showed the limit was exceeded for some or many months?

A: Not necessarily – NO2 levels vary throughout the year in response to weather conditions (e.g. low wind speeds reducing ground layer mixing) and heating demand. NO2 is almost always higher in winter and especially at residential locations where a greater portion of overall NO2 emissions are from boilers. The 40µg/m3 limit is for annual mean exposure and it is assumed that the actual NO2 levels will drop above and below this at certain times. If we had one particular month where the NO2 concentration was extremely high compared to other months then this might cause some short-term health effects such as exacerbation of existing respiratory conditions (such as asthma etc.) and would indicate that something awry had happened locally (e.g. a local generator or roadworks, or persistent idling vehicles).

Q: More generally, is Camden Council concerned that there are many locations with several months where the raw measurements are above 40µg/m3?

A: The individual months have not had the bias adjustment factor applied, so they are likely a slight overestimate of the actual NO2 level. However, short- or medium-term exposure to elevated concentrations of air pollution may still trigger the symptoms of existing respiratory conditions. Therefore while the raw month-average NO2 concentrations measured in this survey are not unexpected for residential areas in London, the data still indicate that air pollution may impart a more significant effect on respiratory health during certain times of the year.

Q: The Maresfield Gardens / Nutley Terrace site is not a constantly busy road but nor is the number of boilers in the vicinity very high given the immediate built environment. So is there another explanation for the pattern found in the survey for Site 1?

A: This was the least polluted of the survey sites and at lower concentrations it can be more difficult to infer the pattern. However NO2 levels will always be a product of local emissions with a background contribution from longer-range sources of NO2 and its precursor chemical species (e.g. there is a complex atmospheric relationship between ozone and NO2, as well as volatile organic compounds from other sources). Nevertheless this site does exhibit the seasonality described above.

Q: How does Belsize Park compare with other areas of London and elsewhere insofar as information exists?

A: These results are fairly typical of predominantly residential areas in London. The area is outside the central area where even residential streets may have NO2 levels above the National Air Quality Objective 40µg/m3 annual mean limit. Air quality continues to improve throughout London and I strongly suspect this is the same in Belsize Park. London has comparatively ‘clean’ air compared to many other major cities, but that doesn’t detract from the fact that air pollution in London and the UK still imposes a significant mortality and quality of life burden which we need to address. It also disproportionately affects deprived communities: there is a very clear demographic and equalities element to air pollution.

Q: Given these results, does Camden have any estimates that would allow us to infer which, if any, of our locations are likely to breach the WHO/EU rule of a one-hour 200 µg/m3 limit not to be exceeded more than 18 times a year?

A: If the NO2 annual mean at a diffusion tube site exceeds 60µg/m3 it is assumed that the short-term National Air Quality Objective 200µg/m3 one-hour limit has been exceeded. That said, our Euston Road automatic monitoring site measured an annual mean of 70µg/m3 but only exceeded the one-hour limit seven times during the calendar year. The only Belsize Society monitoring site with an annual bias-adjusted mean above 40µg/m3 was Pond Street / Fleet Road and that measured well below 60µg/m3. Therefore, it is very unlikely that the 200µg/m3 one-hour limit was exceeded at this or any of the other monitoring locations at any point during 2019.

Q: If timed recordings had been possible, some sites (Maresfield Gardens / Nutley Terrace and Eton Avenue, for example) may well have indicated that most NO2 emissions are linked to school run traffic to independent schools in the vicinity, with a reduction in air quality particularly at the start and end of the school day during term time. If it were possible, it would be useful to do some time-specific monitoring near schools. Diffusion tubes, while cheap, are blunt measuring instruments. Could a more detailed survey be done with commercial sensors as a future study?

A: Commercial ‘low cost’ sensors are still expensive and also have issues with uncertainty, replicability etc. Diffusion tubes all perform the same and allow us to compare like-for-like across many sites and over long periods of time, despite the lack of temporal granularity. The Council is very aware of the air quality impact of traffic flows to and from schools in Camden and the Frognal / Fitzjohn’s / Hampstead area in particular. Colleagues in Transport Strategy continue to work on schemes to protect health by limiting vehicular access to congested school streets at drop-off and pick-up times, while supporting behaviour change initiatives to encourage uptake of alternative modes of transport.

Q: What range of possible actions may Camden take in response to these results, especially after the coronavirus emergency is over and, presumably, air pollution returns to the high levels experienced last year?

A: Camden’s Transport Strategy (CTS) seeks to achieve a borough-wide reduction in annual traffic mileage by promoting and facilitating a modal shift towards journeys on foot and by bike (or other means of active travel). The CTS was developed in tandem with five other action plans, including a Walking & Accessibility Action Plan, a Cycling Action Plan and a Freight Action Plan, all of which will have an impact on vehicular traffic and air quality. Furthermore, the Electric Vehicle Charge Point (EVCP) Action Plan sets out the intention for the deployment of EV infrastructure in Camden, which will help to reduce NO2 pollution.

Camden’s Clean Air Action Plan, CTS and Climate Action Plan are mutually supportive and will all deliver improvements to air quality in Belsize Park and elsewhere in Camden. It’s crucial to note that everybody contributes to air pollution, so it requires a collective effort to understand how we impact air quality and how it affects us, and for everyone to try to play their part in protecting personal and public health. For instance, avoiding burning wood or coal fuels at home (or garden waste), avoiding driving wherever practicable, insulating homes, replacing boilers with ultra-low NOx systems or, better still, heat pumps or electric heating alternatives, will all help to improve air quality.