Skip to content

Bath Air Quality Sensor Data

Leigh Dodds edited this page Apr 20, 2015 · 1 revision

This page provides documentation for the Bath air quality sensor data available in the Bath: Hacked data store.

There are two air quality datasets:

There’s also a third dataset that contains the names and geographic locations for the 5 sensors

How is the data collected?

There are five air quality sensors situated around Bath, within the Air Quality Management Area.

The sensor locations are shown on a map.

The sensors are not identical. Different sensors measure different aspects of air quality.

What data is collected?

Nitrogen dioxide (NO2): This is the main pollutant of interest. A gas that is directly emitted and created after emission of NOx. Most of the major road network in Bath exceeds the national objective limit for an annual average of 40 micrograms per cubic metre (μg/m³). An hourly limit of 200 μg/m³ is not to be exceeded more than 18 times a year. The Bath Air Quality Management Area roughly covers the areas where this objective is exceeded. No other pollutants exceed the objectives in Bath and North East Somerset.

Oxides of nitrogen/nitrogen oxides (NOx): This encompasses nitric oxide (NO) and nitrogen dioxide (NO2).

Particulate matter (PM10): Particulate matter with diameter of 10 micrometres or less. Objective limit of 40 μg/m³ as an annual average is not exceeded in Bath. 24 hourly limit of 50 μg/m³ not to be exceeded more than 35 times a year (also not exceeded).

Ozone (O3): aka Trioxygen. Greenhouse gas. Formed by the reaction of sunlight on air containing hydrocarbons and nitrogen oxides that react to form ozone directly at the source of the pollution or many kilometers downwind. National air quality objective is 100 μg/m³ not to be exceeded more than 10 times a year as measured over an 8hr mean.

Carbon monoxide: National air quality objectives of 10 μg/m³ as a running 8 hour mean.

A deeper explanation for what air pollutants mean for public health in BANES is available on the B&NES Wiki.

How often is the data updated?

The sensors measurements are collected from the sensors and added to a repository at B&NES at 15-60 minute intervals. The data is then published to the live store at 1-4 hour intervals.

So while this is a live, continuously updated dataset, there is a lag between the recordings and the data being available.

Obviously the historical data won’t change, its an archive of previous readings made available for further analysis.

How is the data organised?

Data is recorded in each datastore in raw units of measure

Column Name Column ID Units Description
ID id N/A Unique identifier for the reading
DateTime datetime N/A Time reading was recorded in GMT
Sensor Location Name sensor_location_name N/A Name of sensor. The names match the entries in the sensor location dataset.
Sensor Location Slug sensor_location_slug N/A Identifier for sensor
Sensor Location sensor_location N/A Latitude and longitude for the sensor, i.e. where the reading was taken
NOx nox ppb Nitric oxide and nitrogen dioxide.
NO no ppb Nitric oxide
NO2 no2 ppb Nitrogen-dioxide
CO co ppm Carbon monoxide
PM10 pm10 μg/m³ Particulate matter with diameter of 10 micrometres or less
O3 03 ppb Ozone

The last 6 columns are the sensor readings. A column will be empty if the sensor does not record that type of measurement.

The units of measurement are:

  • μg/m3 = micrograms per cubic metre
  • mg/m3 = milligrams per cubic metre
  • ppb = parts per billion
  • ppm = parts per million

What quality control is carried out on the data?

All of the readings are raw data recorded directly from the sensors. It has not been adjusted to account for errors, monitor drift or failures, some data may therefore show unusual results (e.g. negative data or spikes).

Are there any known issues?


Further reading

The DEFRA air quality site has some useful background resources, this page has some links to information on causes and effects of air pollution.

DEFRA also provide some guidance on official reporting of air quality indexes, and detailed notes on the calculations.

Air quality indices should be calculated in μg/m³, using multipliers of measurement units. Specific colours should be used for each index. Outlier values (caused by maintenance) should be removed from averages. Some useful values have been made available as JSON.

The Air Quality Action Plan for Bath sets out how B&NES are working to improve air quality in Bath.