The sensor nodes incorporate multiple off-the-shelf gas sensors, a compact low-cost optical particle counter, a combined GPS receiver and GPRS transmitter and a weather station. They are powered by an external lead-acid battery pack which enables the unit to run continuously for several months before recharging. The gas sensors are supplied off-the-shelf by Alphasense and allow the measurement of NO, NO2, CO, O3, CO2, volatile hydrocarbons and SO2 concentrations. The optical particle counter was designed and built at the Centre for Atmospheric and Instrumentation Research at the University of Hertfordshire. This measures aerosol concentrations in the form of 16-bin histograms covering the size range 0.38-17μm. The on board weather station reports local air temperature, relative humidity, wind speed and wind direction.
The air quality data collected on the devices are firstly labelled by GPS location and time and are then stored in situ before transmission via GPRS to a central server for post-processing and on or off-line analysis. A PIC microcontroller handles the collection of data from the sensors and the interface to the on board storage. The combined GPS/GPRS facility is provided by a Telit GM862 unit running a custom written Python script.