Each of our weather stations are fitted with temperature, humidity, rainfall, and wind sensors along with WiFi networking capabilities to transmit data in real-time. Some of our weather stations are also fitted with air quality sensors. We use Vaisala’s weather and air quality sensors which are ideal for installation and use in Sydney’s schools due to their reliability, compact size, and low power consumption. They can be installed quickly in out-of-the-way locations and require low maintenance, while providing research quality data. The two main Vaisala instruments installed by SWAQ are the Weather Transmitter WXT530, for collecting weather data, and the Air Quality Transmitter AQT420, for collecting air quality data.

The Vaisala WXT530 Weather Transmitter. Source: Vaisala.

The Vaisala AQT420 Air Quality Transmitter. Source: Vaisala.

Weather Sensors

Our weather stations can collect and transmit data for six of the most common weather variables: air pressure, temperature, humidity, rainfall, wind speed and wind direction. They also use a built in analog to digital converter, allowing all weather data to be directly transmitted online for use by students and researchers alike.

Thermometer

Air temperature, the measure of how hot or cold it is, is measured using temperature sensors called thermometers. Our weather stations use capacitive ceramic temperature sensors. A capacitor is simply a device that stores electrical energy and releases this energy back to the circuit when required. The capacitance of the sensor responds to changes in air temperature, and this electrical response is converted to an air temperature reading.

Barometer

A barometer is used to measure local changes in air pressure. In SWAQ weather stations, the barometer is a micromechanical sensor comprising a capacitor and a silicon membrane. As the surrounding air pressure changes, the silicon membrane bends and this in turn changes the capacitance of the sensor. The changes in capacitance are detected electrically and converted into a pressure reading.

Hygrometer

Humidity, or the amount of water vapour present in the air, is measured using a hygrometer. In our weather stations, the hygrometer is a capacitive sensor made up of a polymer layer between two electrodes. The polymer layer absorbs or releases water depending on the surrounding relative humidity, and this absorption or release modifies the capacitance of the sensor. The sensor measures these changes in capacitance and converts it to a humidity reading.

The temperature, pressure and humidity sensors are all housed inside a radiation shield which protects the sensors by reflecting radiation from surrounding rooftops and surfaces, while still allowing air flow across the sensors.

Rain sensor

Rainfall is measured using a precipitation sensor which detects the impact of individual raindrops. The signals from the impact are proportional to the volume of the rain drops and can be converted directly to an accumulated rainfall measurement. The sensor can measure total accumulated rainfall, rain intensity, duration of a rainfall event, and can even distinguish hailstones from raindrops.

SWAQ weather and air quality sensors at Luddenham Public School.

SWAQ weather and air quality sensors at Glenorie Public School.

Anemometer

Wind speed is typically measured using an instrument called an anemometer, while wind direction is often measured using a wind vane. Anemometers commonly have three or four hemispherical cups attached to horizontal arms which are mounted on a vertical rod. When the wind blows, the cups begin to rotate, spinning the vertical rod. The stronger the wind, the faster the rod will spin. The anemometer records the number of rotations of the vertical rod, which is used to calculate wind speed.

Wind vanes often look like an arrow mounted on a vertical pole. As the wind blows they rotate and point into the wind. For example, if wind blows from the east, a wind vane will point eastward. An alternative to anemometers and wind vanes, are wind socks. These textile tubes, often seen at airports (and even in our logo), give an indication of wind direction by pointing in the direction that wind blows, as well as indicating relative wind speed. The fuller the wind sock, the faster the wind speed.

Unlike these traditional instruments, both wind speed and direction in SWAQ weather stations are measured using a sensor with ultrasound technology. The wind sensor contains three transducers (devices that convert energy from one form to another) that produce ultrasonic signals. The transducers point upwards towards the sky and are arranged in a triangular pattern with equal spacing between them. Wind speed and direction are determined by measuring the time it takes for the ultrasonic signal of one transducer to travel to the other transducers.

The weather transmitter housing and sensor locations. Source: Vaisala WXT530 Manual.

A traditional cup anemometer. Source: Wikimedia Commons.

Air Quality Sensors

The Air Quality Transmitter AQT420 can collect and transmit data for the most common gaseous air pollutants: nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), and ozone (O3), as well as small particle pollutants suspended in the air, known as Particulate Matter. Our air quality sensors measure both PM2.5 (Particulate Matter less than 2.5 micrometers) and PM10 (Particulate Matter less than 10 micrometers) at 10 minute intervals, while the gaseous air pollutants are measured every minute. While all six pollutants mentioned are measured by our air quality sensors, only NO2, O3, PM2.5 and PM10 are currently shown on the data portal.

The air quality transmitters used by SWAQ make use of advanced algorithms and electrochemical sensors to measure gas concentrations while accounting for ambient conditions such as temperature and humidity which can affect the results. Gases sampled by our air quality sensors react with an electrochemical cell and create a weak electric current. The gas content in the air is calculated by applying an algorithm to the measured electric current. Particulate Matter on the other hand, is measured using a laser particle counter. When the laser hits a particle in the air it is scattered, and the intensity of this scattering, combined with digital signal processing techniques, is used to measure the size and concentration of Particulate Matter. As for the gaseous pollutants, Particulate Matter concentration is affected by ambient conditions such as high humidity, and must be compensated by these measurements. We always install a weather station alongside our air quality sensors so we can monitor weather variables to understand how local weather conditions, such as wind speed and direction, influence local air quality.