Frackbox Hardware

The Citizen Sense Frackbox was designed in response to the concerns of citizens in northeastern Pennsylvania about the effects of the hydraulic fracturing industry on air quality. The Frackbox sensor kit is housed in a US mailbox. It is designed to be placed at sites near fracking infrastructure and at the intersections between infrastructure and peoples’ homes.

The Frackbox monitors criteria air pollutants, including nitrogen oxide (NO), nitrogen dioxide (NO2), and ground-level ozone (O3). The Frackbox also senses volatile organic compounds (VOCs), including benzene, toluene, ethylbenzene and xylene (BTEX), along with halomethanes and glutaraldehyde.

In addition, the Frackbox senses humidity, temperature, and wind direction. Each Frackbox can be built with a camera, and can include custom sensors specific to site conditions, including particulate matter (PM 2.5) (using a Speck), wind speed, noise and methane (CH4).

The Frackbox is designed to asynchronously record sensor data, to save data to a database and csv file, and then to post data periodically to the Citizen Sense platform (a private site used during the course of the monitoring period, which is no longer available). The Frackbox runs on Linux, an open-source operating system. It uses 5-volt power supplied either by USB or solar panels, and has a cellphone network connection for transmitting data.

Frackbox Contents

The Frackbox is designed to include the following sensors, electronics and monitoring equipment:

• Raspberry Pi
• Alphasense NO2 A4 (electrochemical sensor)
• NO A4 (electrochemical sensor)
• O3 A4 (electrochemical sensor)
• PID (non-dispersive infrared sensor for total VOCs)
• ND-100s GPS dongle
• Huawei dongle
• CH4 PrimePell (non-dispersive infrared sensor)
• Maplin replacement wind-direction and wind-speed sensors
• Sparkfun sound detector

Frackbox Wiring Layout and Sensors

Electrochemical Sensors NO, O3, NO2: The air quality sensors used in the Frackbox are manufactured by Alphasense. Alphasense air sensors are developed in partnership with the University of Cambridge specifically for air quality applications. These sensors are amperometric gas sensors and are made up of four working electrodes in electrical contact with the electrolyte via wetting filters.

The electrochemical sensor nodes used in the Frackbox are designed to take advantage of recent advances in gas sensor developments. Improved sensitivity of gas sensors, low power requirements and portability were some of the key factors considered in the design of the electrochemical sensor nodes.

Although practical application of the sensor involves measuring very small currents (nanoampere, nA), the electronic design of the air quality sensor instruments amplifies this signal and converts it to digital outputs, which are then converted to concentration units (ppb/ppm) using known calibration factors generated for each sensor. For the latest recommendation on converting sensor responses to ppb/ppm and calibration response factors please contact the manufacturers.

Detection Level
< 5 ppb (O3 and NO) and < 5 ppb for NO2

Start-up time
NO: start-up time of ten hours
NO2 and O3: start-up time of ten minutes

Measurements
There is some cross interference in the gases monitored, although we worked with a NO2 sensor developed summer 2013 that had reduced interference levels. For instance, when high levels of O3 are detected, there may also be a drop in NO2 that will need to be accounted for due to cross interference. The cross interference of O3 should be accounted for in the data processing.

The Frackbox has the potential to have accuracy to within 5 ppb with regular calibration. However, in its early prototype stage the Frackbox may have larger detection differences of around 20 ppb (sometimes more) between the Frackboxes. The national error standards fall between 10 to 40 ppb (depending upon the country where air quality monitoring is undertaken). Due to these detection differences, it is more useful to use the Frackbox to observe changes and identify sources, rather than to use the measurements as direct comparisons to regulatory standards.

Photoionization detector (PID sensor for total VOCs)
The PID sensor is also being used by a number of air quality sensing projects undertaken by atmospheric scientists. It is useful but also it has its limitations. The PID sensor can be calibrated to respond to a number of VOCs, including BTEX, to give a total VOC reading. It is not a selective sensor, however, and will require calibration in relation to separate VOCs.

Detection level: < 5 ppb
Start-up time PID: start-up time of 5 minutes

Calibrating Sensors

As these sensors are designed for measuring air quality in the field, to calibrate the sensors, and establish the sensor zero, you can pass zero air over the sensors. This process does not have to occur in an air-tight chamber. You can use a canister of aero air together with a flow meter, tubing and funnel. Do not use a plastic funnel as we did on our first attempt, as this approach will produce VOCs (it is a useful way to test the PID, however).

Sourcing Parts

Below is a shopping list for the contents of the Frackbox. The mailbox was sourced from eBay.

• RaspberryPi Model B+: Cost: £24 | Description: A small computer for DIY electronics. The Model B+ is the final revision of the original Raspberry Pi. It replaced the Model B in July 2014. It has 4 USB ports, micro SD card slot and lower power consumption.
• Huawie E355 and E8231 3G Dongles | Cost: £33 (second hand) | Description: A 3G dongle plus Wi-Fi modem and router which creates its own Wi-Fi hotspot. The code written to connect the RaspberryPi with these dongles is specific to the  E355 and E8231 models, although it is feasible they will work with other Huawie dongles.
• GPS Dongle | Cost: £25 | Description: The ND-100S USB GPS dongle is a GPS receiver. It has low power consumption and a highly sensitive SiRF Star III GPS antenna.
• Alphasense breakout board with sensors | Cost: £642.40 | Description: A breakout board that holds four Alphasense sensors which measure NO, NO2, O3, and VOCs (PID).
• Abelectronics analog to digital converter (ADC Pi V2.2) | Cost: £20 | Description: An 8-channel 17-bit analogue to digital converter designed to work with the Raspberry Pi platform. The ADC Pi is based on two Microchip MCP3424 A/D converters each containing 4 analogue inputs with up to 18-bit resolution.
• Real time clock (RTC) module | Cost: £10.50 | Description: A breakout board for the DS1307 chip used to keep track of  the current time. Includes a coin cell battery that will run the RTC for 9 years without an external 5V power supply.
• MCP3008 analog to digital converter | Cost: £1.86 | Description: Adds 8 channels of 10-bit analog input. Communicates over Serial Peripheral Interface (SPI).
• Wind direction sensor N96FY/N96GY | Cost: £9.99 | Description: Wind direction sensor used within Maplin’s wireless weather stations.
• N96FY Wind speed sensor | Cost: £2.49 | Description: Wind speed sensor used with Maplin’s wireless weather stations.
• Temperature and humidity sensor | Cost: £28.99 | Description: A DS18B20 temperature and humidity sensor which uses an Inter-Integrated Circuit (I2C) communication protocol.

The estimated cost for assembling the Frackbox is ~ GBP 800 (excl. labor).

More Information

The Frackbox is a Citizen Sense prototype. Contact us for more details, or to share your versions of the kit should you attempt to make one. You can view the installation locations for the Frackboxes here. You can view and analyze the data collected from the initial Frackbox installations with our Frackbox Data Analysis Toolkit.

Images: Frackbox hardware and wiring diagrams, Kelly Finan for Citizen Sense (2015). All other images Citizen Sense (2014-2015).