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All across the world, PurpleAir air quality sensors have been growing in popularity due to their easy setup and low unit cost which allows for the rapid deployment of local high-density air quality monitoring networks which are also part of the larger global PurpleAir network. Indeed, PurpleAir takes much of the burden out deploying such a network by not only providing the ready-to-deploy sensor units (equipped with two PM sensors, meteorological sensors, wifi capabilities, AC power), but they also provide the infrastructure for the transfer, handling, storage, and visualization of data. For each sensor, the end-user merely has to provide power, wifi, and register the sensor with the PurpleAir website. Once that is done, the user can immediately start viewing and downloading data from the PurpleAir website for their own analysis.
Traditionally, air quality monitoring is done by large and expensive monitoring instruments that only large entities or organizations like the government can afford. Think tens of thousands of dollars per instrument. Due to the high costs, even large entities may only be able to a few to cover a large region. On the other hand, one Purple Air sensor costs about $300 at the time of this writing, which is less than the typical smartphone. At such a low-cost, curious individuals can even choose to purchase and setup one for personal purposes, but their sensor would still be contributing to the global PurpleAir network making it more robust overall. To give an example of the implications sensor costs have on network size, TCEQ utilizes regulatory sensors, but it only has three instruments to measure particulate matter for the whole Austin region. On the other hand, the low-cost of the PurpleAir sensor has allowed IEL to deploy sixteen of them just on the UT Austin main campus.
The main reason the PurpleAir sensors are so inexpensive is because they use a less accurate method of measuring particulate matter. Whereas regulatory sensors may "weigh" the particulate matter in the air, PurpleAir sensors use a laser to measure particulate matter by counting the number of light flashes caused by particles passing through the laser. As such, the PurpleAir sensors are less accurate due to the use of an optical rather than a gravimetric method of measuring PM. For instance, even something such as high humidity can introduce errors into PM measurements by PurpleAir.
Although air quality regulators may balk at using PurpleAir data in their work, PurpleAir sensors offers the general public a "good enough" understanding of local air quality, and the potential for deployment in high-density or hyperlocal networks may offer additional benefits.
In the semester of Fall 2019, a network of 16 PurpleAir sensors were deployed on the UT Austin campus. Talk to Hagen for more info.
So once the network was deployed, the data started uploading to the PurpleAir website where it was publicly available. However, no one at IEL made use of this data for a while, and it was not a focus of anyone's paper.
Under the supervision of a graduate student and in rare occasions the professor, the undergrad will try to explore questions that they and the graduate student create through data analysis in Python.
- Creating a model to correct PurpleAir data to better match data from regulatory air quality sensors such as those managed by TCEQ or the EPA.
- Collocation in-field or in-lab [pending equipment]
- Identifying temporal or spatial trends
- Sensors may not be located far enough away from each other to pick up significant differences
- Limited long-term data due to sensors being set up last year
PurpleAir is a company that created a low-cost air quality sensor that can be deploy en-masse. They have recently been growing in popularity as a result.
- Low-cost, less than $300 per sensor.
- Can be deployed by consumers or everyday people.
- WiFi connected allowing deployment anywhere there is power.
- Purple Air provides limitless cloud storage and allows access through their website and REST Api.
- They also provide a map that allows users to view data from PurpleAir sensors all over the world. Open access data.
- Compact size, fits in hand.
- Reasonably accurate when averaged over frequencies greater than hourly.
- Cheap cost and relative portability means that the can be deployed in high-quantities to canvass a large geographical area.
- Real-time data available, no regulatory middleman
- Available for both indoor and outdoor use.
- Some models carry two onboard sensors to allow for cross-validation of data.
- Temperature and humidity sensor also included.
- Sensors may not be as accurate as regulatory sensor with humidity causing values to read high.
- Sensor cannot be calibrated for local air composition, and the manufacturer's correction method, which is calibrated for air in China, is unknown
- No batteries built-in.
- Requires access to wifi, mobile data not supported?
- No on board storage?