Low-Cost Aerosol Sensors
There are direct reading instruments for aerosols
that are based on the principle of light scattering.
Aerosol photometers measure the light scattered by many particles
which has been shown to correlate well with the mass concentration
of particles from 0.3 to 10 micrometers.
They cost approximately $2,500 to $8,000.
Optical particle counters measure the particle number concentration by size
from 0.3 to 10 micrometers.
They range in cost from $8,000 to $15,000.
Numerous vendors now offer small low-cost sensors.
Aerosol photometers typically cost less than $20.
There are also optical particle counters
that measure the size of individual particles.
They run from $25 to $300.
These sensors are limited in that
they require integration into a larger monitoring system
that provides power and enables communication.
They also require calibration.
Commercial vendors offer monitors with integrated low-cost aerosol sensors.
These monitors typically cost $150 to $300.
Many researches have assessed performance of low-cost sensors
and monitors by comparing their output to reference devices.
An example is shown in the figure at right.
Each monitor has unique operating characteristics
and operating ranges.
For all of them,
the output signal is a function of particle mass concentration.
For example, in the plot, the Foobot compares well to the reference
over a large concentration range up to 1,000 micrograms per meter cubed.
In contrast, the AirBeam does not respond
to mass concentrations greater than 150 micrograms per meter cubed.
The reason for this discrepancy
is unknown, but we suspect that there
are too many particles in the detection region.
The output signal is also a function of aerosol refractive index.
White particles, such as salt, scatter more light than absorbing black particles such as soot.
Morphology of particles can also impact the output signal.
Precision of these sensors is often far worse
than their more expensive counterparts.
The State of California operates an air quality sensor performance evaluation center
that serves as an excellent source of information
about accuracy and precision.
These sensors open up new possibilities for assessing
exposures to harmful contaminants.
Their low cost allows the purchase of many sensors.
The data from many sensors can provide spatiotemporal
information unavailable with conventional instruments.
This type of data can be used to identify
areas of higher exposure that would benefit
from the application of control technologies.
At right, the map shows particulate matter
measured with low-cost sensors at many points on a factory floor.
These areas of high concentration, indicated in red,
are above workplace exposure levels
and require mitigation.
Low-cost sensors have also been used to detect hazards outdoors.
Here, each dot represents a sensor
that responds to wildfire smoke.
This type of information can be used by
the public to help identify when conditions are hazardous.
Other examples include ambient air
pollutant concentrations over time and averaged,
live air quality maps,
citizen and community science,
and, lastly, personal exposures by location, which is depicted at right.
In this image, the colored line indicates
a person's path through the city streets.
The low concentrations are shown in blue,
and the high concentrations are shown in yellow and red.
There was clearly a spike at one intersection
and on a major road.