S=N ¼
n s
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi
4kT R s þ n 2
n þ i n R s
ð
Þ
2
q
ffiffiffiffiffiffi
Df
p
where k is Boltzmann’s constant, T is absolute
temperature, R s is output impedance, and Df is
the frequency bandwidth in Hz. This formula
clearly shows that the signal-to-noise ratio can
be improved by reducing T, R s , and Df.
The Shannon-Hartley theorem [41] defines the
channel capacity, C, which is a measure of how
quickly information can be transmitted over a
communication channel in bits per second, and
is expressed as [42]
C ¼ B log 2 1 þ S=N
ð
Þ
B is the bandwidth of the channel in Hz.
There are several methods for modeling sensors’ noise, but the simplest technique is the Allan
Variance method which was proposed in 1966 by
Low-Cost Sensors for Indoor and Outdoor Pollution, Table 2 (continued)
Pollutant Sources [26]
Low-cost sensor applications
Main effects [24]
VOC
Agriculture
Woodlands
Volatile
consumer
products
General solvent
use
Transportation
Printing/surface
coating
Industrial
Residential
City pollution map, personal occupational
exposure, e.g., painters, traffic police,
parking attendants [33]. Shipping
container and new building monitoring
[34]
Climate change
Health: Nose, eye, and throat irritation,
loss of coordination, headaches, damage
to kidney, liver, and central nervous
system, cancer
SO 2
Combustion of
sulfurcontaining fossil
fuels
Volcanoes
Monitor ports and shipping routes,
monitor volcanoes [35]
Climate change, acid rain
Health: Irritates the skin and membranes
of the nose, eyes, and lungs
N 2 O
Agriculture
Fossil fuels
combustion
Industrial
processes
Biomass burning
Atmospheric
deposition
Human sewage
Agricultural emission monitoring [36, 37] Climate change
Health: Vomiting, headache, increased
sleepiness, and excessive sweating or
shivering
Low-Cost Sensors for
Indoor and Outdoor
Pollution, Fig. 2
Amplifier and signal source
n s with noise sources n n and
i n [40]
Low-Cost Sensors for Indoor and Outdoor Pollution
429
n s
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi
4kT R s þ n 2
n þ i n R s
ð
Þ
2
q
ffiffiffiffiffiffi
Df
p
where k is Boltzmann’s constant, T is absolute
temperature, R s is output impedance, and Df is
the frequency bandwidth in Hz. This formula
clearly shows that the signal-to-noise ratio can
be improved by reducing T, R s , and Df.
The Shannon-Hartley theorem [41] defines the
channel capacity, C, which is a measure of how
quickly information can be transmitted over a
communication channel in bits per second, and
is expressed as [42]
C ¼ B log 2 1 þ S=N
ð
Þ
B is the bandwidth of the channel in Hz.
There are several methods for modeling sensors’ noise, but the simplest technique is the Allan
Variance method which was proposed in 1966 by
Low-Cost Sensors for Indoor and Outdoor Pollution, Table 2 (continued)
Pollutant Sources [26]
Low-cost sensor applications
Main effects [24]
VOC
Agriculture
Woodlands
Volatile
consumer
products
General solvent
use
Transportation
Printing/surface
coating
Industrial
Residential
City pollution map, personal occupational
exposure, e.g., painters, traffic police,
parking attendants [33]. Shipping
container and new building monitoring
[34]
Climate change
Health: Nose, eye, and throat irritation,
loss of coordination, headaches, damage
to kidney, liver, and central nervous
system, cancer
SO 2
Combustion of
sulfurcontaining fossil
fuels
Volcanoes
Monitor ports and shipping routes,
monitor volcanoes [35]
Climate change, acid rain
Health: Irritates the skin and membranes
of the nose, eyes, and lungs
N 2 O
Agriculture
Fossil fuels
combustion
Industrial
processes
Biomass burning
Atmospheric
deposition
Human sewage
Agricultural emission monitoring [36, 37] Climate change
Health: Vomiting, headache, increased
sleepiness, and excessive sweating or
shivering
Low-Cost Sensors for
Indoor and Outdoor
Pollution, Fig. 2
Amplifier and signal source
n s with noise sources n n and
i n [40]
Low-Cost Sensors for Indoor and Outdoor Pollution
429