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Appendix B: Instrumental Setup for Measuring
Emissions
A remote sensing device is used for measuring the exhaust emissions
from gasoline vehicles. As shown in Figure B.1, the gas scope (GS) and
the retro reflector (RR) are put on either side of the road and aligned
with each other. The gas scope emits infrared and ultraviolet beams
(IR/UV), which run horizontally across the road and are reflected by
the RR back to the GS. When a vehicle passes by, the light beam goes
through the exhaust gas plume coming out of the vehicle. Part of the
light beam will be absorbed by the exhaust. When the beam is reflected
back to the GS, both infrared and ultraviolet rays will have been
reduced to some degree. After measuring the degree of weakening
of the light intensity, the light intensity signal is then converted to an
electric signal, which is converted by the sensor and data acquisition
board to a digital signal. The digital signal is then sent to the central
processor, and the data on the composition of the exhaust emissions
from each passing vehicle is obtained.
During the testing process, the length and density of the exhaust
plume changes greatly due to several factors, including the height
of the exhaust pipe (relative to the road), the wind speed, and the
turbulence at the rear of the vehicle. Hence, the remote sensing system
cannot detect the concentration of the exhaust directly. The instrument
measures the composition of the exhaust (e.g., CO, HC, and NO to
CO2 ratio (CO/ CO2, HC/CO2, NO/CO2), which is constant for a
given exhaust plume. The concentration of the exhaust is calculated
and represented by volume: CO (per cent), HC (ppm), NO (ppm). For
the INSPECTOR IV ® system, the range of accuracy of CO and CO2
concentrations by volume is ±0.25 per cent. When the CO and CO2
concentrations by volume are greater than 3 per cent, the error is 15
per cent of the measured value. The range of error of the HC and NO
concentrations by volume is 250 ppm to –250 ppm or 15 per cent of the
measured value (whichever is greater).
The system is equipped with a low-energy laser velocimeter, which
can measure both the running speed and the acceleration of a vehicle
simultaneously. A high-speed colour digital camera is also placed on
one side of the road to take a shot of the vehicle’s licence plate and
acquire further information. The measured values of the running
speed and acceleration as well as the image signal is sent to the central
processor. The speed accuracy is ± 1km h–1, and the accuracy of the
acceleration is 0.5 km h–1s–1. During this process, the meteorological
conditions such as temperature, humidity, wind speed and wind
168 Low Carbon Development in China and India
Emissions
A remote sensing device is used for measuring the exhaust emissions
from gasoline vehicles. As shown in Figure B.1, the gas scope (GS) and
the retro reflector (RR) are put on either side of the road and aligned
with each other. The gas scope emits infrared and ultraviolet beams
(IR/UV), which run horizontally across the road and are reflected by
the RR back to the GS. When a vehicle passes by, the light beam goes
through the exhaust gas plume coming out of the vehicle. Part of the
light beam will be absorbed by the exhaust. When the beam is reflected
back to the GS, both infrared and ultraviolet rays will have been
reduced to some degree. After measuring the degree of weakening
of the light intensity, the light intensity signal is then converted to an
electric signal, which is converted by the sensor and data acquisition
board to a digital signal. The digital signal is then sent to the central
processor, and the data on the composition of the exhaust emissions
from each passing vehicle is obtained.
During the testing process, the length and density of the exhaust
plume changes greatly due to several factors, including the height
of the exhaust pipe (relative to the road), the wind speed, and the
turbulence at the rear of the vehicle. Hence, the remote sensing system
cannot detect the concentration of the exhaust directly. The instrument
measures the composition of the exhaust (e.g., CO, HC, and NO to
CO2 ratio (CO/ CO2, HC/CO2, NO/CO2), which is constant for a
given exhaust plume. The concentration of the exhaust is calculated
and represented by volume: CO (per cent), HC (ppm), NO (ppm). For
the INSPECTOR IV ® system, the range of accuracy of CO and CO2
concentrations by volume is ±0.25 per cent. When the CO and CO2
concentrations by volume are greater than 3 per cent, the error is 15
per cent of the measured value. The range of error of the HC and NO
concentrations by volume is 250 ppm to –250 ppm or 15 per cent of the
measured value (whichever is greater).
The system is equipped with a low-energy laser velocimeter, which
can measure both the running speed and the acceleration of a vehicle
simultaneously. A high-speed colour digital camera is also placed on
one side of the road to take a shot of the vehicle’s licence plate and
acquire further information. The measured values of the running
speed and acceleration as well as the image signal is sent to the central
processor. The speed accuracy is ± 1km h–1, and the accuracy of the
acceleration is 0.5 km h–1s–1. During this process, the meteorological
conditions such as temperature, humidity, wind speed and wind
168 Low Carbon Development in China and India
