Remote Sensing Technology Helps Improve Urban Air Quality

Researchers from the University of Technology Sydney have demonstrated the effective use of remote sensing technology for the fast and accurate detection of highly polluting vehicles in urban environments.

Remote Sensing Technology Helps Improves Urban Air Quality.

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Using emission datasets from remote sensing, air quality monitoring and chassis dynamometer testing, the researchers found that a large proportion of petrol and LPG vehicles fail to meet emission standards.

Challenges with current environmental enforcement schemes include difficulties in setting appropriate cut points and a lack of data pertaining to diesel vehicles. Remote sensing technology is primed to address these challenges.

Remote sensing equipment uses a sensor and light beam to measure chemical concentrations in the exhaust as a vehicle drives past. A camera records the licence plate, so vehicles can be identified for inspection and repair.

Prof. John Zhou, Environmental Engineering, University of Technology Sydney

A Brief Primer on Remote Sensing Technology

Remote sensing describes the capture of information at a distance by instruments. Although the term is often applied in the context of geoscience and Earth observation, remote sensing has a wide range of applications, including military, commercial, social, environmental and humanitarian applications.

Charged particles in objects and the environment emit energy in the form of electromagnetic waves - i.e., light. This light travels at different frequencies (or wavelengths). The shorter wavelengths - such as ultraviolet light and x-rays - have higher energy, while the longer wavelengths - such as radio waves and infrared - have less energy.

As minerals, gases, metals and other elements absorb or reflect different wavelengths of light, they display unique spectral signatures. Thus, scientists can describe the physical and chemical properties of various elements using remote sensing.

Instruments are needed to detect all electromagnetic radiation that falls outside the visible spectrum.

Some sensors provide their own source of radiation. Objects and elements in the environment reflect this radiation which these sensors can subsequently analyze. These “active” sensors include radars, altimeters and scatterometers. They mostly detect microwave radiation. 

Other sensors simply capture the natural radiation from objects and elements in the environment. These “passive” sensors include spectrometers and radiometers. They mostly detect visible, infrared and microwave radiation.

In environmental and ecological studies, remote sensors are used to:

  • Monitor concentrations of greenhouse gases and CO2 emissions
  • Monitor biodiversity, water pollution and land degradation
  • Monitor agricultural and food production
  • Monitor land use, urban systems and public health

Remote sensing technologies provide quantitative data that helps address environmental, sustainability, economic and social challenges.

Enforcing Environmental Policies with Remote Sensing Technology

Road transport is a major contributor to air pollution across the world. According to The International Council on Clean Transportation, air pollution accounted for $1 trillion of health-related damages in 2015.

This is further aggravated by the fact that vehicle emissions will deteriorate as mileage accumulates, even if they meet emission standards when brand new.

Therefore, a large proportion of vehicles on the roads will emit substantially higher pollutants than standard estimates would lead us to believe. Identifying and removing these vehicles is therefore essential to the success of environmental protection policies around the world.

On-road remote sensing technology provides the opportunity for rapid, non-invasive and cost-effective detection of these vehicles.

Current remote sensing systems, however, provide only snapshot emissions of passing vehicles. For real-world, dynamic scenarios where factors such as acceleration and load need to be factored in, a serious research program is needed.

The researchers at the University of Technology Sydney collaborated with the Hong Kong Vocational Training Council and the Hong Kong Environmental Protection Department (HKEPD) to assess the remote sensing enforcement program already operating in Hong Kong.

They analyzed data sets obtained from remote sensing, chassis dynamometer testing collected between September 2014 and December 2018 and air quality monitoring.

The study identified 16,365 high-emitting LPG and petrol vehicles using remote sensing. Subsequently, 96.3% of these were repaired and thus were able to pass the Hong Kong Transient Emission Test (HKTET). Conversely, 558 vehicle licenses were withdrawn.

Also, a pilot repair initiative was performed on 600 LPG taxis, the result of which was a dramatic reduction of emission rates from 63% to 7%.

Overall, the research team discovered that Hong Kong’s remote sensing enforcement program managed to help achieve a substantial and persistent drop in the degree of toxic chemicals in the atmosphere.

They reckon that total carbon monoxide, nitric oxide and hydrocarbons can be lowered by 47%, 39% and 22% correspondingly when all highly polluting vehicles are repaired.

This is the first study of its kind to link on-site measurement of vehicle emissions with follow-up actions for repair of the high polluting vehicles. It provides insights for policymakers not just on monitoring but also implementing enforcement programs.

Yuhan Huang, Postdoctoral Research Fellow, University of Technology Sydney

References and Further Reading

Huang Y., et al., (2022). Rapid detection of high-emitting vehicles by on-road remote sensing technology improves urban air quality. Science Advances, [online] Vol. 8 no. 5. Available at:

University of Technology Sydney (2022) Remote sensing technology reduces urban air pollution. [online] Available at:

ICCT (2019) New study quantifies the global health impacts of vehicle exhaust. [online] Available at:

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William Alldred

Written by

William Alldred

William Alldred is a freelance B2B writer with a bachelor’s degree in Physics from Imperial College, London. William is a firm believer in the power of science and technology to transform society. He’s committed to distilling complex ideas into compelling narratives. Williams’s interests include Particle & Quantum Physics, Quantum Computing, Blockchain Computing, Digital Transformation and Fintech.


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