Prepared by: Dr. Mohd Rashidi Abdull Manap AMRSC, FSSM | 

Haze is not just an aesthetic nuisance or a visibility issue. It is a chemically complex mixture of pollutants suspended in the gas phase. Primarily associated with fine particulate matter (PM₂.₅), haze contains a blend of organic compounds, inorganic ions (like sulfate and nitrate), metallic trace elements (such as lead, zinc, and iron), and carbonaceous particles including black and brown carbon. These pollutants arise from both primary sources (e.g., vehicle exhaust, industrial emissions, biomass burning) and secondary formation processes where gases transform into particles in the atmosphere.

Image taken from a rooftop building in Kuala Lumpur, August 2025. (Credit: Mr. Muhammad Hafiz Fitri)

To combat this growing environmental and public health challenge, scientists and environmental agencies are turning to spectroscopy, a suite of advanced optical techniques for real-time, high-resolution tracking of haze-related pollutants.

 

Why Spectroscopy Works for Haze Monitoring?

1. Fast, Non-Invasive Detection
   Techniques such as Differential Optical Absorption Spectroscopy (DOAS) and Fourier Transform Infrared Spectroscopy (FTIR) can remotely detect pollutants like NO₂, SO₂, and O₃ by measuring their unique light absorption patterns without the need for physical sampling.
2. High Sensitivity for Trace Gases
   Tools like Cavity Ring-Down Spectroscopy (CRDS) and Tunable Diode Laser Absorption Spectroscopy (TDLAS) can detect even tiny concentrations of pollutants (down to parts per billion), making them ideal for early haze warnings and continuous surveillance.
3. Spatial and Temporal Mapping
   With advanced setups, scientists can track pollution plumes across vast urban and industrial landscapes, observing how pollutant levels change in both time and space.

 

Haze isn’t always just gray or white. It can shift in color from bluish, yellowish, to even reddish depending on a combination of atmospheric conditions, light interactions, and pollutant composition. These color variations provide valuable clues about what’s happening in the air.

1. Environmental Composition

• Dust, sea salt, and chemical aerosols in the atmosphere scatter sunlight differently depending on their size and chemical makeup.
• For example, sea salt particles can give a bluish hue, while industrial emissions rich in nitrogen oxides may result in a brownish or yellowish haze. 

2. Aerosol Concentration

• The more fine particles (PM₂.₅ and PM₁₀) in the air, the more sunlight is scattered and absorbed.
• Studies show that sky color changes rapidly with small increases in aerosol concentration but plateaus at high concentrations. This is known as a logarithmic-like color response.

 

Real-World Applications

• Early Warning Systems: When combined with meteorological and traffic data, spectroscopic monitoring can trigger public health alerts or prompt temporary traffic restrictions during severe haze events.
• Policy and Regulation: Real-time emissions data help authorities enforce air quality regulations and trace illegal pollution sources.
• Atmospheric Chemistry Research: Spectroscopic measurements are essential for understanding complex chemical reactions in the air such as the formation of secondary aerosols and the role of humidity in particle growth.

 

Haze is more than just “dirty air.” It’s a dynamic and reactive chemical recipe that poses serious health and environmental risks. In contrast, spectroscopy offers a scalable, sensitive, and real-time solution for tracking and understanding haze, enabling scientists and policymakers to respond swiftly and effectively. As cities around the world grapple with worsening air pollution, spectroscopy will play a critical role in monitoring and managing our atmosphere.

 

Dr Mohd Rashidi Abdull Manap AMRSC, FSSM is a faculty member at the Department of Chemistry, Universiti Putra Malaysia (UPM). In addition, he is a Visiting Research Fellow at Lund University, Sweden, currently based at BMC - Biomedicinskt Centrum.

Date of Input: 25/07/2025 | Updated: 25/07/2025 | hidayahsaleh