How Do Height and Temperature Affect PM2.5?

Created By RISC | 8 months ago

Last modified date : 8 months ago

Many people believe that the higher you go, the cooler you get. But this isn't always the case. RISC is here to help explain.​

We experience cooler temperatures when we climb a mountain. The temperature will drop by about 9.8°C for every 1 km of height. To make things easier, we'll refer to this as "Layer 1" or the "Urban Boundary Layer".​

But the cold gradually fades. At a specific elevation, the temperature rises with altitude, known as "Layer 2" or "Inversion Layer". This layer is typically 1-2 km high but can be lower at times. After this level, the temperature will fall as the height rises, until we leave the earth's atmosphere. The "Inversion Layer" acts as a cone-shaped cover, preventing various particles from dispersing away from the "Urban Boundary Layer."​

Depending on the height of the "Inversion Layer" above ground level, exhaust smoke from cars and particles from various sources will float higher and become diluted with the air. If it is higher, it will improve air ventilation by reducing pollution concentrations in the atmosphere. But if the "Inversion Layer" is low, air pollution will be concentrated and unable to float up or be diluted with air, resulting in inadequate air ventilation.​

The height of the "Inversion Layer" depends on the time of day and season. During the day, when the sun's heat reaches the atmosphere, the air expands and rises. During the night, as the air cools to a high density, the "Inversion Layer" presses down and remains lower. During the winter, as air pressure rises, the "Urban Boundary Layer" is thinner than during the wet and hot seasons. As a result, many places experience higher PM2.5 concentration difficulties during the winter, both day and night, compared with other seasons.​

Particle problems in many areas, particularly Bangkok, are caused by both human and natural forces during periods of inadequate ventilation. Understanding natural particle formation can help us create preventive technologies and manage specific human activities during periods of low natural ventilation, another critical issue for finding solutions and adapting to bad air quality.​

Story by Dr. Parkin Maskulrath, Lecturer, Department of Environmental Science, Faculty of Environment, Kasetsart University and Thanawat Jinjaruk, Senior Researcher, Environment Division and Urban Environmental & Biodiversity Engineer, RISC​