Planetary Boundary Layer

The planetary boundary layer (PBL), also called the atmospheric boundary layer, is the region of the lower troposphere where Earth’s surface strongly influences temperature, moisture, and wind through the turbulent transfer of air mass. The PBL acts like a cap, trapping pollutants in the atmospheric layer nearest the Earth’s surface. Understanding its characteristics is critical for effective modeling of air quality.

Discoveries that matter

PBL height is a key input in air quality models because the PBL defines the mixing height of air pollutants in the lowest layer of the atmosphere. The PBL responds to surface activity within an hour or less, making it very dynamic and difficult to measure.

The PBL can grow to a height of thousands of meters during the day and collapse to 100 m or less at nighttime, varying spatially based on micro-climate.

Real-time vertical profile data provides accurate PBL height, greatly improving the accuracy of air quality models.

The Micro Pulse LiDAR (MPL) scanning system provides the most accurate information about the PBL by detecting and measuring the size and type of particles in the atmosphere in a vertical swath up to 15 kilometers high. By studying the movement of the emissions plume in relation to the PBL, wind direction and other factors, pollution sources are more easily identified.

By NikNaks – Own work based on: also:, CC BY-SA 3.0,

MPL provides real time information about the PBL over time. In this data set, storms at the beginning of the data set give way leading to a low PBL height. The PBL rises as the new days begins and hangs out around 2km for the next two days. Clear skies over this period after the storm.

"Historically, PBL soundings have been taken at specific rural locations only twice a day, whereas the high temporal resolution of the MiniMPL provides a complete 24-hour record and reflects conditions in situ."

-Yanina Barrera, Harvard University

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MiniMPL Mini Micro Pulse LiDAR

A small form factor, low-power, elastic backscatter lidar designed to determine the altitude of clouds and to detect atmospheric aerosols.

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MPL Micro Pulse LiDAR

An elastic backscatter LiDAR designed for long-term, autonomous aerosol and cloud monitoring.

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