Researchers use Micro Pulse LiDAR to study the effects of lockdowns imposed by the COVID-19 pandemic on vertically resolved aerosol profiles

In an innovative preliminary study, Dr. Simone Lolli, who is affiliated with CNR-IMAA, Istituto di Metodologie per l’Analisi Ambientale (CNR) in Tito Scalo, Italy and NASA Goddard Space Flight Center in Maryland, USA (GSFC), used Micro Pulse Lidar (MPL) observations to help investigate the effect of COVID-19 lockdowns on local climate. Dr. Lolli chose to contrast observations from the GSFC MPL with the National University of Singapore unit. Two sites with sufficient baseline data, where imposed lockdown measures varied in strictness.

High aerosol levels in the local atmosphere from pollution have a profound negative effect on quality of life. Prolonged exposure to ambient PM2.5 has been likened to smoking 25 cigarettes a day. The influence of aerosols on climate and radiative balance is varied, and thus less well characterized. Depending on their type, aerosols can change the reflectivity of clouds and even inhibit or enhance their formation by changing the quantity and size of water droplets. High concentrations of radiation absorbing carbon black will lead to warming; in contrast reflective sulphates will stop radiation reaching the surface, leading to cooling.

To investigate this, observations from the global Micro Pulse Lidar Network were used. Operating since 1998, the Micro Pulse Lidar Network (MPLNET) is a federated network of continuously operating MPL systems made up of NASA owned and operated sites and those administered by partner organizations. Thus, MPLNET offers a large historical record of observations that can be used to create a baseline aerosol burden. In this way, averaged aerosol backscatter coefficient baselines under ‘normal’ conditions were constructed that could be compared to averaged profiles during COVID-19 pandemic lockdown measures. Extinction profiles calculated from the backscatter could then be fed into the Fu-Liou-Gu radiative transfer model to evaluate the relative effect of aerosols on the system atmosphere.

At GSFC the baseline was computed using continuous observations from March-April-May 2011 to 2019 (shown in blue on the left hand graphic). During lockdown (shown in red on the left hand graphic) the aerosol backscatter was clearly lower, except for an aerosol peak at 2.5km, meaning less aerosol burden throughout the profile. In turn, Fu-Liou-Gu showed that less energy reached the surface and the whole atmosphere was cooled by 4.29 W/m2. Further verification by heating rate difference showed that the atmospheric column was generally cooled with respect to 9 years of baselined data, with a warming peak at 2.5km.

At the NUS site, the baseline was constructed from only one-year of observations. However, the change was still much more noticeable. Lockdown measures were stricter, and this translated to a greater difference between the backscatter profiles during this time (red in the right hand graphic) and the baseline (blue in right hand graphic). This impressive aerosol burden decrease caused a cooling of 44.64 W/m2 from the Fu-Liou-Gu model. Heating rate differences again confirming this result.

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