Hourly Mapping of the Layer Height of Thick Smoke Plumes Over the Western U.S. in 2020 Severe Fire Season

Zhendong Lu,Jun Wang,Shobha Kondragunta,Omar Torres,Eric M Wilcox,Xiaoguang Xu,Jing Zeng,Xi Chen

doi:10.3389/frsen.2021.766628

Abstract

A series of huge smoke plume events from the largest wildfire season recorded in California’s modern history has occurred in 2020. Here, a research algorithm was modified to retrieve the aerosol optical centroid height (AOCH) and aerosol optical depth (AOD) from Earth Polychromatic Imaging Camera (EPIC) measurements. The research focus is to gain insights of the algorithm’s feasibility in heavy smoke conditions to study the diurnal variation of AOCH; this is only made possible via EPIC due to its unique position at Lagrange-1 point and its equipment of O2 B-band at which the vegetated surface reflectance is low. Vicarious calibration is applied to the EPIC 443, 680 and 688 nm channels based on the Tropospheric Monitoring Instrument (TROPOMI) observation. This new calibration leads to a better agreement of AOCH values between EPIC retrievals and the counterparts derived from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol extinction vertical profile. The hourly variation of AOCH up to 0.45 km on September 7 is shown to have important implications for estimating hourly change of surface PM2.5, although more quantitative studies are needed in the future.

Highlights

The vertical distribution of smoke aerosols from wildfires has several important effects on the weather, climate and air quality
This study applied vicarious calibration to EPIC measurements based on the TROPOMI level 1B data to retrieve the smoke aerosol optical centroid heights for the 2020 California fire events
The vicarious calibration leads to important improvement of the EPIC AOCH retrieval

Summary

Introduction

The vertical distribution of smoke aerosols from wildfires has several important effects on the weather, climate and air quality. Via absorbing and scattering of radiation, the altitude of smoke plumes can influence how aerosols alter the thermodynamic structure of atmosphere in the vertical dimension, affecting the formation and lifecycle of clouds (Wilcox, 2012). The smoke aerosols can be entrained into the clouds and serve as condensation nuclei for cloud formation, thereby affecting the microphysics and radiative effect of clouds. This process highly depends on the vertical distance between aerosol layer and clouds (Rajapakshe et al, 2017). The characterization of smoke vertical distribution is very important for the retrieval of aerosol

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