A Multi Linear Regression Model to Derive Dust PM10 in the Sahel Using AERONET Aerosol Optical Depth and CALIOP Aerosol Layer Products

Jean-François Léon,Nadège Martiny,Sébastien Merlet

doi:10.3390/rs12183099

Abstract

Due to a limited number of monitoring stations in Western Africa, the impact of mineral dust on PM10 surface concentrations is still poorly known. We propose a new method to retrieve PM10 dust surface concentrations from sun photometer aerosol optical depth (AOD) and CALIPSO/CALIOP Level 2 aerosol layer products. The method is based on a multi linear regression model that is trained using co-located PM10, AERONET and CALIOP observations at 3 different locations in the Sahel. In addition to the sun photometer AOD, the regression model uses the CALIOP-derived base and top altitude of the lowermost dust layer, its AOD, the columnar total and columnar dust AOD. Due to the low revisit period of the CALIPSO satellite, the monthly mean annual cycles of the parameters are used as predictor variables rather than instantaneous observations. The regression model improves the correlation coefficient between monthly mean PM10 and AOD from 0.15 (AERONET AOD only) to 0.75 (AERONET AOD and CALIOP parameters). The respective high and low PM10 concentration during the winter dry season and summer season are well produced. Days with surface PM10 above 100 μg/m3 are better identified when using the CALIOP parameters in the multi linear regression model. The number of true positives (actual and predicted concentrations above the threshold) is increased and leads to an improvement in the classification sensitivity (recall) by a factor 1.8. Our methodology can be extrapolated to the whole Sahel area provided that satellite derived AOD maps are used in order to create a new dataset on population exposure to dust events in this area.

Highlights

Aeolian mineral dust is a major component of the aerosol load in the atmosphere of our planet
We introduce the seasonal variability by using the monthly mean annual cycle of Aerosol Robotic Network (AERONET) aerosol optical depth (AOD) and CALIOP parametes
The CALIOP layer aerosol layer products have been used to improve the statistical relationship between AOD and surface PM10 at three stations located in the Sahel over a period of 10 years

Summary

Introduction

Aeolian mineral dust is a major component of the aerosol load in the atmosphere of our planet. Desert dust is transported over thousands of kilometers and reaches environments far from emission areas. Northern Africa is the largest source of suspended mineral dust in the world with emission of 400 to 2200 Tgr/yr [4]. During the dry season from October to April, the Sahel is under the influence of the northeasterly Harmattan wind [9] bringing dust to populated areas of western Africa. Dust impacts the wellness and health of human beings because of its respirable fraction [13]. Dust events are suspected to play a role in the meningitis outbreaks occurring in the so-called “Meningitis belt” in Northern Africa [14] during the dry season [15,16,17,18]. The scarcity of in situ observations of dust surface concentrations in Northern Africa is a limitating factor for a better assessment of the dust impact on health

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Conclusion