Interannual variability and trends of combustion aerosol and dust in major continental outflows revealed by MODIS retrievals and CAM5 simulations during 2003-2017.

Hongbin Yu,Yang Yang,Lorraine A Remer,Robert C Levy,Yingxi Shi,Tianle Yuan,Qian Tan,Mian Chin,Steven J Smith,Hailong Wang

doi:10.5194/acp-20-139-2020

Abstract

Emissions and long-range transport of mineral dust and combustion-related aerosol from burning fossil fuels and biomass vary from year to year, driven by the evolution of the economy and changes in meteorological conditions and environmental regulations. This study offers both satellite and model perspectives on the interannual variability and possible trends of combustion aerosol and dust in major continental outflow regions over the past 15 years (2003–2017). The decade-long record of aerosol optical depth (AOD, denoted as τ), separately for combustion aerosol (τc) and dust (τd), over global oceans is derived from the Collection 6 aerosol products of the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard both Terra and Aqua. These MODIS Aqua datasets, complemented by aerosol source-tagged simulations using the Community Atmospheric Model version 5 (CAM5), are then analyzed to understand the interannual variability and potential trends of τc and τd in the major continental outflows. Both MODIS and CAM5 consistently yield a similar decreasing trend of −0.017 to −0.020 per decade for τc over the North Atlantic Ocean and the Mediterranean Sea that is attributable to reduced emissions from North America and Europe, respectively. On the contrary, both MODIS and CAM5 display an increasing trend of +0.017 to +0.036 per decade for τc over the tropical Indian Ocean, the Bay of Bengal, and the Arabian Sea, which reflects the influence of increased anthropogenic emissions from South Asia and the Middle East in the last 2 decades. Over the northwestern Pacific Ocean, which is often affected by East Asian emissions of pollution and dust, the MODIS retrievals show a decreasing trend of −0.021 per decade for τc and −0.012 per decade for τd, which is, however, not reproduced by the CAM5 model. In other outflow regions strongly influenced by biomass burning smoke or dust, both MODIS retrievals and CAM5 simulations show no statistically significant trends; the MODIS-observed interannual variability is usually larger than that of the CAM5 simulation.

Highlights

Mineral dust resulting from wind erosion in arid and semiarid regions and combustion-related aerosol from burning fossil fuels and biomass are transported at intercontinental and hemispherical scales and deposited into adjacent oceans in large amounts (Yu et al, 2013a; Uno et al, 2009)
Specific science questions we address include the following: how has industrial pollution changed on a regional basis in recent decades? How do episodic dust and biomass burning smoke vary from year to year? Are there regional trends over the past 15 years? Why does the aerosol change? Is the aerosol optical depth (AOD) trend consistent with that of aerosol emissions? We proceed to achieve the objective through a combined analysis of satellite retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument and model simulations from the Community Atmosphere Model version 5 (CAM5)
We focus on the outflow regions over water bodies because the MODIS retrievals of AOD and particle properties are more accurate over ocean than over land, and we can better separate combustion aerosol from dust

Summary

Introduction

Mineral dust resulting from wind erosion in arid and semiarid regions and combustion-related aerosol from burning fossil fuels and biomass are transported at intercontinental and hemispherical scales and deposited into adjacent oceans in large amounts (Yu et al, 2013a; Uno et al, 2009) These aerosols exert important and far-reaching impacts on a variety of aspects of the environment, including air quality and human health (Prospero, 1999; Chin et al, 2007; Anenberg et al, 2014; Tao et al, 2016), the radiation budget (Yu et al, 2006, 2012, 2013b; Song et al, 2018; Yang et al, 2017a, 2018a), cloud lifecycles and precipitation It remains a great challenge to quantify the changes in aerosol sources, long-range transport, and environmental impacts

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Results

Conclusion