Estimating the Aerosol Direct Radiative Effect Using Different Mixing State Assumptions Open Access

Abstract

Aerosols, whether produced from man-made or natural processes, can impact our climate by altering the radiative balance of the planet. The aerosol direct radiative effect is used to quantify the impact that aerosols have on the incoming and outgoing radiative fluxes of the Earth. Aerosols alter the radiative balance of the Earth by both scattering and absorbing incoming solar radiation, preventing it from warming the planet's surface. The degree to which the aerosols scatter or absorb solar radiation is based on their physical and chemical properties: their mixing state. The mixing state cannot be easily inferred from airborne data, so certain assumptions must be made in regards to the size and chemical mix of the sampled aerosol population. This study compares the direct radiative effect of airborne data using three mixing state assumptions: 1) The aerosols are of the same size and they are fully internally mixed, 2) The aerosols are of different sizes and they are fully internally mixed, and 3) The aerosols are of different sizes and they are fully externally mixed. This study attempts to quantify the difference in the direct radiative effect when these different mixing state assumptions are applied.

Table of Contents

1 Introduction 1

2 Methods 4

2.1 Direct Radiative Effect . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Mie Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.3 Radiative Transfer in Aerosol Layer (β, ω, & τ ) . . . . . . . . . . . . 8

2.3.1 Monodisperse Size Distribution . . . . . . . . . . . . . . . . . 10

2.3.2 Integration Over Observed Particle Size Distribution . . . . . 12

2.4 SARP and Instrumentation . . . . . . . . . . . . . . . . . . . . . . . 15

2.4.1 UHSAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.4.2 AMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.4.3 SP2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.4.4 TSI-3563 & PSAP . . . . . . . . . . . . . . . . . . . . . . . . 18

2.5 AERONET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2.6 Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.6.1 Flights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3 Results 24

3.1 SSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.2 AOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.3 DRE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4 Analysis 36

4.1 The Impact of the Mixing State . . . . . . . . . . . . . . . . . . . . . 36

4.2 Aerosol Peak Concentrations in the Southern California Basin . . . . 38

4.3 Single Scattering Albedo . . . . . . . . . . . . . . . . . . . . . . . . . 40

4.4 What Impacts the Direct Radiative Effect? . . . . . . . . . . . . . . . 42

4.4.1 Single Scattering Albedo . . . . . . . . . . . . . . . . . . . . . 42

4.4.2 Optical Thickness . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.4.3 Surface Albedo . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.5 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

4.5.1 Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . 46

4.5.2 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

5 Conclusion 50

5.1 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

6 Appendix 53

6.1 Code Processing Diagrams . . . . . . . . . . . . . . . . . . . . . . . . 53

Bibliography 56

About this Honors Thesis

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School	Emory College
Department	Environmental Studies
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Atmospheric Chemistry Physics, General Atmospheric Sciences
Keyword	Climate Direct Radiative Effect Aerosols
Committee Chair / Thesis Advisor	Alexander Avramov, Emory University
Committee Members	Eri Saikawa, Emory University Justin Burton, Emory University

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