Title: Response of Surface Ultraviolet and Visible Radiation to Stratospheric SO₂ Injections

Abstract

Climate modification by stratospheric SO₂ injections, to form sulfate aerosols, may alter the spectral and angular distributions of the solar ultraviolet and visible radiation that reach the Earth’s surface, with potential consequences to environmental photobiology and photochemistry. We used modeling results from the CESM1(WACCM) stratospheric aerosol geoengineering large ensemble (GLENS) project, following the RCP8.5 emission scenario, and one geoengineering experiment with SO₂ injections in the stratosphere, designed to keep surface temperatures at 2020 levels. Zonally and monthly averaged vertical profiles of O₃, SO₂, and sulfate aerosols, at 30 N and 70 N, served as input into a radiative transfer model, to compute biologically active irradiances for DNA damage (i_DNA), UV index (UVI), photosynthetically active radiation (PAR), and two key tropospheric photodissociation coefficients (j_O1D for O₃ + hν (λ < 330 nm) → O(¹D) + O₂; and j_NO2 for NO₂ + hν (λ < 420 nm) → O(³P) + NO). We show that the geoengineering scenario is accompanied by substantial reductions in UV radiation. For example, comparing March 2080 to March 2020, i_DNA decreased by 25% to 29% in the subtropics (30 N) and by 26% to 33% in the polar regions (70 N); UVI decreased by 19% to 20% atmore » 30 N and 23% to 26% at 70 N; and j_O1D decreased by 22% to 24% at 30 N and 35% to 40% at 70 N, with comparable contributions from sulfate scattering and stratospheric O₃ recovery. Different responses were found for processes that depend on longer UV and visible wavelengths, as these are minimally affected by ozone; PAR and j_NO2 were only slightly lower (9–12%) at 30 N, but much lower at 70 N (35–40%). Similar reductions were estimated for other months (June, September, and December). Large increases in the PAR diffuse-direct ratio occurred in agreement with previous studies. Absorption by SO₂ gas had a small (~1%) effect on j_O1D, i_DNA, and UVI, and no effect on j_NO2 and PAR.« less

Authors:

Madronich, Sasha  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-0983-1313"

Tilmes, Simone ^[1]; Kravitz, Benjamin S.  ^[2];

• Search DOE PAGES for author "Kravitz, Benjamin S."
• Search DOE PAGES for ORCID "0000-0001-6318-1150"

MacMartin, Douglas  ^[3];

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• Search DOE PAGES for ORCID "0000-0003-1987-9417"

Richter, Jadwiga ^[1]

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+ Show Author Affiliations

1. National Center for Atmospheric Research, Boulder, CO (United States)
2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
3. Cornell Univ., Ithaca, NY (United States)

Publication Date:

Wed Nov 07 00:00:00 EST 2018

Research Org.:

Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1507988

Report Number(s):

PNNL-SA-138064
Journal ID: ISSN 2073-4433; ATMOCZ

Grant/Contract Number:  

AC05-76RL01830

Resource Type:

Accepted Manuscript

Journal Name:

Atmosphere (Basel)

Additional Journal Information:

Journal Name: Atmosphere (Basel); Journal Volume: 9; Journal Issue: 11; Journal ID: ISSN 2073-4433

Publisher:

MDPI

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; 42 ENGINEERING; geoengineering; sulfate aerosols; stratosphere; stratospheric ozone; ultraviolet radiation; erythemal radiation; photolysis coefficients; photosynthetically active radiation (PAR); direct-diffuse ratio