title: Radiative absorption enhancements due to the mixing state of atmospheric black carbon.
abstract: Atmospheric black carbon (BC) warms Earth's climate, and its reduction has been targeted for near-term climate change mitigation. Models that include forcing by BC assume internal mixing with non-BC aerosol components that enhance BC absorption, often by a factor of ~2; such model estimates have yet to be clearly validated through atmospheric observations. Here, direct in situ measurements of BC absorption enhancements (E(abs)) and mixing state are reported for two California regions. The observed E(abs) is small-6% on average at 532 nm-and increases weakly with photochemical aging. The E(abs) is less than predicted from observationally constrained theoretical calculations, suggesting that many climate models may overestimate warming by BC. These ambient observations stand in contrast to laboratory measurements that show substantial E(abs) for BC are possible.
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Davis, CA 95616, USA. cdcappa@ucdavis.edu
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Cappa
authors.forename: Timothy B
authors.initials: TB
authors.lastname: Onasch
authors.forename: Paola
authors.initials: P
authors.lastname: Massoli
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Worsnop
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Bates
authors.forename: Eben S
authors.initials: ES
authors.lastname: Cross
authors.forename: Paul
authors.initials: P
authors.lastname: Davidovits
authors.forename: Jani
authors.initials: J
authors.lastname: Hakala
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Hayden
authors.forename: B Tom
authors.initials: BT
authors.lastname: Jobson
authors.forename: Katheryn R
authors.initials: KR
authors.lastname: Kolesar
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Lack
authors.forename: Brian M
authors.initials: BM
authors.lastname: Lerner
authors.forename: Shao-Meng
authors.initials: SM
authors.lastname: Li
authors.forename: Daniel
authors.initials: D
authors.lastname: Mellon
authors.forename: Ibraheem
authors.initials: I
authors.lastname: Nuaaman
authors.forename: Jason S
authors.initials: JS
authors.lastname: Olfert
authors.forename: Tuukka
authors.initials: T
authors.lastname: Petäjä
authors.forename: Patricia K
authors.initials: PK
authors.lastname: Quinn
authors.forename: Chen
authors.initials: C
authors.lastname: Song
authors.forename: R
authors.initials: R
authors.lastname: Subramanian
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Williams
authors.forename: Rahul A
authors.initials: RA
authors.lastname: Zaveri
mesh_terms: D000327:Adsorption; D001272:Atmosphere / Q000737:chemistry*; D002140:California; D002244:Carbon / Q000032:analysis / Q000737:chemistry*; D057232:Global Warming; D008027:Light; D010316:Particle Size; D055668:Photochemical Processes; D053260:Soot / Q000032:analysis / Q000737:chemistry*
chemical_list: D053260:Soot; D002244:Carbon