Figure 4 shows that enhancement factors for
most other atmospheric aerosols lie between
two and three, typically reaching their max-
imum for PM2.5 particles (r 0 < 1.25mm). The
results for water (blue trace in Fig. 4B) show
that light-enhancement factors around two
are also expected in cloud droplets, certainly
up to sizes of many micrometers. Accounting
foretotin clouds could improve predictions
of radical formation in clouds ( 38 ) and of the
formation of aqueous SOAs ( 39 ).
With typical light-enhancement factors of
two to three attained by most atmospheric
particles, photochemical reactions in these
particles are generally expected to be accel-
erated on average by the same factor. Ac-
counting foretotin SOAs should improve the
prediction of the SOA evolution ( 40 ). This
might explain the mismatch between obser-
vations and model predictions of SOA mass
loss by a factor of two to three, as reported
by Hodzicet al.( 41 ). They used a chemical
model to simulate the evolution of submicron
a-pinene SOA particles under aging condi-
tions and applied their results to a global
chemistry model; however, OC effects were
not considered. Given that the authors found
photolysis in the particle phase to be a domi-
nant degradation pathway of SOAs, it appears
plausible that the neglect of the acceleration of
photochemical reactions by light-enhancement
effects in the aerosol particles could contribute
to the reported discrepancy between model
and observation.
Our study provides evidence that light-
enhancement effects in typical aerosol parti-
cles are more important for photochemical
reactions than previously anticipated. For most
atmospheric aerosol particles, we argue that
an acceleration of photochemical reactions
compared with bulk reactions will occur. In
view of its prevalence, atmospheric aerosol
and cloud models should now account for this
phenomenon to improve global chemistry
models and climate predictions.REFERENCES AND NOTES- U. Pöschl,Angew. Chem. Int. Ed. 44 , 7520–7540 (2005).
- J. L. Jimenezet al.,Science 326 , 1525–1529 (2009).
- M. E. Mongeet al.,Proc. Natl. Acad. Sci. U.S.A. 109 ,
6840 – 6844 (2012). - A. Tilgner, P. Bräuer, R. Wolke, H. Herrmann,J. Atmos. Chem.
70 , 221–256 (2013). - M. Shiraiwaet al.,Proc. Natl. Acad. Sci. U.S.A. 110 ,
11746 – 11750 (2013). - A. Laskinet al.,Science 301 , 340–344 (2003).
- C. George, M. Ammann, B. D’Anna, D. J. Donaldson,
S. A. Nizkorodov,Chem. Rev. 115 , 4218–4258 (2015). - S. Canonica,Chimia 61 , 641–644 (2007).
- K. McNeill, S. Canonica,Environ. Sci. Process. Impacts 18 ,
1381 – 1399 (2016). - P. Corral Arroyoet al.,Environ. Sci. Technol. 52 , 7680– 7688
(2018). - H. Herrmannet al.,J. Atmos. Chem. 36 , 231–284 (2000).
- C. Weller, A. Tilgner, P. Bräuer, H. Herrmann,Environ. Sci. Technol.
48 , 5652–5659 (2014). - J. Douet al.,Atmos. Chem. Phys. 21 , 315–338 (2021).
- J. M. Anglada, M. T. C. Martins-Costa, J. S. Francisco,
M. F. Ruiz-López,J. Am. Chem. Soc. 142 , 16140– 16155
(2020). - K. J. Kappeset al.,J. Phys. Chem. A 125 , 1036– 1049
(2021).
16. S. Banerjee, E. Gnanamani, X. Yan, R. N. Zare,Analyst 142 ,
1399 – 1402 (2017).
17. R. M. Bain, C. J. Pulliam, R. G. Cooks,Chem. Sci. 6 , 397– 401
(2015).
18. T. Müller, A. Badu-Tawiah, R. G. Cooks,Angew. Chem. Int. Ed.
51 , 11832–11835 (2012).
19. P. Nissenson, C. J. H. Knox, B. J. Finlayson-Pitts, L. F. Phillips,
D. Dabdub,Phys. Chem. Chem. Phys. 8 , 4700– 4710
(2006).
20. D. L. Bones, L. F. Phillips,Phys. Chem. Chem. Phys. 11 ,
5392 – 5399 (2009).
21. J. W. Cremer, K. M. Thaler, C. Haisch, R. Signorell,Nat.
Commun. 7 , 10941 (2016).
22. R. Signorellet al.,Chem. Phys. Lett. 658 ,1–6 (2016).
23. Y. Zhanget al.,NPJ Clim. Atmos. Sci. 1 , 47 (2018).
24. R. Symes, R. M. Sayer, J. P. Reid,Phys. Chem. Chem. Phys. 6 ,
474 – 487 (2004).
25. M. A. Yurkin, A. G. Hoekstra,J. Quant. Spectrosc. Radiat.
Transf. 112 , 2234–2247 (2011).
26. M. Shiraiwaet al.,Nat. Commun. 8 , 15002 (2017).
27. A. Virtanenet al.,Nature 467 , 824–827 (2010).
28. P. A. Alpertet al.,Nat. Commun. 12 , 1769 (2021).
29. P. Liu, Y. Zhang, S. T. Martin,Environ. Sci. Technol. 47 ,
13594 – 13601 (2013).
30.P.F.Liuet al.,Atmos. Chem. Phys. 15 , 1435– 1446
(2015).
31. E. Dinaret al.,Faraday Discuss. 137 , 279–295 (2008).
32. M. Ebert, S. Weinbruch, P. Hoffmann, H. M. Ortner,Atmos.
Environ. 38 , 6531–6545 (2004).
33. J. Kimet al.,Aerosol Sci. Technol. 49 , 340–350 (2015).
34. E. Sarpong, D. Smith, R. Pokhrel, M. N. Fiddler, S. Bililign,
Atmosphere 11 , 62 (2020).
35. L. Biet al.,J. Geophys. Res. Atmos. 123 , 543–558 (2018).
36. G. M. Hale, M. R. Querry,Appl. Opt. 12 , 555–563 (1973).
37. J. Liet al.,Atmos. Chem. Phys. 20 , 4889–4904 (2020).
38. H. Herrmannet al.,Chem. Rev. 115 , 4259–4334 (2015).
39. B. Ervens, B. J. Turpin, R. J. Weber,Atmos. Chem. Phys. 11 ,
11069 – 11102 (2011).
40. M. Shrivastavaet al.,Rev. Geophys. 55 , 509–559 (2017).
41. A. Hodzicet al.,Atmos. Chem. Phys. 15 , 9253– 9269
(2015).
42. P. Corral Arroyoet al., Data Collection: Amplification
of light within aerosol particles accelerates in-particle
photochemistry. ETH Zürich (2022); https://doi.org/10.
3929/ethz-b-000531184.
43. G. David, Registered software:“Particle_internalintensity
enhancement_factor.py”. ETH Zürich (2022); https://doi.org/
10.5905/ethz-1007-500.
ACKNOWLEDGMENTS
We acknowledge B. Watts for support during the beamtime at the
PolLux end station of the Swiss Light Source and M. Shiraiwa
and Y. Li for sharing their global maps of SOA viscosity (fig. S7).
Funding:This project has received funding from the Swiss National
Science Foundation (project 200020_200306) and the European
Research Council (Horizon 2020 Research and Innovation
Programme grant agreement 786636). The PolLux end station was
financed by the German Ministerium für Bildung und Forschung
(BMBF) through contracts 05K16WED and 05K19WE2.Author
contributions:Conceptualization: P.C.A., R.S.; Methodology:
P.C.A., G.D., P.A.A., R.S.; Investigation: P.C.A., G.D., P.A.A., E.A.P.;
Funding acquisition: R.S.; Project administration: P.C.A., R.S.;
Supervision: R.S.; Writing–original draft: P.C.A., G.D., R.S.;
Writing–review and editing: P.C.A., G.D., R.S., E.A.P., P.A.A., M.A.
Competing interests:The authors declare no conflicts of interest.
Data and materials availability:All data that reproduce the
analyses are available in a data repository ( 42 ). A Python program
for the calculations of enhancement factors (SM section S12) is
available in a project-associated data archive repository ( 43 ).SUPPLEMENTARY MATERIALS
science.org/doi/10.1126/science.abm7915
Supplementary Text
Figs. S1 to S8
References ( 44 – 51 )
Movies S1 and S212 October 2021; accepted 14 March 2022
10.1126/science.abm7915296 15 APRIL 2022¥VOL 376 ISSUE 6590 science.orgSCIENCE
Fig. 4. OC effects in typical atmospheric aerosol particles.(A) The total light-enhancement factor,
etot(see color scale bar), for spherical particles averaged over the wavelength range of 280 to 440 nm
as a function of the particle radius (r 0 ) and the imaginary part of the refractive index (k) for constant
n= 1.5 (SM section S12). The dashed colored rectangles indicate the range of properties for different
classes of ambient aerosol particles: SOA particles (black), HULIS particles (blue), urban particles
(red), rural particles (green), soot (brown), organic biomass burning particles (purple), and sea salt
particles (white). (B)etotas a function of the particle radius for SOA material from limonene,a-pinene,
and catechol and for BrC particles. These predictions are for spherical particles using wavelength-
dependent refractive index data for the respective materials from the literature in the wavelength range of
280 to 440 nm. For the averaging over the wavelength range of 280 to 440 nm, the relative contribution of
each wavelength was weighted according to its relative intensities in sunlight (SM section S12).
RESEARCH | REPORTS