The climate effects of ultrafine particles: uncertainties and future perspectives

Abstract

Ultrafine particles (UFPs), defined as aerosols smaller than 100 nm, are numerically dominant in the atmosphere and play a crucial role in the production of cloud condensation nuclei (CCN). They arise from both new particle formation (NPF) and subsequent growth, as well as from primary emissions such as combustion sources. Despite contributing negligibly to particulate mass, they have disproportionate effects on cloud microphysics and radiative forcing, making them important yet highly uncertain components of the climate system. Current knowledge of how UFPs influence climate points to two primary mechanisms: direct radiative effects, primarily through absorption by black carbon (BC)-containing UFPs, and indirect effects, through their contribution to CCN and subsequent modification of cloud properties. However, substantial knowledge gaps remain. Observations are limited by the low sensitivity of current instrumentation and satellite retrievals, leading to systematic underestimation of UFP abundance and uncertainties in constraining their optical properties. Moreover, large discrepancies persist between observations and model simulations of NPF survival and CCN activation, compounded by the coarse resolution and simplified parameterizations of global models. This perspective emphasizes the need for coordinated multiplatform observations, mechanistic process studies, and the development of cross-scale modeling frameworks. Addressing these challenges will advance the quantitative understanding of UFP-cloud-climate interactions and provide more robust assessments of their role in anthropogenic climate forcing.

Graphical abstract

Keywords

Ultrafine particles (UFPs) / New particle formation (NPF) / Cloud condensation nuclei (CCN) / Aerosol-cloud interactions / Radiative forcing uncertainty

Highlight

	● Ultrafine particles (UFPs) are negligible in mass but major in climate impact.
	● UFPs direct radiative effects arise mainly from black carbon absorption.
	● UFPs indirect effects via NPF and CCN are critical but uncertain.
	● Coordinated observations and cross-scale modeling are key to reduce uncertainties.

References

[1] Albrecht B A . (1989). Aerosols, cloud microphysics, and fractional cloudiness. Science, 245(4923): 1227–1230

[2] Andreae M O . (2007). Aerosols before pollution. Science, 315(5808): 50–51

[3] Anttila T , Vaattovaara P , Komppula M , Hyvärinen A P , Lihavainen H , Kerminen V M , Laaksonen A . (2009). Size-dependent activation of aerosols into cloud droplets at a subarctic background site during the second Pallas Cloud Experiment (2nd PaCE): method development and data evaluation. Atmospheric Chemistry and Physics, 9(14): 4841–4854

[4] Bellouin N , Quaas J , Gryspeerdt E , Kinne S , Stier P , Watson-Parris D , Boucher O , Carslaw K S , Christensen M , Daniau A L . et al. (2020). Bounding global aerosol radiative forcing of climate change. Reviews of Geophysics, 58(1): e2019RG000660

[5] Blichner S M , Sporre M K , Berntsen T K . (2021). Reduced effective radiative forcing from cloud–aerosol interactions (ERF_aci) with improved treatment of early aerosol growth in an Earth system model. Atmospheric Chemistry and Physics, 21(23): 17243–17265

[6] Bond T C , Doherty S J , Fahey D W , Forster P M , Berntsen T , DeAngelo B J , Flanner M G , Ghan S , Kärcher B , Koch D . et al. (2013). Bounding the role of black carbon in the climate system: a scientific assessment. Journal of Geophysical Research: Atmospheres, 118(11): 5380–5552

[7] Brock C AWashenfelder R ATrainer MRyerson T BWilson J CReeves J MHuey L GHolloway J SParrish D DHübler G, et al. (2002). Particle growth in the plumes of coal-fired power plants. Journal of Geophysical Research: Atmospheres, 107(D12): AAC 9–1-AAC 9–1

[8] Cappa C D , Onasch T B , Massoli P , Worsnop D R , Bates T S , Cross E S , Davidovits P , Hakala J , Hayden K L , Jobson B T . et al. (2012). Radiative absorption enhancements due to the mixing state of atmospheric black carbon. Science, 337(6100): 1078–1081

[9] Cass G R , Hughes L A , Bhave P , Kleeman M J , Allen J O , Salmon L G . (2000). The chemical composition of atmospheric ultrafine particles. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 358(1775): 2581–2592

[10] Corral A F , Choi Y , Crosbie E , Dadashazar H , DiGangi J P , Diskin G S , Fenn M , Harper D B , Kirschler S , Liu H Y . et al. (2022). Cold air outbreaks promote new particle formation off the US East coast. Geophysical Research Letters, 49(5): e2021GL096073

[11] Crippa P , Castruccio S , Pryor S C . (2017). Forecasting ultrafine particle concentrations from satellite and in situ observations. Journal of Geophysical Research: Atmospheres, 122(3): 1828–1837

[12] Crippa P , Spracklen D , Pryor S C . (2013). Satellite-derived estimates of ultrafine particle concentrations over eastern North America. Journal of Geophysical Research: Atmospheres, 118(17): 9968–9981

[13] (). . ,

[14] Dusek U , Frank G P , Hildebrandt L , Curtius J , Schneider J , Walter S , Chand D , Drewnick F , Hings S , Jung D . et al. (2006). Size matters more than chemistry for cloud-nucleating ability of aerosol particles. Science, 312(5778): 1375–1378

[15] Ehn M , Thornton J A , Kleist E , Sipilä M , Junninen H , Pullinen I , Springer M , Rubach F , Tillmann R , Lee B . et al. (2014). A large source of low-volatility secondary organic aerosol. Nature, 506(7489): 476–479

[16] Fan J W , Rosenfeld D , Zhang Y W , Giangrande S E , Li Z Q , Machado L A T , Martin S T , Yang Y , Wang J , Artaxo P . et al. (2018). Substantial convection and precipitation enhancements by ultrafine aerosol particles. Science, 359(6374): 411–418

[17] Fierce L , Onasch T B , Cappa C D , Mazzoleni C , China S , Bhandari J , Davidovits P , Al Fischer D , Helgestad T , Lambe A T . et al. (2020). Radiative absorption enhancements by black carbon controlled by particle-to-particle heterogeneity in composition. Proceedings of the National Academy of Sciences of the United States of America, 117(10): 5196–5203

[18] Gordon H , Kirkby J , Baltensperger U , Bianchi F , Breitenlechner M , Curtius J , Dias A , Dommen J , Donahue N M , Dunne E M . et al. (2017). Causes and importance of new particle formation in the present-day and preindustrial atmospheres. Journal of Geophysical Research: Atmospheres, 122(16): 8739–8760

[19] Gordon H , Sengupta K , Rap A , Duplissy J , Frege C , Williamson C , Heinritzi M , Simon M , Yan C , Almeida J . et al. (2016). Reduced anthropogenic aerosol radiative forcing caused by biogenic new particle formation. Proceedings of the National Academy of Sciences of the United States of America, 113(43): 12053–12058

[20] Guo S , Hu M , Peng J F , Wu Z J , Zamora M L , Shang D J , Du Z F , Zheng J , Fang X , Tang R Z . et al. (2020). Remarkable nucleation and growth of ultrafine particles from vehicular exhaust. Proceedings of the National Academy of Sciences of the United States of America, 117(7): 3427–3432

[21] Holmes N S . (2007). A review of particle formation events and growth in the atmosphere in the various environments and discussion of mechanistic implications. Atmospheric Environ-ment, 41(10): 2183–2201

[22] Huber E , Frost M . (1998). Light scattering by small particles. Journal of Water Supply: Research and Technology-AQUA, 47(2): 87–94

[23] Kahn R A , Andrews E , Brock C A , Chin M , Feingold G , Gettelman A , Levy R C , Murphy D M , Nenes A , Pierce J R . et al. (2023). Reducing aerosol forcing uncertainty by combining models with satellite and within-the-atmosphere observations: a three-way street. Reviews of Geophysics, 61(2): e2022RG000796

[24] Kerminen V M , Chen X M , Vakkari V , Petäjä T , Kulmala M , Bianchi F . (2018). Atmospheric new particle formation and growth: review of field observations. Environmental Research Letters, 13(10): 103003

[25] Khain A P , Beheng K D , Heymsfield A , Korolev A , Krichak S O , Levin Z , Pinsky M , Phillips V , Prabhakaran T , Teller A . et al. (2015). Representation of microphysical processes in cloud‐resolving models: spectral (bin) microphysics versus bulk parameterization. Reviews of Geophysics, 53(2): 247–322

[26] Kliengchuay W , Suwanmanee S , Worakhunpiset S , Tawatsupa B , Laor P , Siriratruengsuk W , Kawichai S , Phosri A , Kingkaew S , Sahanavin N . et al. (2025). Climate change and its impact on environmental health: a narrative review of tropical countries. Frontiers of Environmental Science & Engineering, 19(5): 59

[27] Kohl M , Lelieveld J , Chowdhury S , Ehrhart S , Sharma D , Cheng Y F , Tripathi S N , Sebastian M , Pandithurai G , Wang H L . et al. (2023). Numerical simulation and evaluation of global ultrafine particle concentrations at the Earth’s surface. Atmospheric Chemistry and Physics, 23(20): 13191–13215

[28] Köhler H . (1936). The nucleus in and the growth of hygroscopic droplets. Transactions of the Faraday Society, 32: 1152–1161

[29] Kuang C , McMurry P H , McCormick A V . (2009). Determination of cloud condensation nuclei production from measured new particle formation events. Geophysical Research Letters, 36(9): L09822

[30] Kulmala M , Kontkanen J , Junninen H , Lehtipalo K , Manninen H E , Nieminen T , Petäjä T , Sipilä M , Schobesberger S , Rantala P . et al. (2013). Direct observations of atmospheric aerosol nucleation. Science, 339(6122): 943–946

[31] Kumar P , Morawska L , Birmili W , Paasonen P , Hu M , Kulmala M , Harrison R M , Norford L , Britter R . (2014). Ultrafine particles in cities. Environment International, 66: 1–10

[32] Lee S H , Gordon H , Yu H , Lehtipalo K , Haley R , Li Y X , Zhang R Y . (2019). New particle formation in the atmosphere: from molecular clusters to global climate. Journal of Geophysical Research: Atmospheres, 124(13): 7098–7146

[33] Lei T , Xiang W , Zhao B , Hou C Y , Ge M F , Wang W G . (2024). Advances in analysis of atmospheric ultrafine particles and application in air quality, climate, and health research. Science of the Total Environment, 949: 175045

[34] Li C X , McMurry P H . (2018). Errors in nanoparticle growth rates inferred from measurements in chemically reacting aerosol systems. Atmospheric Chemistry and Physics, 18(12): 8979–8993

[35] Liu D T , Whitehead J , Alfarra M R , Reyes-Villegas E , Spracklen D V , Reddington C L , Kong S F , Williams P I , Ting Y C , Haslett S . et al. (2017). Black-carbon absorption enhancement in the atmosphere determined by particle mixing state. Nature Geoscience, 10(3): 184–188

[36] Ma N , Zhao C S , Tao J C , Wu Z J , Kecorius S , Wang Z B , Größ J , Liu H J , Bian Y X , Kuang Y . et al. (2016). Variation of CCN activity during new particle formation events in the North China Plain. Atmospheric Chemistry and Physics, 16(13): 8593–8607

[37] Makkonen R , Asmi A , Kerminen V M , Boy M , Arneth A , Hari P , Kulmala M . (2012). Air pollution control and decreasing new particle formation lead to strong climate warming. Atmospheric Chemistry and Physics, 12(3): 1515–1524

[38] Molnár A , Mészáros E . (2001). On the relation between the size and chemical composition of aerosol particles and their optical properties. Atmospheric Environment, 35(30): 5053–5058

[39] Moosmüller H , Arnott W P . (2009). Particle optics in the Rayleigh regime. Journal of the Air & Waste Management Association, 59(9): 1028–1031

[40] Peng J F , Hu M , Guo S , Du Z F , Zheng J , Shang D J , Levy Zamora M , Zeng L M , Shao M , Wu Y S . et al. (2016). Markedly enhanced absorption and direct radiative forcing of black carbon under polluted urban environments. Proceedings of the National Academy of Sciences of the United States of America, 113(16): 4266–4271

[41] Peters K , Stier P , Quaas J , Graßl H . (2012). Aerosol indirect effects from shipping emissions: sensitivity studies with the global aerosol-climate model ECHAM-HAM. Atmospheric Chemistry and Physics, 12(13): 5985–6007

[42] (). . ,

[43] Pierce J R , Adams P J . (2007). Efficiency of cloud condensation nuclei formation from ultrafine particles. Atmospheric Chemistry and Physics, 7(5): 1367–1379

[44] Pierce J R , Adams P J . (2009). Uncertainty in global CCN concentrations from uncertain aerosol nucleation and primary emission rates. Atmospheric Chemistry and Physics, 9(4): 1339–1356

[45] Riccobono F , Schobesberger S , Scott C E , Dommen J , Ortega I K , Rondo L , Almeida J , Amorim A , Bianchi F , Breitenlechner M . et al. (2014). Oxidation products of biogenic emissions contribute to nucleation of atmospheric particles. Science, 344(6185): 717–721

[46] Riemer N , Ault A P , West M , Craig R L , Curtis J H . (2019). Aerosol mixing state: measurements, modeling, and impacts. Reviews of Geophysics, 57(2): 187–249

[47] Righi M , Hendricks J , Sausen R . (2013). The global impact of the transport sectors on atmospheric aerosol: simulations for year 2000 emissions. Atmospheric Chemistry and Physics, 13(19): 9939–9970

[48] Righi M , Hendricks J , Sausen R . (2016). The global impact of the transport sectors on atmospheric aerosol in 2030–Part 2: aviation. Atmospheric Chemistry and Physics, 16(7): 4481–4495

[49] Riipinen I , Pierce J R , Yli-Juuti T , Nieminen T , Häkkinen S , Ehn M , Junninen H , Lehtipalo K , Petäjä T , Slowik J . et al. (2011). Organic condensation: a vital link connecting aerosol formation to cloud condensation nuclei (CCN) concentrations. Atmospheric Chemistry and Physics, 11(8): 3865–3878

[50] Seinfeld J HPandis S N (2016). Atmospheric Chemistry and Physics: From Air Pollution to Climate Change. 3rd ed. Hoboken: John Wiley & Sons

[51] Shrivastava M , Fan J W , Zhang Y W , Rasool Q Z , Zhao B , Shen J W , Pierce J R , Jathar S H , Akherati A , Zhang J . et al. (2024). Intense formation of secondary ultrafine particles from Amazonian vegetation fires and their invigoration of deep clouds and precipitation. One Earth, 7(6): 1029–1043

[52] Song X K , Zhang S H , Huang H , Ding Q , Guo F , Zhang Y X , Li J , Li M Y , Cai W J , Wang C . (2024). A systematic review of the inequality of health burdens related to climate change. Frontiers of Environmental Science & Engineering, 18(5): 63

[53] Stevens B , Feingold G . (2009). Untangling aerosol effects on clouds and precipitation in a buffered system. Nature, 461(7264): 607–613

[54] Sullivan R CCrippa PMatsui HLeung L RZhao CThota APryor S C (2018). New particle formation leads to cloud dimming. npj Climate and Atmospheric Science, 1(1): 9

[55] Sun J , Hermann M , Weinhold K , Merkel M , Birmili W , Yang Y F , Tuch T , Flentje H , Briel B , Ries L . et al. (2024). Measurement report: contribution of atmospheric new particle formation to ultrafine particle concentration, cloud condensation nuclei, and radiative forcing–results from 5-year observations in central Europe. Atmospheric Chemistry and Physics, 24(18): 10667–10687

[56] Tinorua S , Denjean C , Nabat P , Pont V , Arnaud M , Bourrianne T , Dias Alves M , Gardrat E . (2024). A 2-year intercomparison of three methods for measuring black carbon concentration at a high-altitude research station in Europe. Atmospheric Measure-ment Techniques, 17(13): 3897–3915

[57] Tobías A , Rivas I , Reche C , Alastuey A , Rodríguez S , Fernández-Camacho R , de la Campa A M S , de la Rosa J , Sunyer J , Querol X . (2018). Short-term effects of ultrafine particles on daily mortality by primary vehicle exhaust versus secondary origin in three Spanish cities. Environment International, 111: 144–151

[58] Tröstl J , Chuang W K , Gordon H , Heinritzi M , Yan C , Molteni U , Ahlm L , Frege C , Bianchi F , Wagner R . et al. (2016). The role of low-volatility organic compounds in initial particle growth in the atmosphere. Nature, 533(7604): 527–531

[59] Twomey S . (1977). The influence of pollution on the shortwave albedo of clouds. Journal of the Atmospheric Sciences, 34(7): 1149–1152

[60] Virtanen A , Joutsensaari J , Kokkola H , Partridge D G , Blichner S , Seland Ø , Holopainen E , Tovazzi E , Lipponen A , Mikkonen S . et al. (2025). High sensitivity of cloud formation to aerosol changes. Nature Geoscience, 18(4): 289–295

[61] Wang J D , Wang J P , Cai R L , Liu C , Jiang J K , Nie W , Wang J B , Moteki N , Zaveri R A , Huang X . et al. (2023). Unified theoretical framework for black carbon mixing state allows greater accuracy of climate effect estimation. Nature Communications, 14(1): 2703

[62] Williamson C J , Kupc A , Axisa D , Bilsback K R , Bui T , Campuzano-Jost P , Dollner M , Froyd K D , Hodshire A L , Jimenez J L . et al. (2019). A large source of cloud condensation nuclei from new particle formation in the tropics. Nature, 574(7778): 399–403

[63] Wood R . (2012). Stratocumulus clouds. Monthly Weather Review, 140(8): 2373–2423

[64] Wood R , Mechoso C R , Bretherton C S , Weller R A , Huebert B , Straneo F , Albrecht B A , Coe H , Allen G , Vaughan G . et al. (2011). The VAMOS ocean-cloud-atmosphere-land study regional experiment (VOCALS-REx): goals, platforms, and field operations. Atmospheric Chemistry and Physics, 11(2): 627–654

[65] Yao L , Garmash O , Bianchi F , Zheng J , Yan C , Kontkanen J , Junninen H , Mazon S B , Ehn M , Paasonen P . et al. (2018). Atmospheric new particle formation from sulfuric acid and amines in a Chinese megacity. Science, 361(6399): 278–281

[66] Yinon LThemelis N JMcNeill V F (2010). Ultrafine particles from WTE and other combustion sources. In: Proceedings of the 18th Annual North American Waste-to-Energy Conference. Orlando: Solid Waste Processing Division and Environmental Engineering Division, 85–100

[67] Zhai J H , Lu X H , Li L , Zhang Q , Zhang C , Chen H , Yang X , Chen J M . (2017). Size-resolved chemical composition, effective density, and optical properties of biomass burning particles. Atmospheric Chemistry and Physics, 17(12): 7481–7493

[68] Zhao B , Donahue N M , Zhang K , Mao L Z , Shrivastava M , Ma P L , Shen J W , Wang S X , Sun J , Gordon H . et al. (2024). Global variability in atmospheric new particle formation mechanisms. Nature, 631(8019): 98–105

[69] Zheng G J , Wang Y , Wood R , Jensen M P , Kuang C , McCoy I L , Matthews A , Mei F , Tomlinson J M , Shilling J E . et al. (2021). New particle formation in the remote marine boundary layer. Nature Communications, 12(1): 527

[70] Zhu J L , Penner J E , Yu F Q , Sillman S , Andreae M O , Coe H . (2019). Decrease in radiative forcing by organic aerosol nucleation, climate, and land use change. Nature Communications, 10(1): 423

[71] Zhu Y F , Hinds W C , Kim S , Sioutas C . (2002). Concentration and size distribution of ultrafine particles near a major highway. Journal of the Air & Waste Management Association, 52(9): 1032–1042

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