A New Method for Distinguishing Unactivated Particles in Cloud Condensation Nuclei Measurements: Implications for Aerosol Indirect Effect Evaluation

Abstract. H2SO4 vapor is important for the nucleation of atmospheric aerosols and the growth of ultrafine particles to cloud condensation nuclei (CCN) sizes with important roles in the global aerosol budget and hence planetary radiative forcing. Recent studies have found that reactions of stabilized Criegee intermediates (CIs, formed from the ozonolysis of alkenes) with SO2 may be an important source of H2SO4 that has been missing from atmospheric aerosol models. For the first time in a global model, we investigate the impact of this new source of H2SO4 in the atmosphere. We use the chemical transport model, GEOS-Chem, with the online aerosol microphysics module, TOMAS, to estimate the possible impact of CIs on present-day H2SO4, CCN, and the cloud-albedo aerosol indirect effect (AIE). We extend the standard GEOS-Chem chemistry with CI-forming reactions (ozonolysis of isoprene, methyl vinyl ketone, methacrolein, propene, and monoterpenes) from the Master Chemical Mechanism. Using a fast rate constant for CI+SO2, we find that the addition of this chemistry increases the global production of H2SO4 by 4%. H2SO4 concentrations increase by over 100% in forested tropical boundary layers and by over 10–25% in forested NH boundary layers (up to 100% in July) due to CI+SO2 chemistry, but the change is generally negligible elsewhere. The predicted changes in CCN were strongly dampened to the CI+SO2 changes in H2SO4 in some regions: less than 15% in tropical forests and less than 2% in most mid-latitude locations. The global-mean CCN change was less than 1% both in the boundary layer and the free troposphere. The associated cloud-albedo AIE change was less than 0.03 W m−2. The model global sensitivity of CCN and the AIE to CI+SO2 chemistry is significantly (approximately one order-of-magnitude) smaller than the sensitivity of CCN and AIE to other uncertain model inputs, such as nucleation mechanisms, primary emissions, SOA (secondary organic aerosol) and deposition. Similarly, comparisons to size-distribution measurements show that uncertainties in other model parameters dominate model biases in the model-predicted size distributions. We conclude that improvement in the modeled CI+SO2 chemistry would not likely lead to significant improvements in present-day CCN and AIE predictions.

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Cloud condensation nuclei prediction error from application of Köhler theory: Importance for the aerosol indirect effect

Journal of Geophysical Research Atmospheres ◽

10.1029/2006jd007834 ◽

2007 ◽

Vol 112 (D12) ◽

Cited By ~ 40

Author(s):

Rafaella-Eleni P. Sotiropoulou ◽

Athanasios Nenes ◽

Peter J. Adams ◽

John H. Seinfeld

Keyword(s):

Indirect Effect ◽

Prediction Error ◽

Cloud Condensation Nuclei ◽

Condensation Nuclei ◽

Aerosol Indirect Effect ◽

Kohler Theory

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Global cloud condensation nuclei influenced by carbonaceous combustion aerosol

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-6999-2011 ◽

2011 ◽

Vol 11 (3) ◽

pp. 6999-7044 ◽

Cited By ~ 3

Author(s):

D. V. Spracklen ◽

K. S. Carslaw ◽

U. Pöschl ◽

A. Rap ◽

P. M. Forster

Keyword(s):

Black Carbon ◽

Carbon Emissions ◽

Indirect Effect ◽

Cloud Condensation Nuclei ◽

Pollution Sources ◽

Condensation Nuclei ◽

Aerosol Indirect Effect ◽

Aerosol Model ◽

Cloud Albedo ◽

Global Mean

Abstract. Black carbon in carbonaceous combustion aerosol warms the climate by absorbing solar radiation, meaning reductions in black carbon emissions are often perceived as an attractive global warming mitigation option. However, carbonaceous combustion aerosol can also act as cloud condensation nuclei (particles upon which cloud drops form) so they also cool the climate by increasing cloud albedo. The net radiative effect of carbonaceous combustion aerosol is uncertain because their contribution to cloud drops has not been evaluated on the global scale. By combining extensive observations of cloud condensation nuclei concentrations and a global aerosol model, we show that carbonaceous combustion aerosol accounts for more than half of global cloud condensation nuclei. The evaluated model predicts that wildfire and pollution (fossil fuel and biofuel) carbonaceous combustion aerosol causes a global mean aerosol indirect effect of −0.34 W m−2 due to changes in cloud albedo, with pollution sources alone causing a global mean aerosol indirect effect of −0.23 W m−2. The small size of carbonaceous combustion particles from pollution sources means that whilst they account for only one-third of the emitted mass from these sources they cause two-thirds of the cloud albedo indirect effect that is due to carbonaceous combustion aerosol. This cooling effect must be accounted for to ensure that black carbon emissions controls that reduce the high number concentrations of small pollution particles have the desired net effect on climate.

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Weak sensitivity of cloud condensation nuclei and the aerosol indirect effect to Criegee + SO<sub>2</sub> chemistry

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-33127-2012 ◽

2012 ◽

Vol 12 (12) ◽

pp. 33127-33163 ◽

Cited By ~ 2

Author(s):

J. R. Pierce ◽

M. J. Evans ◽

C. E. Scott ◽

S. D. D'Andrea ◽

D. K. Farmer ◽

...

Keyword(s):

Boundary Layers ◽

Indirect Effect ◽

Ultrafine Particles ◽

Transport Model ◽

Cloud Condensation Nuclei ◽

Chemical Mechanism ◽

Model Parameters ◽

Condensation Nuclei ◽

Aerosol Indirect Effect ◽

Cloud Albedo

Abstract. H2SO4 vapor is important for the nucleation of atmospheric aerosols and the growth of ultrafine particles to cloud condensation nuclei (CCN) sizes. Recent studies have found that reactions of stabilized Criegee intermediates (CIs, formed from the ozonolysis of alkenes) with SO2 may be an important source of H2SO4 that has been missing from atmospheric aerosol models. In this paper, we use the chemical transport model, GEOS-Chem, with the online aerosol microphysics module, TOMAS, to estimate the possible impact of CIs on present-day H2SO4, CCN, and the cloud-albedo aerosol indirect effect (AIE). We extend the standard GEOS-Chem chemistry with CI-forming reactions (ozonolysis of isoprene, methyl vinyl ketone, methacrolein, propene, and monoterpenes) from the Master Chemical Mechanism. Using a fast rate constant for CI+SO2, we find that the addition of this chemistry increases the global production of H2SO4 by 4%. H2SO4 concentrations increase by over 100% in forested tropical boundary layers and by over 10–25% in forested NH boundary layers (up to 100% in July) due to CI + SO2 chemistry, but the change is generally negligible elsewhere. The predicted changed in CCN were strongly dampened to the CI + SO2 changes in H2SO4 in these regions: less than 15% in tropical forests and less than 2% in most mid-latitude locations. The global-mean CCN change was less than 1% both in the boundary layer and the free troposphere. The associated cloud-albedo AIE change was less than 0.03 W m−2. The model global sensitivity of CCN and the AIE to CI + SO2 chemistry is significantly (approximately one order-of-magnitude) smaller than the sensitivity of CCN and AIE to other uncertain model inputs, such as nucleation mechanisms, primary emissions, SOA and deposition. Similarly, comparisons to size-distribution measurements show that uncertainties in other model parameters dominate model biases in the model-predicted size distributions. We conclude that improvement in the modeled CI + SO2 chemistry would not likely to lead to significant improvements in present-day CCN and AIE predictions.

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Exploring the First Aerosol Indirect Effect over the Maritime Continent Using a Ten-Year Collocated MODIS, CALIOP, and Model Dataset

10.5194/acp-2018-4 ◽

2018 ◽

Author(s):

Alexa D. Ross ◽

Robert E. Holz ◽

Gregory Quinn ◽

Jeffrey S. Reid ◽

Peng Xian ◽

...

Keyword(s):

Indirect Effect ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Effective Radius ◽

Satellite Observations ◽

Orthogonal Polarization ◽

High Background ◽

Aerosol Indirect Effect ◽

Moderate Resolution Imaging Spectroradiometer ◽

Complex Relationships

Abstract. Satellite observations and model simulations cannot, by themselves, give full insight into the complex relationships between aerosols and clouds. This is especially the case over the greater Southeast Asia, an area that is particularly sensitive to changes in precipitation yet possesses some of the world’s largest observability and predictability challenges. We present a new collocated dataset that combines satellite observations from Aqua's Moderate-resolution Imaging Spectroradiometer (MODIS) and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) with the Navy Aerosol Analysis and Prediction System (NAAPS). The dataset is designed with the capability to investigate aerosol-cloud relationships and provides coincident and vertically resolved cloud and aerosol observations for a ten-year period. Using model reanalysis aerosol fields from the NAAPS and coincident cloud liquid effective radius retrievals from MODIS (removing cirrus contamination using CALIOP), we investigate the first aerosol indirect effect. We find overall that as expected, aerosol loading anti-correlates with cloud effective radius, with maximum sensitivity in cumulous mediocris clouds with heights in the 3–4.5 km level. The highest susceptibility in droplet effective radius to modeled perturbations in particle concentrations were found in the more remote regions of the western Pacific Ocean and Indian Ocean. Conversely, there was much less variability in cloud droplet size near emission sources over both land and water. We hypothesize this is suggestive of a high background aerosol population already saturating the cloud condensation nuclei budget.

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Global cloud condensation nuclei influenced by carbonaceous combustion aerosol

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-9067-2011 ◽

2011 ◽

Vol 11 (17) ◽

pp. 9067-9087 ◽

Cited By ~ 155

Author(s):

D. V. Spracklen ◽

K. S. Carslaw ◽

U. Pöschl ◽

A. Rap ◽

P. M. Forster

Keyword(s):

Black Carbon ◽

Carbon Emissions ◽

Indirect Effect ◽

Fossil Fuel ◽

Cloud Condensation Nuclei ◽

Pollution Sources ◽

Aerosol Indirect Effect ◽

Cloud Albedo ◽

Combustion Particles ◽

Global Mean

Abstract. Black carbon in carbonaceous combustion aerosol warms the climate by absorbing solar radiation, meaning reductions in black carbon emissions are often perceived as an attractive global warming mitigation option. However, carbonaceous combustion aerosol can also act as cloud condensation nuclei (CCN) so they also cool the climate by increasing cloud albedo. The net radiative effect of carbonaceous combustion aerosol is uncertain because their contribution to CCN has not been evaluated on the global scale. By combining extensive observations of CCN concentrations with the GLOMAP global aerosol model, we find that the model is biased low (normalised mean bias = −77 %) unless carbonaceous combustion aerosol act as CCN. We show that carbonaceous combustion aerosol accounts for more than half (52–64 %) of global CCN with the range due to uncertainty in the emitted size distribution of carbonaceous combustion particles. The model predicts that wildfire and pollution (fossil fuel and biofuel) carbonaceous combustion aerosol causes a global mean cloud albedo aerosol indirect effect of −0.34 W m−2, with stronger cooling if we assume smaller particle emission size. We calculate that carbonaceous combustion aerosol from pollution sources cause a global mean aerosol indirect effect of −0.23 W m−2. The small size of carbonaceous combustion particles from fossil fuel sources means that whilst pollution sources account for only one-third of the emitted mass they cause two-thirds of the cloud albedo aerosol indirect effect that is due to carbonaceous combustion aerosol. This cooling effect must be accounted for, along with other cloud effects not studied here, to ensure that black carbon emissions controls that reduce the high number concentrations of fossil fuel particles have the desired net effect on climate.

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Coincidence Errors in a Cloud Droplet Probe (CDP) and a Cloud and Aerosol Spectrometer (CAS), and the Improved Performance of a Modified CDP

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-11-00208.1 ◽

2012 ◽

Vol 29 (10) ◽

pp. 1532-1541 ◽

Cited By ~ 30

Author(s):

Sara Lance

Keyword(s):

Systematic Error ◽

Indirect Effect ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Current Paper ◽

Aerosol Indirect Effect ◽

Improved Performance ◽

Measurement Artifact ◽

The Relationship

Abstract Central to the aerosol indirect effect on climate is the relationship between cloud droplet concentrations Nd and cloud condensation nuclei (CCN) concentrations. There are valid reasons to expect a sublinear relationship between measured Nd and CCN, and such relationships have been observed for clouds in a variety of locations. However, a measurement artifact known as “coincidence” can also produce a sublinear trend. The current paper shows that two commonly used instruments, the cloud droplet probe (CDP) and the cloud and aerosol spectrometer (CAS), can be subject to significantly greater coincidence errors than are typically recognized, with an undercounting bias of at least 27% and an oversizing bias of 20%–30% on average at Nd = 500 cm−3, and with an undercounting bias of as much as 44% at Nd = 1000 cm−3. This type of systematic error may have serious implications for interpretation of in situ cloud observations. It is shown that a simple optical modification of the CDP dramatically reduces oversizing and undercounting biases due to coincidence. Guidance is provided for diagnosing coincidence errors in CAS and CDP instruments.

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Indications of a Decrease in the Depth of Deep Convective Cores with Increasing Aerosol Concentration During the CACTI Campaign

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-21-0119.1 ◽

2021 ◽

Keyword(s):

Indirect Effect ◽

Deep Layer ◽

Mixed Boundary ◽

Convective Available Potential Energy ◽

Vertical Wind Shear ◽

Aerosol Concentration ◽

Meteorological Variables ◽

Condensation Nuclei ◽

Study Region ◽

Aerosol Indirect Effect

Abstract An aerosol indirect effect on deep convective cores (DCCs), by which increasing aerosol concentration increases cloud-top height via enhanced latent heating and updraft velocity, has been proposed in many studies. However, the magnitude of this effect remains uncertain due to aerosol measurement limitations, modulation of the effect by meteorological conditions, and difficulties untangling meteorological and aerosol effects on DCCs. The Cloud, Aerosol, and Complex Terrain Interactions (CACTI) campaign in 2018-19 produced concentrated aerosol and cloud observations in a location with frequent DCCs, providing an opportunity to examine the proposed aerosol indirect effect on DCC depth in a rigorous and robust manner. For periods throughout the campaign with well mixed boundary layers, we analyze relationships that exist between aerosol variables (condensation nuclei concentration >10 nm, 0.4% cloud condensation nuclei concentration, 55-1000 nm aerosol concentration, and aerosol optical depth) and meteorological variables [level of neutral buoyancy (LNB), convective available potential energy, mid-level relative humidity, and deep layer vertical wind shear] with the maximum radar echo top height and cloud-top temperature (CTT) of DCCs. Meteorological variables such as LNB and deep-layer shear are strongly correlated with DCC depth. LNB is also highly correlated with three of the aerosol variables. After accounting for meteorological correlations, increasing values of the aerosol variables (with the exception of one formulation of AOD) are generally correlated at a statistically significant level with a warmer CTT of DCCs. Therefore, for the study region and period considered, increasing aerosol concentration is mostly associated with a decrease in DCC depth.

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A Critical Examination of the Observed First Aerosol Indirect Effect

Journal of the Atmospheric Sciences ◽

10.1175/2008jas2812.1 ◽

2009 ◽

Vol 66 (4) ◽

pp. 1018-1032 ◽

Cited By ~ 20

Author(s):

Hongfei Shao ◽

Guosheng Liu

Keyword(s):

Indirect Effect ◽

Climate Models ◽

Cloud Condensation Nuclei ◽

Number Concentration ◽

Global Climate Models ◽

Cooling Effect ◽

Critical Examination ◽

Aerosol Indirect Effect ◽

Ability To Act ◽

Relative Change

Abstract The relative change in cloud droplet number concentration with respect to the relative change in aerosol number concentration, α, is an indicator of the strength of the aerosol indirect effect and is commonly used in models to parameterize this effect. Based on Twomey’s analytical expression, the values of α derived from measurements of an individual cloud (i.e., αT) can be as large as 0.60–0.90. In contrast, the values of α derived from direct measurements of polluted and clean clouds (i.e., αΔ) typically range from 0.25 to 0.85, corresponding to a weaker but more uncertain cooling effect. Clearly, reconciling αΔ with αT is necessary to properly calculate the indirect aerosol forcing. In this study, the terms that are involved in determining αT and αΔ are first analytically examined. Then, by analyzing satellite data over subtropical oceans, the satellite-observed αΔ can be successfully related to Twomey’s analytical solution. It is found that except for the dust-influenced region of the northeastern Atlantic Ocean, injecting continental aerosols into a marine background may significantly reduce the average aerosols’ ability to act as cloud condensation nuclei. Taking this competing effect into account may reduce the cooling effect proposed by Twomey from 0.76 to 0.28. It is also found that the variability of the adiabaticity (i.e., the cloud dilution state with respect to adiabatic cloud) among different clouds accounts for ∼50% uncertainty in αΔ. Based on these results, the authors explain the claimed discrepancies in the first aerosol indirect effect (AIE) from different methods and on different scales and present an improved parameterization of the first AIE that can be used in global climate models.

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