Apparent dust size discrepancy in aerosol reanalysis in north African dust after long-range transport

Kramer, Samantha J.; Alvarez, Claudia; Barkley, Anne E.; Colarco, Peter R.; Custals, Lillian; Delgadillo, Rodrigo; Gaston, Cassandra J.; Govindaraju, Ravi; Zuidema, Paquita

doi:10.5194/acp-20-10047-2020

Cited by 20 publications

(14 citation statements)

References 64 publications

(81 reference statements)

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“…As the dust impacting Bermuda was transported much farther than sea salt, it is plausible that the characteristic dust peak is at a smaller size than sea salt. This is supported by past studies: (i) African dust reaching Miami, Florida exhibits most of its mass at geometric diameters below 2.1 µm (Kramer et al, 2020); and (ii) mass mean diameters of African dust are less than 1 µm by the time they reach the U.S. East Coast (Perry et al, 1997), which can take approximately a week of transport time (Carlson & Prospero, 1972).…”

Section: Volume Size Distributionssupporting

confidence: 63%

An Aerosol Climatology and Implications for Clouds at a Remote Marine Site: Case Study Over Bermuda

et al. 2021

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Aerosol characteristics and aerosol–cloud interactions remain uncertain in remote marine regions. We use over a decade of data (2000–2012) from the NASA AErosol RObotic NETwork, aerosol and wet deposition samples, satellite remote sensors, and models to examine aerosol and cloud droplet number characteristics at a representative open ocean site (Bermuda) over the Western North Atlantic Ocean (WNAO). Annual mean values were as follows: aerosol optical depth (AOD) = 0.12, Ångström Exponent (440/870 nm) = 0.95, fine mode fraction = 0.51, asymmetry factor = 0.72 (440 nm) and 0.68 (1020 nm), and Aqua‐MODIS cloud droplet number concentrations = 51.3 cm−3. The winter season (December–February) was characterized by high sea salt optical thickness and the highest aerosol extinction in the lowest 2 km. Extensive precipitation over the WNAO in winter helps contribute to the low FMFs in winter (∼0.40–0.50) even though air trajectories often originate over North America. Spring and summer had more pronounced influence from sulfate, dust, organic carbon, and black carbon. Volume size distributions were bimodal with a dominant coarse mode (effective radii: 1.85–2.09 µm) and less pronounced fine mode (0.14–0.16 µm), with variability in the coarse mode likely due to different characteristic sizes for transported dust (smaller) versus regional sea salt (larger). Extreme pollution events highlight the sensitivity of this site to long‐range transport of urban emissions, dust, and smoke. Differing annual cycles are identified between AOD and cloud droplet number concentrations, motivating a deeper look into aerosol–cloud interactions at this site.

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Section: Volume Size Distributionssupporting

confidence: 63%

An Aerosol Climatology and Implications for Clouds at a Remote Marine Site: Case Study Over Bermuda

et al. 2021

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“…), quartz, feldspar, calcite, and other mineral components (Murray et al, 2012;Scanza et al, 2015;Tang et al, 2016). Clay minerals were widely investigated in ice nucleation studies (Mason, 1960;Eastwood et al, 2008;Pinti et al, 2012;Wex et al, 2014;Kumar et al, 2019a) due to their high abundance in mineral dust composition (Murray et al, 2012), especially after long-range transport (Leinen et al, 1994;Uno et al, 2009). However, recent studies have demonstrated that K-feldspars are the most efficient mineral INP (Atkinson et al, 2013;Zolles et al, 2015b;Whale et al, 2017;Harrison et al, 2019;Yakobi-Hancock et al, 2013;Peckhaus et al, 2016;Kiselev et al, 2017;Augustin-Bauditz et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…In fact, reference single-mineral dust and surface-collected particles do not fully represent the actual dust transport process in the troposphere due to gravitational dust sedimentation, adsorption of biological materials, and other factors. During dust transport, larger particles settle faster due to gravity, while smaller particles can remain lifted for a longer period, thus possibly playing a different role in cloud formation (Kramer et al, 2020;Maki et al, 2019). Moreover, parameterizations are mainly based on the active mineral components of dust, but the effect of particle size is usually not considered.…”

Section: Introductionmentioning

confidence: 99%

Size-resolved atmospheric ice-nucleating particles during East Asian dust events

Chen

et al. 2021

Atmos. Chem. Phys.

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Abstract. Asian dust is an important source of atmospheric ice-nucleating particles (INPs). However, the freezing activity of airborne Asian dust, especially its sensitivity to particle size, is poorly understood. In this study we report the first INP measurement of size-resolved airborne mineral dust collected during East Asian dust events. The measured total INP concentrations in the immersion mode ranged from 10−2 to 102 L−1 in dust events at temperatures between −25 and −5 ∘C. The average contributions of heat-sensitive INPs at three temperatures, −10, −15, and −20 ∘C, were 81±12 %, 70±15 %, and 38±21 %, respectively, suggesting that proteinaceous biological materials have a substantial effect on the ice nucleation properties of Asian airborne mineral dust at high temperatures. The dust particles which originated from China's northwest deserts are more efficient INPs compared to those from northern regions. In general, there was no significant difference in the ice nucleation properties between East Asian dust particles and other regions in the world. An explicit size dependence of both INP concentration and surface ice-active-site density was observed. The nucleation efficiency of dust particles increased with increasing particle size, while the INP concentration first increased rapidly and then leveled, due to the significant decrease in the number concentration of larger particles. A new set of parameterizations for INP activity based on size-resolved nucleation properties of Asian mineral dust particles were developed over an extended temperature range (−35 to −6 ∘C). These size-dependent parameterizations require only particle size distribution as input and can be easily applied in models.

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“…It also remains a challenge for climate models to accurately 35 simulate the meteorological processes that play critical roles in dust processes. Yet, these uncertainties tend to amplify as models become more complex (Kok et al, 2017;Ryder et al, 2019;Adebiyi and Kok, 2020;di Biagio et al, 2020;Kramer et al, 2020;Li et al, 2021;Huang et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

How well do the CMIP6 models simulate dust aerosols?

Zhao

Ryder

Wilcox

2021

Preprint

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Abstract. Mineral dust impacts key processes in the Earth system, including the radiation budget, clouds, and nutrient cycles. We evaluate dust aerosols in 16 models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) against multiple reanalyses and satellite observations. Most models, and particularly the multi-model ensemble mean (MEM), capture the spatial patterns and seasonal cycles of global dust processes well. However, large uncertainties and inter-model diversity are found. For example, global dust emissions, primarily driven by model-simulated surface winds, vary by a factor of 5 across models, while the MEM estimate is double the amount in reanalyses. The ranges of CMIP6 model-simulated global dust emission, deposition, burden and optical depth (DOD) are larger than previous generations of models. Models present considerable disagreement in dust seasonal cycles over North China and North America. Here, DOD values are overestimated by most CMIP6 models, with the MEM estimate 1.2–1.7 times larger compared to satellite and reanalysis datasets. Such overestimates can reach up to a factor of 5 in individual models. Models also fail to reproduce some key features of the regional dust distribution, such as dust accumulation along the southern edge of the Himalayas. Overall, there are still large uncertainties in CMIP6 models’ simulated dust processes, which feature inconsistent biases throughout the dust lifecycle between models, particularly in the relationship connecting dust mass to DOD. Our results imply that modelled dust processes are becoming more uncertain as models become more sophisticated. More detailed output relating to the dust cycle in future intercomparison projects will enable better constraints of global dust cycles, and enable the potential identification of observationally-constrained links between dust cycles and optical properties.

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Apparent dust size discrepancy in aerosol reanalysis in north African dust after long-range transport

Cited by 20 publications

References 64 publications

An Aerosol Climatology and Implications for Clouds at a Remote Marine Site: Case Study Over Bermuda

An Aerosol Climatology and Implications for Clouds at a Remote Marine Site: Case Study Over Bermuda

Size-resolved atmospheric ice-nucleating particles during East Asian dust events

How well do the CMIP6 models simulate dust aerosols?

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