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Abstract. In this study, we developed a novel algorithm based on the collocatedModerate Resolution Imaging Spectroradiometer (MODIS) thermal infrared (TIR)observations and dust vertical profiles from the Cloud–Aerosol Lidar withOrthogonal Polarization (CALIOP) to simultaneously retrieve dust aerosoloptical depth at 10 µm (DAOD10 µm) and the coarse-mode dusteffective diameter (Deff) over global oceans. The accuracy of theDeff retrieval is assessed by comparing the dust lognormal volumeparticle size distribution (PSD) corresponding to retrieved Deff withthe in situ-measured dust PSDs from the AERosol Properties – Dust(AER-D), Saharan Mineral Dust Experiment (SAMUM-2), and Saharan Aerosol Long-Range Transport and Aerosol–Cloud-InteractionExperiment (SALTRACE) fieldcampaigns through case studies. The new DAOD10 µm retrievals wereevaluated first through comparisons with the collocated DAOD10.6 µmretrieved from the combined Imaging Infrared Radiometer (IIR) and CALIOPobservations from our previous study (Zheng et al., 2022). The pixel-to-pixelcomparison of the two DAOD retrievals indicates a good agreement(R∼0.7) and a significant reduction in (∼50 %) retrieval uncertainties largely thanks to the better constraint ondust size. In a climatological comparison, the seasonal and regional(2∘×5∘) mean DAOD10 µm retrievals basedon our combined MODIS and CALIOP method are in good agreement with the twoindependent Infrared Atmospheric Sounding Interferometer (IASI) productsover three dust transport regions (i.e., North Atlantic (NA; R=0.9),Indian Ocean (IO; R=0.8) and North Pacific (NP; R=0.7)). Using the new retrievals from 2013 to 2017, we performed a climatologicalanalysis of coarse-mode dust Deff over global oceans. We found thatdust Deff over IO and NP is up to 20 % smaller than that over NA.Over NA in summer, we found a ∼50 % reduction in the numberof retrievals with Deff>5 µm from 15 to35∘ W and a stable trend of Deff average at 4.4 µm from35∘ W throughout the Caribbean Sea (90∘ W). Over NP inspring, only ∼5 % of retrieved pixels with Deff>5 µm are found from 150 to 180∘ E, whilethe mean Deff remains stable at 4.0 µm throughout eastern NP. To the best of our knowledge, this study is the first to retrieve both DAOD andcoarse-mode dust particle size over global oceans for multiple years. Thisretrieval dataset provides insightful information for evaluating dustlongwave radiative effects and coarse-mode dust particle size in models.

Abstract. The role of mineral dust aerosol in the global radiative energy budget is oftenquantified by the dust direct radiative effect (DRE). The dust DRE stronglydepends on dust aerosol optical depth (DAOD), therefore, DRE efficiency(DREE = DRE / DAOD) is widely compared across different studies to eliminatedifferences due to the various dust loads. Nevertheless, DREE is stillinfluenced by the uncertainties associated with dust particle sizedistribution (PSD) and optical properties. In this study, we derive a globalclear-sky size-resolved DREE dataset in both shortwave (SW) and longwave (LW) at top ofthe atmosphere (TOA) and surface based on satellite observations (i.e.,satellite-retrieved dust extinction spatial and vertical distributions). Inthe DREE dataset, dust geometric diameter from 0.1 to 100 µmis divided into 10 bins and the corresponding monthly mean DREE (withrespect to DAOD at 532 nm) for each size bin is derived by using the RapidRadiative Transfer Model (RRTM). Three sets of state of the art dustrefractive indices (RI) and two sets of dust shape models (sphere vs. spheroid) are adopted to investigate the sensitivity of dust DREE to dustabsorption and shape. As a result, the size-resolved dust DREE datasetcontains globally distributed monthly mean dust DREE at TOA and surface foreach of 10 size bins with 5∘ (longitude) ×2∘(latitude) resolution as well as for each dust RI and shape combination. Thesize-resolved dust DREE dataset can be used to readily calculate global dustDRE for any DAOD and dust PSD, including the uncertainty in the DRE inducedby dust microphysical properties, (e.g., dust PSD, RI and shape). Bycalculating dust DRE based on DAOD climatology retrieved from differentsatellite sensors and based on different dust PSD, we find that uncertaintyin the spatial pattern of DAOD induces more than 10 % of the uncertaintyin SW dust DRE at TOA. The observation-based dust PSD induces around15–20 % uncertainty in dust DRE at TOA and in theatmosphere. The sensitivity assessments of dust DRE to dust RI and shapefurther suggest that dust nonsphericity induces a negligible effect on dustDRE estimations, while dust RI turns out to be the most important factor indetermining dust DRE, particularly in SW.

Biogenic volatile organic compounds (BVOCs) are emitted by vegetation and react with other compounds to form ozone and secondary organic matter (OM). In regional air quality models, biogenic emissions are often calculated using a plant functional type approach, which depends on the land use category. However, over cities, the land use is urban, so trees and their emissions are not represented. Here, we develop a bottom-up inventory of urban tree biogenic emissions in which the location of trees and their characteristics are derived from the tree database of the Paris city combined with allometric equations. Biogenic emissions are then computed for each tree based on their leaf dry biomass, tree-species-dependent emission factors, and activity factors representing the effects of light and temperature. Emissions are integrated in WRF-CHIMERE air quality simulations performed over June–July 2022. Over Paris city, the urban tree emissions have a significant impact on OM, inducing an average increase in the OM of about 5 %, reaching 14 % locally during the heatwaves. Ozone concentrations increase by 1.0 % on average and by 2.4 % during heatwaves, with a local increase of up to 6 %. The concentration increase remains spatially localized over Paris, extending to the Paris suburbs in the case of ozone during heatwaves. The inclusion of urban tree emissions improves the estimation of OM concentrations compared to in situ measurements, but they are still underestimated as trees are still missing from the inventory. OM concentrations are sensitive to terpene emissions, highlighting the importance of favoring urban tree species with low-terpene emissions. [ABSTRACT FROM AUTHOR]

The composition of soil dust aerosols derives from the mineral abundances in the parent soils that vary across dust source regions. Nonetheless, Earth system models (ESMs) have traditionally represented mineral dust as a globally homogeneous species. The growing interest in modeling dust mineralogy, facilitated by the recognized sensitivity of the dust climate impacts to composition, has motivated state-of-the-art ESMs to incorporate the mineral speciation of dust along with its effect upon the dust direct radiative effect (DRE). In this work, we enable the NASA Goddard Institute for Space Studies ModelE2.1 to calculate the shortwave (SW) DRE accounting for the regionally varying soil mineralogy. Mineral–radiation interaction at solar wavelengths is calculated according to two alternative coupling schemes: (1) external mixing of three mineral components that are optically distinguished, one of which contains embedded iron oxides; (2) a single internal mixture of all dust minerals with a dynamic fraction of iron oxides that varies regionally and temporally. We link dust absorption to the fractional mass of iron oxides based on recent chamber measurements using natural dust aerosol samples. We show that coupled mineralogy overall enhances the scattering by dust, and thus the global cooling, compared to our control run with globally uniform composition. According to the external mixing scheme, the SW DRE at the top of atmosphere (TOA) changes from -0.25 to -0.30Wm-2 , corresponding to a change in the net DRE, including the longwave effect, from -0.08 to -0.12Wm-2. The cooling increase is accentuated when the internal mixing scheme is configured: the SW DRE at the TOA becomes -0.34Wm-2 with a net DRE of -0.15Wm-2. The varying composition modifies the regional distribution of single scattering albedo (SSA), whose variations in specific regions can be remarkable (above 0.03) and significantly modify the regional SW DRE. Evaluation against the AErosol RObotic NETwork (AERONET) shows that explicit representation of soil mineralogy and its regional variations reduces the low bias of model dust SSA while improving the range of variability across stations and calendar months. Despite these improvements, the moderate spatiotemporal correlation with AERONET reveals remaining modeling challenges and the need for more accurate measurements of mineral fractions in soils. [ABSTRACT FROM AUTHOR]

Mineral dust aerosol is an important contributor to the Earth climate system and the correct representation of its size distribution is fundamental for shaping the current state and the evolution of climate. Despite many observational dust size data are available in the literature, using this body of information to proper guide the development and validation of climate models and remote sensing retrievals remains challenging. This is due to the diverse nature of different data, both in terms of measurement methods, diameter definitions, sampled concentrations and data treatments, leading to inherent heterogeneities. In this study we collect, evaluate, harmonize, and synthetize 58 size distribution data from the past 50 years of in situ field observations with the aim of providing a consistent dataset to the community to use for constraining the representation of dust size across its lifecycle. Four levels (LEV) of data treatment are defined, going from original data (LEV0), data interpolated and normalized on a standardized diameter path (LEV1), and data in which original particle diameters are converted into a common geometrical definition under both spherical (LEV2a) and aspherical (LEV2b) assumptions. Size distributions are classified to be representative of emission/source (SOURCE, <1 day from emission; number of datasets in this category, N=12), mid-range transport (MRT, 1-4 days of transport; N=36) and long-range transport (LRT, >4 days of transport; N=10). The harmonized dataset shows consistent features in the shape of the dust size distribution suggesting the conservation of airborne particles with time: a main mode located at ~10 µm (in volume) is observed for SOURCE dust, decreasing to ~5 µm and ~2 µm for MRT and LRT conditions, respectively, for which an additional mode becomes evident below 0.4 µm. Data for the three levels (LEV1, LEV2a, LEV2b) and the three categories (SOURCE, MRT, LRT), together with statistical metrics (mean, median, 25% and 75% percentiles, and standard deviation) are made available as: SOURCE (https://doi.org/10.57932/58dbe908-9394-4504-9099-74a3e77140e9; Formenti and Di Biagio, 2023a); MRT (https://doi.org/10.57932/31f2adf7-74fb-48e8-a3ef-059f663c47f1; Formenti and Di Biagio, 2023b); LRT (https://doi.org/10.57932/17dc781c-3e9d-4908-85b5-5c99e68e8f79; Formenti and Di Biagio, 2023c). [ABSTRACT FROM AUTHOR]

Biogenic Volatile Organic Compounds (BVOCs) are emitted by vegetation and react with other compounds to form ozone and secondary organic matter (OM). In regional air-quality models, biogenic emissions are often calculated using a Plant Functional Type approach, which depends on the land-use category. However, over cities, the land-use is urban, so trees and their emissions are not represented. Here, we develop a bottom-up inventory of urban-tree biogenic emissions, in which the location of trees and their characteristics are derived from the tree database of the Paris city combined with allometric equations. Biogenic emissions are then computed for each tree based on their leaf dry biomass, tree-species dependent emission factors and activity factors representing the effects of light and temperature. Emissions are integrated in WRF-CHIMERE air-quality simulations performed over June-July 2022. Over Paris city, the urban tree emissions have a significant impact on OM, inducing an average increase of OM of about 5%, reaching 14% locally during the heatwaves. Ozone concentrations increase by 1.0% on average, by 2.4% during heatwaves with local increase of up to 6%. The concentration increase remains spatially localized over Paris, extending to the Paris suburbs in the case of ozone during heatwaves. The inclusion of urban-tree emissions improves the estimation of OM concentrations compared to in situ measurements, but they are still underestimated as trees are still missing from the inventory. OM concentrations are sensitive to terpene emissions, highlighting the importance of favoring urban tree species with low terpene emissions. [ABSTRACT FROM AUTHOR]

In this study, we developed a novel algorithm based on the collocated Moderate Resolution Imaging Spectroradiometer (MODIS) thermal infrared (TIR) observations and dust vertical profiles from the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) to simultaneously retrieve dust aerosol optical depth at 10 µ m (DAOD 10µm) and the coarse-mode dust effective diameter (Deff) over global oceans. The accuracy of the Deff retrieval is assessed by comparing the dust lognormal volume particle size distribution (PSD) corresponding to retrieved Deff with the in situ-measured dust PSDs from the AERosol Properties – Dust (AER-D), Saharan Mineral Dust Experiment (SAMUM-2), and Saharan Aerosol Long-Range Transport and Aerosol–Cloud-Interaction Experiment (SALTRACE) field campaigns through case studies. The new DAOD 10µm retrievals were evaluated first through comparisons with the collocated DAOD 10.6µm retrieved from the combined Imaging Infrared Radiometer (IIR) and CALIOP observations from our previous study (Zheng et al., 2022). The pixel-to-pixel comparison of the two DAOD retrievals indicates a good agreement (R∼0.7) and a significant reduction in (∼50 %) retrieval uncertainties largely thanks to the better constraint on dust size. In a climatological comparison, the seasonal and regional (2∘×5∘) mean DAOD 10µm retrievals based on our combined MODIS and CALIOP method are in good agreement with the two independent Infrared Atmospheric Sounding Interferometer (IASI) products over three dust transport regions (i.e., North Atlantic (NA; R=0.9), Indian Ocean (IO; R=0.8) and North Pacific (NP; R=0.7)). Using the new retrievals from 2013 to 2017, we performed a climatological analysis of coarse-mode dust Deff over global oceans. We found that dust Deff over IO and NP is up to 20 % smaller than that over NA. Over NA in summer, we found a ∼50 % reduction in the number of retrievals with Deff>5 µ m from 15 to 35 ∘ W and a stable trend of Deff average at 4.4 µ m from 35 ∘ W throughout the Caribbean Sea (90 ∘ W). Over NP in spring, only ∼5 % of retrieved pixels with Deff>5 µ m are found from 150 to 180 ∘ E, while the mean Deff remains stable at 4.0 µ m throughout eastern NP. To the best of our knowledge, this study is the first to retrieve both DAOD and coarse-mode dust particle size over global oceans for multiple years. This retrieval dataset provides insightful information for evaluating dust longwave radiative effects and coarse-mode dust particle size in models. [ABSTRACT FROM AUTHOR]

The composition of soil dust aerosols derives from the mineral abundances in the parent soils that vary across dust source regions. Nonetheless, Earth System Models (ESMs) have traditionally represented mineral dust as a globally homogeneous species. The growing interest in modeling dust mineralogy, facilitated by the recognized sensitivity of the dust climate impacts to composition, has motivated state-of-the-art ESMs to incorporate the mineral speciation of dust along with its effect upon the dust direct radiative effect (DRE). In this work, we enable the NASA Goddard Institute for Space Studies ModelE2.1 to calculate the shortwave (SW) DRE by accounting for the regionally varying soil mineralogy. Mineral-radiation interaction at solar wavelengths is calculated according to two alternative coupling schemes: 1) external mixing of three mineral components that are optically distinguished, one of which contains embedded iron oxides; 2) a single internal mixture of all dust minerals with a dynamic fraction of iron oxides that varies regionally and temporally. We link dust absorption to the fractional mass of iron oxides based on recent chamber measurements using natural dust aerosol samples. We show that coupled mineralogy overall enhances the scattering by dust, and thus the global cooling, compared to our control run with globally uniform composition. According to the external mixing scheme, the SW DRE at the top of atmosphere (TOA) changes from -0.25 to -0.30W ·m-2, corresponding to a change in the net DRE, including the longwave effect, from -0.08 to -0.12W m-2. The cooling increase is accentuated when the internal mixing scheme is configured: SW DRE at TOA becomes -0.34W m-2 (with a net DRE of -0.15W ·m-2). The varying composition modifies the regional distribution of single scattering albedo (SSA), whose variations in specific regions can be remarkable (above 0.03) and significantly modify the regional DRE. Evaluation against the AErosol RObotic NETwork (AERONET) shows that explicit representation of soil mineralogy and its regional variations reduces the low bias of model dust SSA, while improving the range of variability across stations and calendar months. Despite these improvements, the moderate spatio-temporal correlation with AERONET reveals remaining modeling challenges and the need for more accurate measurements of mineral fractions in soils. [ABSTRACT FROM AUTHOR]