Francesca Barnaba | National Research Council (original) (raw)

Papers by Francesca Barnaba

Atmospheric Environment, Feb 1, 2012

Aerosol transport simulations within Europe were performed with the regional transport model COSM... more Aerosol transport simulations within Europe were performed with the regional transport model COSMO-MUSCAT for two different time periods, July 19e26, 2006 and February 16e26, 2007. Simulated PM 2.5 , backscatter profiles and aerosol optical depths (AODs) were compared to observations, showing good agreements in magnitude, shape and day-today variations. Maximum AODs (>0.4) were found over Middle Europe and minimum AODs (<0.13) over the ocean during both time periods, corresponding to regions of high (PM 2.5 > 10 mg m À3) and low (PM 2.5 < 4.0 mg m À3) concentration near the surface. Vertical aerosol distributions were evaluated with lidar measurements from the EARLINET ground network and CALIPSO satellite retrievals. The characteristic vertical distribution and the differences for the summer and the winter cases were represented well by the regional model. Mean differences between À5.0 Â 10 À7 toÀ2.0 Â 10 À7 m À1 sr À1 (summer case) and À2.3 Â 10 À6 to 1.0 Â 10 À6 m À1 sr À1 (winter case) from 0.0 to 2.5 km altitude were found between observed (space-based lidar) and simulated backscatter coefficients. For the cases that were investigated in this study different prescriptions of the vertical distribution at the lateral model boundaries resulted in only small differences in aerosol distributions within the interior of the model region.

Aerosol Optical Depth (AOD) retrieval from sunphotometric measurements is sensitive to the concen... more Aerosol Optical Depth (AOD) retrieval from sunphotometric measurements is sensitive to the concentration of atmospheric gases (e.g. NO2), particularly in UV and lower visible spectral range. Current algorithms used in aerosol networks either use climatological NO2 to estimate the corresponding absorption or it is totally ignored . NO2 in the atmosphere is characterized by high spatial and temporal variations, especially in urban areas. Thus, climatological values are rarely representative of the actual NO2 concentration, introducing non-negligible errors in AOD retrievals at specific spectral regions.We propose a correction approach, using synchronous data from different networks/instruments. AOD is retrieved by sunphotometers (CIMEL and PREDE-POM) in AERONET and SKYNET networks. NO2 total column is calculated by direct sun measurements of PANDORA spectroradiometers, part of PANDONIA network. Data from three stations, with colocation of these instruments are used in presented study to apply the correction and evaluate the new datasets. Two stations in Rome, Italy (Sapienza University at City Center and CNR-ISAC at Tor Vergata in suburban area) and one in Athens, Greece (National Observatory of Athens at city center). More specifically the NO2 correction is applied on AOD at four bandwidths (340, 380, 400 and 440 nm). Propagation of the correction to the calculated Ångström Exponent is also estimated.Highest mean relative differences are found at 440nm which are up to 1.7% for AERONET data and 5.3% at 400 nm for SKYNET (which’s algorithm does not consider NO2). Highest absolute AOD difference found was 0.037 at 440nm. For Ångström Exponent 440-870 absolute maximum difference found was 0.31.Finally, cases of days with high NO2 variability and the corresponding effect on AOD calculations will be presented.

&lt;p&gt;ALICEnet is a network of Automated Lidar Ceilometers (ALCs) operating ac... more &lt;p&gt;ALICEnet is a network of Automated Lidar Ceilometers (ALCs) operating across Italy. The geographical distribution of the measuring stations, extending from the north to the south of the country, allows monitoring of aerosol vertical profiles over a wide range of environmental and atmospheric conditions, dominated, for example, by anthropogenic particle production, Saharan dust transport or volcanic ash advections. The network, coordinated by CNR-ISAC and involving different institutions, is also a contributor of E-PROFILE, a EUMETNET program for surface-based profile observations.&lt;/p&gt;&lt;p&gt;The ALICEnet infrastructure and data processing flow (including signal correction and automatic calibration procedures) are here described, together with the inversion and retrieval algorithms. These latter allow to retrieve the aerosol properties over the vertical profile, to identify different layers, and to assess the atmospheric boundary layer (ABL) characteristics, such as the ABL and mixing layer height. Based on this setup, both use of near-real time data (e.g., to monitor aerosol transport events) and long-term studies (e.g., evaluation of aerosol climatological, site-dependent characteristics) will be possible.&lt;/p&gt;&lt;p&gt;In the present contribution, we focus on two examples of application: a case of long-range transport of Saharan dust and smoke, occurred over Rome in July 2017 during the EMERGE campaign, and the analysis of the climatological features of the mesoscale circulation between the Po Valley and the Alps. For both cases the ALICEnet retrieval procedure is validated based on independent measurements from the ground. Benefits from coupling with other remote sensing instruments, satellite radiometers, and atmospheric dispersion models are discussed.&lt;/p&gt;

Characterizing chemical and physical aerosol properties is important to understand their sources,... more Characterizing chemical and physical aerosol properties is important to understand their sources, effects, and feedback mechanisms in the atmosphere. This study proposes a scheme to classify aerosol populations based on their spectral optical properties (absorption and scattering). The scheme is obtained thanks to the outstanding set of information on particle size and composition these properties contain. The spectral variability of the aerosol Single Scattering Albedo (dSSA), and the Scattering and Absorption Angstrom Exponents (SAE and AAE, respectively) were observed on the basis of two-year measurements of aerosol optical properties (scattering and absorption coefficients at blue, green and red wavelengths) performed in the suburbs of Rome (Italy). Optical measurements of various aerosol types were coupled to measurements of particle number size distributions and relevant optical properties simulations (Mie theory). These latter allowed to investigate the role of the particle size and composition in the bulk aerosol properties observed. The combination of simulations and measurements suggested a general "paradigm" built on dSSA, SAE and AAE to optically classify aerosols. The paradigm proved suitable to identify the presence of key aerosol populations, including soot, biomass burning, organics, dust and marine particles. The work highlights that: (i) aerosol populations show distinctive combinations of SAE and dSSA times AAE, these variables being linked by a linear inverse relation varying with varying SSA; (ii) fine particles show SAE > 1.5, whilst SAE < 1 is found for both coarse particles and ultrafine soot-rich aerosols; (iii) fine and coarse particles both show SSA > 0.8, whilst ultrafine urban Aitken mode and soot particles show SSA < 0.8. A strict agreement was found when comparing the proposed paradigm to aerosol observations performed during past major field campaigns.

Atmosphere, Feb 25, 2018

Surface concentration of black carbon (BC) is a key factor for the understanding of the impact of... more Surface concentration of black carbon (BC) is a key factor for the understanding of the impact of anthropogenic pollutants on human health. The majority of Italian cities lack long-term measurements of BC concentrations since such a metric is not regulated by EU legislation. This work attempts a long-term (2001-2017) inference of equivalent black carbon (eBC) concentrations in the city of Rome (Italy) based on sun-photometry data. To this end, aerosol light absorption coefficients at the surface are inferred from the "columnar" aerosol aerosol light absorption coefficient records from the Rome Tor Vergata AERONET sun-photometer. The main focus of this work is to rescale aerosol light absorption columnar data (AERONET) to ground-level BC data. This is done by using values of mixing layer height (MLH) derived from ceilometer measurements and then by converting the absorption into eBC mass concentration through a mass-to-absorption conversion factor, the Mass Absorption Efficiency (MAE). The final aim is to obtain relevant data representative of the BC aerosol at the surface (i.e., in-situ)-so within the MLH-and then to infer a long-term record of "surface" equivalent black carbon mass concentration in Rome. To evaluate the accuracy of this procedure, we compared the AERONET-based results to in-situ measurements of aerosol light absorption coefficients (α abs) collected during some intensive field campaigns performed in Rome between 2010 and 2017. This analysis shows that different measurement methods, local emissions, and atmospheric conditions (MLH, residual layers) are some of the most important factors influencing differences between inferred and measured α abs. As a general result, "inferred" and "measured" α abs resulted to reach quite a good correlation (up to r = 0.73) after a screening procedure that excludes one of the major cause of discrepancy between AERONET inferred and in-situ measured α abs : the presence of highly absorbing aerosol layers at high altitude (e.g., dust), which frequently affects the Mediterranean site of Rome. Long-term trends of "inferred" α abs , eBC, and of the major optical variables that control aerosol's direct radiative forcing (extinction aerosol optical depth, AOD EXT , absorption aerosol optical depth, AOD ABS , and single scattering albedo, SSA) have been estimated. The Mann-Kendall statistical test associated with Sen's slope was used to test the data for long-term trends. These show a negative trend for both AOD EXT (−0.047/decade) and AOD ABS (−0.007/decade). The latter converts into a negative trend for the α abs of −5.9 Mm −1 /decade and for eBC mass concentration of −0.76 µg/m 3 /decade. A positive trend is found for SSA (+0.014/decade), indicating that contribution of absorption to extinction is decreasing faster than that of scattering. These long-term trends are consistent with those of other air pollutant concentrations (i.e., PM 2.5 and CO) in the Rome area.

Atmospheric Research, May 1, 2020

The "Carbonaceous Aerosol in Rome and Environs" (CARE) experiment took place at a Mediterranean u... more The "Carbonaceous Aerosol in Rome and Environs" (CARE) experiment took place at a Mediterranean urban background site in Rome (Italy) deploying a variety of instrumentation to assess aerosol physical-chemical and optical properties with high-time resolution (from 1 min to 2 h). In this study, aerosol optical properties, chemical composition, and size distribution data were examined with a focus on the analysis of several intensive optical properties obtained from multi-wavelength measurements of aerosol scattering and absorption coefficients. The spectral behaviour of several quantities related to both aerosol composition and size was explored, analysing their high-time resolved temporal patterns and combining them in order to extract the maximum information from all the available data. A methodology to separate aerosol types using optical data only is here proposed and applied to an urban area characterised by a complex mixture of particles. A key is given to correctly disentangle cases that could not be distinguished observing only one or few parameters, but that can be clearly separated using a suitable ensemble of optical properties. The SSCAAE, i.e. the wavelength dependence of the Single Scattering co-albedo 1-SSA (where SSA is the Single Scattering Albedo)-that efficiently responds to both aerosol size and chemical composition-resulted to be the best optical intensive parameter to look at for the discrimination between episodes characterised by specific aerosol types (e.g. sea salt, Saharan dust) and more mixed conditions dominated by local emissions. However, this study also highlighted that it is necessary to combine temporal patterns of different optical parameters to robustly associate SSCAAE features to specific aerosol types. In addition, the complete chemical speciation and the hightime resolved size distribution were used to confirm the aerosol types identified via a combination of aerosol optical properties. Look-up tables with most suitable ranges of values for optical variables were produced; therefore, these pieces of information can be used at the same site or at locations with similar features to quickly identify the occurrence of aerosol episodes. Graphical frameworks (both from the literature and newly designed) are also proposed; for each scheme features, advantages, and limitations are discussed.

Journal of Quantitative Spectroscopy & Radiative Transfer, Nov 1, 2006

In spite of being located at the heart of the highest mountain range in the world, the Himalayan ... more In spite of being located at the heart of the highest mountain range in the world, the Himalayan Nepal Climate Observatory (5079 m a.s.l.) at the Ev-K2-CNR Pyramid is shown to be affected by the advection of pollution aerosols from the populated regions of southern Nepal and the Indo-Gangetic plains. Such an impact is observed along most of the period April 2006-March 2007 addressed here, with a minimum in the monsoon season. Backtrajectory-analysis indicates long-range transport episodes occurring in this period to originate mainly in the West Asian deserts. At this high altitude site, the measured aerosol optical depth is observed to be: 1) about one order of magnitude lower than the one measured at Gandhi College (60 m a.s.l.), in the Indo-Gangetic basin, and 2) maximum during the monsoon period, due to the presence of elevated (cirrus-like) particle layers. Assessment of the aerosol radiative forcing results to be hampered by the persistent presence of these high altitude particle layers, which impede a continuous measurement of both the aerosol optical depth and its radiative properties from sky radiance inversions. Even though the retrieved absorption coefficients of pollution aerosols was rather large (single scattering albedo of the order of 0.6-0.9 were observed in the month of April 2006), the corresponding low optical depths (∼0.03 at 500 nm) are expected to limit the relevant radiative forcings. Still, the high specific forcing of this aerosol and its capability of altering snow surface albedo provide good reason for continuous monitoring.

We characterize the atmospheric nondust aerosol having the strongest spectral dependence of light... more We characterize the atmospheric nondust aerosol having the strongest spectral dependence of light absorption (as indicated by the Absorption Angstrom Exponent, AAE) at visible wavelengths in the urban Po Valley. In situ ground measurements of aerosol spectral optical properties, PM 1 chemical composition (HR-ToF-AMS), and coarse and fine size distributions, were carried out in Bologna, and data statistically analysed. Findings prove that a "brown" aerosol (AAE from 2.5 to 6) in the ambient atmosphere is composed by "droplet" mode particles enriched in aged organic aerosol (OA) and nitrate. We provide a comprehensive physico-chemical characterisation of this brown aerosol, including its spectral optical signature, and possible sources. To our knowledge, no previous work has considered these issues in the ambient atmosphere. We compared to literature to put findings in a broader perspective. There is consistency with recent "diluted" urban observations (airborne, and AERONET), and combustion chamber observations. Our study adds to these previous ones that the high AAE values featuring the "brown" aerosol depend on the OA to Black Carbon (BC) ratio more than on OA, and that the link between AAE and OA-to-BC (already observed for freshly emitted primary aerosols from biomass burning) does exist in the ambient atmosphere for this aged "brown" aerosol, as well. The comparison with studies on the composition evolution of OA in the atmosphere strengthens the result that this "brown" aerosol is an aged OA, and provides experimental evidence for the aged "brown" OA formation in the ambient atmosphere. Findings will have important atmospheric implications for modeling studies, and remote sensing observations, as regards the parametrization and identification of Brown OA, and Brown Carbon in the atmosphere. 1 Introduction Aerosol has an important role in the Earth's climate with both direct and indirect effects; beside that, it affects air quality and atmospheric chemistry. At present, our understanding of the light-absorbing aerosol types is very incomplete (see reviews by Laskin et al., 2015; Moise et al., 2015). An important absorber of solar radiation in the visible region is the atmospheric carbonaceous aerosol (IPCC 2013). Visible-light absorbing properties of this aerosol type vary between two extremes. On one side, there is Black Carbon (BC) that strongly absorbs light over a broad spectral range. On the other side, there is the colourless Organic Carbon (OC) with no absorption or little absorption in the UV spectral range. Between these extremes, there

Sand and Dust Storms (SDS) are extreme meteorological phenomena that can be asso... more Sand and Dust Storms (SDS) are extreme meteorological phenomena that can be associated with high amounts of atmospheric mineral dust. SDS are an essential element of the Earth&#8217;s natural biogeochemical cycles but are also caused in part by human-induced drivers including climate change, unsustainable land management, and water use; in turn, SDS contribute to climate change and air pollution. Over the last few years, there has been an increasing need for SDS accurate information and predictions, particularly over desert regions as the Sahara and in the Middle East and regions affected by long-range dust transport as Europe, to support early warning systems, and preparedness and mitigation plans in addition to growing interest from diverse stakeholders in the aviation sector, including airlines, airports, engine manufacturers, as well as the military. SDS affect aviation operations mainly through reduced visibility and several types of mechanical effects that impact different parts of the aircraft (Clarkson and Simpson 2017); these have significant mid- to long-term implications for issues such as engine and aircraft maintenance, airport operations and resilience, and flight route planning and optimization.&#160;In this contribution, we will present ongoing efforts on utilizing desert dust modelling products based on the MONARCH chemical weather prediction system and satellite observational constraint (P&#233;rez et al, 2011; Di Tomaso et al., 2017) as the basis to understand the short- and long-term risks of operating in risky sand and dust environments. We will introduce two types of examples of the use of SDS information. First, a long-term assessment for Northern Africa, the Middle East and Europe of the SDS-threats surrounding visibility and aircraft/engine exposure to dust, based on a 10-year MONARCH dust reanalysis in the context of the EU ERA4CS DustClim project. We will subsequently revise the benefits of using daily dust forecasts based on MONARCH (the reference operational model of the WMO Barcelona Dust Forecast Center, https://dust.aemet.es/) for the early prediction of extreme events as the ones occurred in March 2018 in the Eastern Mediterranean and in February 2020 in the Canary Islands.Acknowledgement The authors acknowledge the DustClim project which is part of ERA4CS, an ERA-NET. COST Action inDust (CA16202) and the WMO SDS-WAS Regional Center are also acknowledged. We are thankful to T. Bolic for her suggestions and ideas regarding resilience of the aviation sector to SDS.References Clarkson, R., and Simpson, H., 2017: Maximising Airspace Use During Volcanic Eruptions: Matching Engine Durability against Ash Cloud Occurrence, NATO STO AVT-272 Specialists Meeting on &#8220;Impact of Volcanic Ash Clouds on Military Operations&#8221; Volume: 1.Di Tomaso et al., (2017): Assimilation of MODIS Dark Target and Deep Blue observations in the dust aerosol component of NMMB-MONARCH version 1.0, Geosci. Model Dev., 10, 1107-1129, doi:10.5194/gmd-10-1107-2017.P&#233;rez et al.,: An online mineral dust aerosol model for meso to global scales: Model description, annual simulations and evaluation, Atmos. Chem. Phys., 11, 13001-13027, doi: 10.5194/acp-11-13001-2011, 2011.Votsis et al., (2020), Operational risks of sand and dust storms in aviation and solar energy: the DustClim approach, FMI's Climate Bulletin: Research Letters 1/2020, DOI: 10.35614/ISSN-2341-6408-IK-2020-02-RL.

EGU General Assembly Conference Abstracts, Apr 1, 2016

Journal of Geophysical Research, Oct 13, 2010

Remote sensing represents a prospective tool to complement in situ measurements for monitoring pa... more Remote sensing represents a prospective tool to complement in situ measurements for monitoring particulate matter air pollution. The remotely sensed aerosol metric which is generally related to the in situ measured particulate matter mass concentration (PM) is the aerosol optical thickness (AOT), the vertically integrated aerosol extinction that optically quantifies the aerosol load in the whole atmospheric column. Annual variations in AOT and PM can follow very different patterns, indicating that the AOT-to-PM conversion is not straightforward. In the Po Valley, northern Italy, AOT and PM seasonal cycles exhibit a marked phase shift. Making use of aerosol extinction vertical profiles derived from continuous aerosol lidar measurements, we further searched through the AOT-to-PM 10 relationship in this region. On the basis of a 2-year (2006-2007) multisensor database, including remote sensing observations from ground and space and in situ measurements, this study: (1) discloses for the first time the height-resolved seasonal variability of the aerosol optical properties in the Po Valley, (2) demonstrates and quantifies the crucial role of the aerosol vertical distribution in the AOT-to-PM relationship in this region, (3) suggests a methodology to rescale AOT to ground-level aerosol extinction values that correlate with PM concentration and from which PM 10 annual average and exceedances frequency of daily limit value can be retrieved within a few percentage points, and (4) highlights that the hygroscopic growth of the particles in the atmosphere is a critical factor for comparing in situ-measured to remotely sensed aerosol properties.

Sand and Dust Storms (SDS) are extreme meteorological phenomena associated with ... more Sand and Dust Storms (SDS) are extreme meteorological phenomena associated with high amounts of atmospheric mineral dust. SDS are an essential element of the Earth&#8217;s natural biogeochemical cycles but are also partly caused by human factors including anthropogenic climate change and unsustainable land and water management; in turn, SDS contribute to climate change and air pollution. SDS have become a serious global concern in recent decades due to their significant impacts on the environment, health, agriculture, livelihoods, and the economy. The impacts are felt throughout the developed and developing world and their mitigation is aligned with several of the United Nations&#8217; Sustainable Development Goals. There has been an ever-increasing need for accurate information and predictions on SDS&#8212;particularly over desert regions such as the Sahara and in the Middle East&#8212;to support early warning systems as well as preparedness and mitigation plans, in addition to growing interest from diverse stakeholders and policymakers in the solar energy, health, environment and aviation sectors.&#160;The ongoing&#160;ERA4CS &#8216;Dust Storms Assessment for the development of user-oriented Climate services in Northern Africa, the Middle East and Europe&#8217; (DustClim)&#160;project is enhancing our knowledge of the ways SDS affect society by producing and delivering an advanced dust regional model reanalysis for N. Africa, the Middle East and Europe, based on the MONARCH chemical weather prediction system (P&#233;rez et al. 2011; Di Tomaso et al. 2017) and satellite retrievals over dust source regions, and by developing dust-related services tailored to strategic planning, operations, and policy-making in the air quality, aviation, and solar energy sectors. &#160;In this contribution, we will present how the resulting dust reanalysis is used as the basis to understand the mid-to-long-term impacts and implications of operating (and regulating) in risky sand and dust environments, namely: (1) the mineral dust component of air quality and its health and regulatory implications; (2) aircraft and airport operations, maintenance and planning; (3) strategic investment and operations optimization in solar energy. We will present our development approach that integrates scientific, industrial and regulatory knowledge, addressing &#8216;objective threats&#8217; in dialogue with industry partners and public stakeholders (Votsis et al. 2020). Finally, we present an overview of the developed portfolio of SDS climate services for the three aforementioned sectors.Acknowledgment The authors acknowledge DustClim project, part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Union (435690462); PRACE (eDUST, eFRAGMENT1, eFRAGMENT2); RES (AECT-2020-3-0013) for awarding access to MareNostrum at BSC and for technical support.ReferencesDi Tomaso, E. et al. (2017): Assimilation of MODIS Dark Target and Deep Blue observations in the dust aerosol component of NMMB-MONARCH version 1.0, Geosci. Model Dev., 10, 1107-1129, doi:10.5194/gmd-10-1107-2017.P&#233;rez, C. et al. (2011): An online mineral dust aerosol model for meso to global scales: Model description, annual simulations and evaluation, Atmos. Chem. Phys., 11, 13001-13027, doi: 10.5194/acp-11-13001-2011.Votsis, A. et al. (2020): Operational risks of sand and dust storms in aviation and solar energy: the DustClim approach, FMI's Climate Bulletin: Research Letters 1/2020, doi: 10.35614/ISSN-2341-6408-IK-2020-02-RL.

Science of The Total Environment, 2019

h i g h l i g h t s Meteorology, ship positioning and engine type influence the port role on near... more h i g h l i g h t s Meteorology, ship positioning and engine type influence the port role on nearby city air quality. The port activities contribute 33% of NO 2 43% of PM 10 and 60% of SO 2 causing no exceedance of the AQ limits Low Sulphur fuels do not prevent release of pollutants as ultra-fine particles, and black carbon. High loads of black carbon and ultrafine particles coexist with admitted loads of NO 2 , SO 2 , and PM.

Atmospheric Chemistry and Physics, Jan 3, 2017

Wildland fires represent the major source of accumulation mode aerosol (i.e., atmospheric particl... more Wildland fires represent the major source of accumulation mode aerosol (i.e., atmospheric particles with diameters <1 µm). The largest part of these fires occurs in Africa, Asia and South America, but a not negligible fraction also occurs in Eastern Europe and former USSR countries, particularly in the Russian Federation, Ukraine and Kazakhstan. Apart for exceptional cases as the Russian fires of summer 2010, routine agricultural fires in Eastern Europe and Russia have been recently shown to play a crucial role in the composition of the Arctic atmosphere. However, an evaluation of the impact of these fires over Europe is currently not available. The assessment of the relative contribution of fires to the European aerosol burden is hampered by the complex mixing of natural and anthropogenic particle types over the continent. In this study we use long term (2002-2007) satellite-based fires and aerosol data coupled to atmospheric transport modelling to attempt unravelling the wildfires contribution to the European aerosol optical thickness (AOT). Based on this dataset, we provide evidence that fires-related aerosol emissions play a major role in shaping the AOT yearly cycle at the continental scale. In general, the regions most impacted by wildfires emissions and/or transport are Eastern and Central Europe as well as Scandinavia. Conversely, a minor impact is found in Western Europe and Western Mediterranean. We estimate that in spring 5 to 35% of the European fine fraction AOT (FFAOT, i.e., the AOT due to accumulation mode particles) is attributable to wildland fires. The calculated impact maximizes in April (20-35%) in Eastern and Central Europe as well as in Scandinavia and in the Central Mediterranean. An important contribution of wildfires to FFAOT is also found in summer over most of the continent, particularly in August over Eastern Europe (28%) and the Mediterranean regions, from Turkey (34%) to the Western Mediterranean (25%). This unveiled, fires-related, continent-wide haze is expected to play a not negligible role on the European radiation budget, and possibly, on the European air quality, therefore representing a clear target for mitigation.

Atmospheric Chemistry and Physics, Mar 29, 2021

The impact of cloudiness and cloud type on the atmospheric heating rate 2 oktas, and up to 500 % ... more The impact of cloudiness and cloud type on the atmospheric heating rate 2 oktas, and up to 500 % in completely overcast conditions, 7-8 oktas). The impact of different cloud types on the HR was also investigated. Cirrus clouds were found to have a modest impact, decreasing the HR BC and HR BrC by −5 % at most. Cumulus clouds decreased the HR BC and HR BrC by −31 ± 12 % and −26 ± 7 %, respectively; cirrocumuluscirrostratus clouds decreased the HR BC and HR BrC by −60 ± 8 % and −54 ± 4 %, which was comparable to the impact of altocumulus (−60 ± 6 % and −46 ± 4 %). A higher impact on the HR BC and HR BrC suppression was found for stratocumulus (−63 ± 6 % and −58 ± 4 %, respectively) and altostratus (−78 ± 5 % and −73 ± 4 %, respectively). The highest impact was associated with stratus, suppressing the HR BC and HR BrC by −85 ± 5 % and −83 ± 3 %, respectively. The presence of clouds caused a decrease of both the HR BC and HR BrC (normalized to the absorption coefficient of the respective species) of −11.8 ± 1.2 % and −12.6 ± 1.4 % per okta. This study highlights the need to take into account the role of both cloudiness and different cloud types when estimating the HR caused by both BC and BrC and in turn decrease the uncertainties associated with the quantification of their impact on the climate.

&lt;p&gt;The impact of cloud fraction and cloud type on the heating rate (HR) of ... more &lt;p&gt;The impact of cloud fraction and cloud type on the heating rate (HR) of black and brown carbon (HR&lt;sub&gt;BC&lt;/sub&gt; and HR&lt;sub&gt;BrC&lt;/sub&gt;) was experimentally determined using a methodology developed in a previous study (Ferrero et al., 2018). High time-resolution measurements of the aerosol absorption coefficient at multiple-wavelengths (Aethalometer AE33 calibrated in COLOSSAL Campaign, Ferrero et al., 2021a) were coupled with spectral measurements of the direct, diffuse and surface reflected irradiance (Multiplexer-Radiometer-Irradiometer coupled with LSI-Lastem DPA154 and C201R, class 1 radiometers), and with lidar-ceilometer (Jenoptik Nimbus 15k biaxial lidar-ceilometer) during a one year field campaign in Milan, Po Valley (Italy).&lt;/p&gt;&lt;p&gt;The set-up allowed the experimental determination of the total HR (and its speciation: HR&lt;sub&gt;BC&lt;/sub&gt; and HR&lt;sub&gt;BrC&lt;/sub&gt;) in all sky conditions (from clear-sky to cloudy) with the highest total HR values found in the middle of winter (1.43&amp;#177;0.05 K day&lt;sup&gt;-1&lt;/sup&gt;). The HR&lt;sub&gt;BrC&lt;/sub&gt; accounted for 13.7&amp;#177;0.2% of the total HR (BrC absorption Angstrom exponent: 3.49&amp;#177;0.01).&lt;/p&gt;&lt;p&gt;Sky conditions were classified in terms of cloudiness (fraction of sky covered by clouds: oktas) and cloud types: stratus (St), cumulus (Cu), stratocumulus (Sc), altostratus (As), altocumulus (Ac), cirrus (Ci) and cirrocumulus-cirrostratus (Cc-Cs). During the campaign, clear sky conditions were present 23% of the time, the remaining time (77%) being characterized by cloudy conditions. The average cloudiness was 3.58&amp;#177;0.04 oktas (highest in February: 4.56&amp;#177;0.07 oktas, lowest in November: 2.91&amp;#177;0.06 oktas). St were mostly responsible of overcast conditions (oktas=7-8, frequency: 87 and 96%).&lt;/p&gt;&lt;p&gt;HR measurements showed a constant decrease with increasing cloudiness allowing to quantify the bias (in %) of the aerosol HR introduced by the simplified assumption of clear-sky conditions in radiative transfer model calculations. Results showed that the HR of light absorbing aerosol was ~20-30% lower in low cloudiness (oktas=1-2) up to 80% lower in complete overcast conditions (i.e., oktas=7-8), compared to clear sky ones. The impact of different cloud types on the HR was also investigated. Cirrus were found to have a modest impact, decreasing the HR&lt;sub&gt;BC&lt;/sub&gt; and HR&lt;sub&gt;BrC&lt;/sub&gt; by -5% at most. Cumulus decreased the HR&lt;sub&gt;BC&lt;/sub&gt; and HR&lt;sub&gt;BrC&lt;/sub&gt; by -31&amp;#177;12 and -26&amp;#177;7%, respectively; cirrocumulus-cirrostratus decreased the HR&lt;sub&gt;BC&lt;/sub&gt; and HR&lt;sub&gt;BrC&lt;/sub&gt; by -60&amp;#177;8 and -54&amp;#177;4%, which was comparable to the impact of altocumulus (-60&amp;#177;6 and -46&amp;#177;4%). A higher impact on HR&lt;sub&gt;BC&lt;/sub&gt; and HR&lt;sub&gt;BrC&lt;/sub&gt; suppression was found for stratocumulus (-63&amp;#177;6 and -58&amp;#177;4%, respectively) and altostratus (-78&amp;#177;5 and -73&amp;#177;4%, respectively). The highest impact was associated to stratus, suppressing the HR&lt;sub&gt;BC&lt;/sub&gt; and HR&lt;sub&gt;BrC&lt;/sub&gt; by -85&amp;#177;5 and -83&amp;#177;3%, respectively. The presence of clouds caused a decrease of both HR&lt;sub&gt;BC&lt;/sub&gt; and HR&lt;sub&gt;BrC&lt;/sub&gt; (normalized to the absorption coefficient of the respective species) of -11.8&amp;#177;1.2% and -12.6&amp;#177;1.4% per okta&amp;#160; (Ferrero et al., 2021b) allowing to parametrize the BC and BrC radiative impact in non clear sky conditions around the world.&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Ferrero L., et al., 2018. Environ. Sci. Tech., 52, 3546&amp;#8722;3555, DOI: 10.1021/acs.est.7b04320, 2018.&lt;/p&gt;&lt;p&gt;Ferrero, L., et al., 2021a. Science of the Total Environment 791. doi:10.1016/j.scitotenv.2021.148277.&lt;/p&gt;&lt;p&gt;Ferrero, L., et al. 2021b. Atmospheric Chemistry and Physics 21, 4869&amp;#8211;4897. doi:10.5194/acp-21-4869-2021.&lt;/p&gt;

Atmospheric Research, Dec 1, 2021

Abstract Parameterizations of the Planetary Boundary Layer (PBL) embedded in numerical weather pr... more Abstract Parameterizations of the Planetary Boundary Layer (PBL) embedded in numerical weather prediction models are crucial in the simulation of local meteorology and require a special investigation. In this study we evaluate simulations at 1 km horizontal resolution using six PBL schemes of the Weather Research and Forecasting model (WRF) by comparison to observations performed in a coastal port-industrial area (Civitavecchia) on the Tyrrhenian coast of Central Italy. During the measurement campaign (April 2016) three types of atmospheric circulation regimes were identified: “breeze”, “jet” and “synoptic”. Some generalizations can be inferred from the results, despite the variety of settings analyzed (two sites, three regimes in both day and night conditions). Our results show that the temperature simulation is much more sensitive to the configuration at night than during the day, especially on breeze days, when the occurrence of stable boundary layer is favored. For wind speed, non-local schemes are very similar to each other, unlike the local closure schemes. The use of the urban Building Environment Parameterization (BEP) significantly improves the simulation of the 2 m temperature during the “jet” evenings and nights, while it entails a further overestimation of the temperature during the “breeze” days leading to a reduction of the bias.