Realistic Aerosol Research Articles

A coupled atmospheric simulation chamber system for the production of realistic aerosols and preclinical model exposure

A coupled atmospheric simulation chamber system for the production of realistic aerosols and preclinical model exposure

A simple and realistic aerosol emission approach for use in the Thompson–Eidhammer microphysics scheme in the NOAA UFS Weather Model (version GSL global-24Feb2022)

Abstract. A physics suite under development at NOAA's Global Systems Laboratory (GSL) includes the aerosol-aware double-moment Thompson–Eidhammer microphysics (TH-E MP) scheme. This microphysics scheme uses two aerosol variables (concentrations of water-friendly aerosol (WFA) and ice-friendly aerosol (IFA) numbers) to include interactions with some of the physical processes. In the original implementation, WFA and IFA depended on emissions derived from climatologies. In our approach, using the Common Community Physics Package (CCPP), we embedded modules of sea-salt emissions, dust emissions, and biomass-burning emissions, as well as of anthropogenic aerosol emissions, into the Unified Forecast System (UFS) to provide realistic aerosol emissions for these two variables. This represents a very simple approach with no additional tracer variables and therefore very limited additional computing cost. We then evaluated a comparison of simulations using the original TH-E MP approach, which derives the two aerosol variables using empirical emission formulas from climatologies (CTL) and simulations that use the online emissions (EXP). Aerosol optical depth (AOD) was derived from the two variables and appears quite realistic in the runs with online emissions when compared to analyzed fields. We found less resolved precipitation over Europe and North America from the EXP run, which represents an improvement compared to observations. Also interesting are moderately increased aerosol concentrations over the Southern Ocean from the EXP run, which invigorate the development of cloud water and enhance the resolved precipitation in those areas. This study shows that a more realistic representation of aerosol emissions may be useful when using double-moment microphysics schemes.

10 Validation of an Aerosol Exposure-Air Liquid Interface (AE-ALI) System to Facilitate Realistic Hazard Identification of Nano-Sized Aerosols

Abstract To facilitate hazard characterisation for inhaled engineered nanomaterials we have established an aerosol exposure air-liquid-interface (AE-ALI) system, incorporating a Cultex RFSTM cell exposure system. While offering potential benefits in terms of more realistic aerosol exposure mode over traditional submerged in vitro models and being in-line with the principles of the 3Rs, (replace, reduce and refine animal use), detailed system characterisation is required to produce reliable and reproducible results. As such, this work looked to fully characterise our AE-ALI system with a view to optimising cell viability of system controls and deposition quantity, uniformity, and reproducibility for engineered nanomaterials. Using a nano-CeO2 aerosol, the effects of exposure conditions and system parameters (e.g. temperature, electrostatic precipitator voltage and airflow) on deposition efficiency, pattern and reproducibility were investigated using ICP-MS. While results showed that appropriate choice of operating parameters can produce broadly uniform deposition, reproducibility was low, and dose monitoring during exposures is recommended. After initial optimisation of the system for deposition, the effect of exposure duration, well size and flowrate on cellular responses (e.g. cytotoxicity (LDH) and selected gene expression (IL-8, CXCL1, HMOX1, SPP1) of system controls (H2O aerosol) was investigated using human lung alveolar (A549) and primary small airway epithelial cells. Results indicate that even after optimisation for cell health, the system itself is “toxic” to cells in comparison to incubator controls, with increasing effects observed with exposure duration meaning exposure durations must be minimised. Results from this study highlight the need for detailed characterisation of AE-ALI systems prior to use.

Uncovering the cytotoxic effects of air pollution with multi-modal imaging of in vitro respiratory models.

Annually, an estimated seven million deaths are linked to exposure to airborne pollutants. Despite extensive epidemiological evidence supporting clear associations between poor air quality and a range of short- and long-term health effects, there are considerable gaps in our understanding of the specific mechanisms by which pollutant exposure induces adverse biological responses at the cellular and tissue levels. The development of more complex, predictive, in vitro respiratory models, including two- and three-dimensional cell cultures, spheroids, organoids and tissue cultures, along with more realistic aerosol exposure systems, offers new opportunities to investigate the cytotoxic effects of airborne particulates under controlled laboratory conditions. Parallel advances in high-resolution microscopy have resulted in a range of in vitro imaging tools capable of visualizing and analysing biological systems across unprecedented scales of length, time and complexity. This article considers state-of-the-art in vitro respiratory models and aerosol exposure systems and how they can be interrogated using high-resolution microscopy techniques to investigate cell-pollutant interactions, from the uptake and trafficking of particles to structural and functional modification of subcellular organelles and cells. These data can provide a mechanistic basis from which to advance our understanding of the health effects of airborne particulate pollution and develop improved mitigation measures.

On the role of aerosols in the production of orographically-induced extreme rainfall in near-maritime environments

The present study aims at disentangling the role of marine aerosols in extreme precipitation events of orographic nature over near-maritime locations. Being the hazardous character of these events mainly associated to runoffs and river floodings, their destructive potential makes them subjects of special interest. In pursuit of a deep understanding on the development mechanisms of such events, this study reproduces the conditions and development of an event ranging from 20 to 27 of December 2009 that took place in Southern Spain. During this event, a series of Atlantic fronts swept the southernmost part of the Iberian Peninsula which, along with water vapor entrainment in the form of an atmospheric river, produced rainfall accumulations up to 900 mm in some specific mountainous locations. With this purpose, a number of simulations are conducted to study the microphysical processes and aerosol-cloud interactions governing the rain production. The WRF model is utilized with two different configurations of the Morrison double-moment microphysics scheme: (1) with prescribed type and concentrations of aerosols (PA); and (2) a setup in which a chemistry module is coupled to the meteorological core (Interactive Aerosols, IA), allowing for the consideration of prognostic aerosol concentrations and other relevant aspects such as the hygroscopicity and dry size of the different chemical species. According to the validation performed with a database constructed from measurements of rain gauges, results show that using prognostic aerosols concentrations for natural aerosols, namely sea salt and dust, improves the model's skill for reproducing extreme rainfall with respect to the setup using the default aerosols distribution prescribed in the WRF-alone simulations. Additionally, IA simulations increase windward precipitation and reduce leeward rainfall, thus largely amplifying the spatial variability of precipitation along the direction of the moisture flux. Besides, it is observed that this effect is independent of the model resolution. Consequently, it is concluded that a realistic aerosols concentration, along with a detailed treatment of both the size and hygroscopic properties of aerosols, have a crucial impact on the microphysical processes involved in this type of orographically-induced extreme precipitation events. Specifically, under a regime of low concentration of cloud condensation nuclei originating from natural aerosols, the formed cloud droplets are more prone to grow to precipitating size, thus enhancing the auto-conversion rate.

Combining POLDER-3 satellite observations and WRF-Chem numerical simulations to derive biomass burning aerosol properties over the southeast Atlantic region

Abstract. Aerosol absorption is a key property to assess the radiative impacts of aerosols on climate at both global and regional scales. The aerosol physico-chemical and optical properties remain not sufficiently constrained in climate models, with difficulties to properly represent both the aerosol load and their absorption properties in clear and cloudy scenes, especially for absorbing biomass burning aerosols (BBA). In this study we focus on biomass burning (BB) particle plumes transported above clouds over the southeast Atlantic (SEA) region off the southwest coast of Africa, in order to improve the representation of their physico-chemical and absorption properties. The methodology is based on aerosol regional numerical simulations from the WRF-Chem coupled meteorology–chemistry model combined with a detailed inventory of BB emissions and various sets of innovative aerosol remote sensing observations, both in clear and cloudy skies from the POLDER-3/PARASOL space sensor. Current literature indicates that some organic aerosol compounds (OC), called brown carbon (BrOC), primarily emitted by biomass combustion absorb the ultraviolet-blue radiation more efficiently than pure black carbon (BC). We exploit this specificity by comparing the spectral dependence of the aerosol single scattering albedo (SSA) derived from the POLDER-3 satellite observations in the 443–1020 nm wavelength range with the SSA simulated for different proportions of BC, OC and BrOC at the source level, considering the homogeneous internal mixing state of particles. These numerical simulation experiments are based on two main constraints: maintaining a realistic aerosol optical depth both in clear and above cloudy scenes and a realistic BC/OC mass ratio. Modelling experiments are presented and discussed to link the chemical composition with the absorption properties of BBA and to provide estimates of the relative proportions of black, organic and brown carbon in the African BBA plumes transported over the SEA region for July 2008. The absorbing fraction of organic aerosols in the BBA plumes, i.e. BrOC, is estimated at 2 % to 3 %. The simulated mean SSA are 0.81 (565 nm) and 0.84 (550 nm) in clear and above cloudy scenes respectively, in good agreement with those retrieved by POLDER-3 (0.85±0.05 at 565 nm in clear sky and at 550 nm above clouds) for the studied period.

Differential absorption lidar for water vapor isotopologues in the 1.98 µm spectral region: sensitivity analysis with respect to regional atmospheric variability

Abstract. Laser active remote sensing of tropospheric water vapor is a promising technology to complement passive observational means in order to enhance our understanding of processes governing the global hydrological cycle. In such a context, we investigate the potential of monitoring both water vapor H216O and its isotopologue HD16O using a differential absorption lidar (DIAL) allowing for ground-based remote measurements at high spatio-temporal resolution (150 m and 10 min) in the lower troposphere. This paper presents a sensitivity analysis and an error budget for a DIAL system under development which will operate in the 2 µm spectral region. Using a performance simulator, the sensitivity of the DIAL-retrieved mixing ratios to instrument-specific and environmental parameters is investigated. This numerical study uses different atmospheric conditions ranging from tropical to polar latitudes with realistic aerosol loads. Our simulations show that the measurement of the main isotopologue H216O is possible over the first 1.5 km of atmosphere with a relative precision in the water vapor mixing ratio of <1 % in a mid-latitude or tropical environment. For the measurement of HD16O mixing ratios under the same conditions, relative precision is found to be slightly lower but still sufficient for the retrieval of range-resolved isotopic ratios with precisions in δD of a few per mil. We also show that expected precisions vary by an order of magnitude between tropical and polar conditions, the latter giving rise to poorer sensitivity due to low water vapor content and low aerosol load. Such values have been obtained for a commercial InGaAs PIN photodiode, as well as for temporal and line-of-sight resolutions of 10 min and 150 m, respectively. Additionally, using vertical isotopologue profiles derived from a previous field campaign, precision estimates for the HD16O isotopic abundance are provided for that specific case.

Forcing Convection to Aggregate Using Diabatic Heating Perturbations.

Tropical deep convection can aggregate into large clusters, which can have impacts on the local humidity and precipitation. Sea surface temperature (SST) gradients have been shown to organize convection, yet there has been little work done to investigate the impact of diabatic heating perturbations in the atmosphere on the aggregation of convection. Here we investigate how anomalous diabatic heating of the atmospheric column, through an idealized aerosol plume, affects the existence and mechanisms of convective aggregation in non‐rotating, global radiative‐convective equilibrium simulations. We show that the aerosol forcing has the ability to increase the degree of aggregation, especially at lower SSTs. Detailed investigation shows that the diabatic heating source incites a thermally driven circulation, forced by the shortwave perturbation. The increase in aggregation is caused in part by this circulation, and in part by the longwave heating anomalies occurring due to the surface convergence of moisture and convection. At higher SSTs, longwave feedbacks are crucial for the aggregation of convection, even with the shortwave heating perturbation. At lower SSTs, convection is able to aggregate with the shortwave perturbation in the absence of longwave feedbacks. These perturbations provide a link to studying the effects of absorbing aerosol plumes on convection, for example during the Indian monsoon season. We argue that, as there is aggregation for plumes with realistic aerosol absorption optical depths, this could be an analogue for real‐world organization in regions with high pollution.

Improving WRF-Chem meteorological analyses and forecasts over aerosol polluted regions by incorporating NAAPS aerosol analyses

AbstractWhen unaccounted for in numerical weather prediction (NWP) models, heavy aerosol events can cause significant unrealized biases in forecasted meteorological parameters such as surface temperature. To improve near-surface forecasting accuracies during heavy aerosol loadings, we demonstrate the feasibility of incorporating aerosol fields from a global chemical transport model as initial and boundary conditions into a higher resolution NWP model with aerosol-meteorological coupling. This concept is tested for a major biomass burning smoke event over the Northern Great Plains region of the United States that occurred during summer of 2015. Aerosol analyses from the global Navy Aerosol Analysis and Prediction System (NAAPS) are used as initial and boundary conditions for Weather Research and Forecasting with Chemistry (WRF-Chem) simulations. Through incorporating more realistic aerosol direct effects into the WRF-Chem simulations, errors in WRF-Chem simulated surface downward shortwave radiative fluxes and near-surface temperature are reduced compared with surface-based observations. This study confirms the ability to decrease biases induced by the aerosol direct effect for regional NWP forecasts during high-impact aerosol episodes through the incorporation of analyses and forecasts from a global aerosol transport model.

Characterization of excipient enhanced growth (EEG) tobramycin dry powder aerosol formulations.

Spray drying can be utilized to produce highly dispersible powder aerosol formulations. However, these formulations are known to be hygroscopic, leading to potential solid-state stability and aerosol performance issues. This study aims to investigate if control of the spray drying particle formation conditions could be employed to improve the solid-state stability and alter the aerosol performance of tobramycin EEG formulations. Eight formulations were prepared, each had the same drug:excipient ratio of 60%w/w tobramycin, 20% w/w l-leucine, 18% w/w mannitol, and 2% w/w poloxamer 188. An experimental design matrix was performed with drying air water content of 1 or 10g/m3 and spray drying solution l-leucine concentrations of 4.6, 7.6, 15.2 or 23.0mmol/L. The particle size, morphology and crystallinity of spray dried formulations were characterized together with their dynamic moisture vapor sorption and aerosol performance. Higher crystallization and glass transition %RH were observed for the formulations spray dried using drying air with higher water content indicating more stable characteristics. Initial screening using a handheld dry powder inhaler of the realistic aerosol performance revealed that neither changing l-leucine concentration nor the drying gas water content affect the in-vitro expected lung dose. However, using a novel positive pressure inhaler, formulations produced using spray drying solutions with lower l-leucine concentrations showed better aerosol performance with MMAD around 2µm and FPF<5µm around 80%.

Validation and Accuracy Analysis of the Collection 6.1 MODIS Aerosol Optical Depth Over the Westernmost City in China Based on the Sun‐Sky Radiometer Observations From SONET

AbstractToward the Kashi region in northwest of China, the Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD) retrievals from Collection 6 (C6) MYD, Collection 6.1 (C6.1) MOD, and C6.1 MYD during 2016–2017 are compared with ground‐based measurements from the Sun‐sky Radiometer Network (SONET), and the first comprehensive evaluation of the Dark Target (DT) and Deep Blue (DB) retrievals with a 10‐km spatial resolution in the latest C6.1 MYD AOD data set during 2016–2018 is presented. In general, C6.1 MYD AOD products (both of DT and DB algorithm) are the most effective in Kashi of the three collections, and there is an overall underestimation of DB AOD, while DT AOD that slightly outperformed DB AOD in Kashi is overestimated on the whole. As to the factors that influence the accuracy of MODIS AOD, for DB algorithm, the overestimations of the surface reflectance and Single Scattering Albedo that DB aerosol model assumed can cause underestimation of DB AOD retrievals over Kashi, while the ones for DT algorithm are opposite. Besides, the coarse dust particles with lower veracity are predominant in Kashi region, which illustrated that the errors of particle size assumption in C6.1 MYD DT and DB algorithms will make large inversion error of MODIS AOD. Moreover, whatever DB or DT algorithm, the accuracy of AOD is diminished as the aerosol loading increases. The more realistic aerosol models and surface characterizations are necessary during the process of generating the MODIS aerosol retrievals in Kashi region.

Modeling of atmospheric dispersion of sodium fire aerosols for environmental impact analysis during accidental leaks

In this study a chemical kinetic model which converts sodium oxide aerosols to sodium carbonate aerosols as a function of CO2 and humidity is implemented in the FLEXPART atmospheric dispersion model for impact assessment during sodium fire accidents in sodium cooled fast reactors. The model is validated with open environment aerosol dispersion experiments conducted at Kalpakkam coastal site. Simulated total aerosol concentrations and deposition agree with experimental data. Simulations indicate rapid conversion of NaOH to Na2CO3 during atmospheric transport under high humidity levels (57–80%) at Kalpakkam. Parametric tests with different particle size indicated that a particle diameter of 5 μm produced realistic aerosol deposition closely comparing with observations. A series of simulations were conducted for various meteorological conditions to assess the chemical impact in a range of 25 km during a postulated accident. Simulations for extended 8-h release scenarios in different seasonal flow conditions indicate the concentrations beyond 1.5 km fall to very low values (≤0.1 mg/m3 for NaOH and ≤4 mg/m3 for Na2CO3) indicating no chemical impact. Short-duration (1 h) releases during worst environmental conditions (sea breeze, low winds) indicate that the aerosol concentrations during sea breeze are about 4–5 times high compared to winter time calm winds due to wide diffusion of aerosols in winter. The concentrations in these two cases are found to be higher (∼0.2 mg/m3 for NaOH and 6 mg/m3 for Na2CO3) in the site distance range but thereafter rapidly fall, thus indicating no inhalation hazard during sodium fire scenarios at the coastal site.

Aerosol Optical Depth from MODIS satellite data above the Pierre Auger Observatory

Aerosol optical depth can be retrieved from measurements performed by Moderate Resolution Imaging Spectroradiometer (MODIS) satellite instrument. The MODIS satellite system includes two polar satellites, Terra and Aqua. Each of them flies over the Pierre Auger Observatory once a day, providing two measurements of aerosols per day and covering the whole area of the Observatory. MODIS aerosol data products have been generated by three dedicated algorithms over bright and dark land and over ocean surface. We choose the Deep Blue algorithm data to investigate the distribution of aerosols over the Observatory, as this algorithm is the most appropriate one for semi-arid land of the Pierre Auger Observatory. This data algorithm allows us to obtain aerosol optical depth values for the investigated region, and to build cloud-free aerosol maps with a horizontal resolution 0.1°×0.1°. Since a suffcient number of measurements was obtained only for Loma Amarilla and Coihueco fluorescence detector (FD) sites of the Pierre Auger Observatory, a more detailed analysis of aerosol distributions is provided for these sites. Aerosols over these FD sites are generally distributed in a similar way each year, but some anomalies are also observed. These anomalies in aerosol distributions appear mainly due to some transient events, such as volcanic ash clouds, fires etc. We conclude that the Deep Blue MODIS algorithm provides more realistic aerosol optical depth values than other available algorithms.

Impacts of a newly-developed aerosol climatology on numerical weather prediction using a global atmospheric forecasting model

New four-dimensional aerosol climatology for global weather forecasting model is developed to take aerosol direct effect into account and its impacts on numerical weather prediction are investigated. The proposed aerosol climatology provides the global distribution of monthly-varying species-wise aerosol optical depths with more realistic aerosol vertical profiles. Including aerosol climatology enhances vertical stratification by surface cooling and atmospheric heating through the lower atmosphere by affecting radiation budget. Weakened vertical mixing and reduced surface fluxes related to aerosol loading result in decreased cloud fraction, particularly in the lower atmosphere. Evaluation of medium-range forecasts using the proposed aerosol climatology shows the overall improvement statistically for large-scale variable with reducing their biases, and the alleviation of systematic biases of overestimated light precipitation over the northern hemisphere.

Sensitivity of Homogeneous Ice Nucleation to Aerosol Perturbations and Its Implications for Aerosol Indirect Effects Through Cirrus Clouds

AbstractThe magnitude and sign of anthropogenic aerosol impacts on cirrus clouds through ice nucleation are still very uncertain. In this study, aerosol sensitivity (ηα), defined as the sensitivity of the number concentration (Ni) of ice crystals formed from homogeneous ice nucleation to aerosol number concentration (Na), is examined based on simulations from a cloud parcel model. The model represents the fundamental process of ice crystal formation that results from homogeneous nucleation. We find that the geometric dispersion (σ) of the aerosol size distribution used in the model is a key factor for ηα. For a monodisperse size distribution, ηα is close to zero in vertical updrafts (V &lt; 50 cm s−1) typical of cirrus clouds. However, ηα increases to 0.1–0.3 (i.e., Ni increases by a factor of 1.3–2.0 for a tenfold increase in Na) if aerosol particles follow lognormal size distributions with a σ of 1.6–2.3 in the upper troposphere. By varying the input aerosol and environmental parameters, our model reproduces a large range of ηα values derived from homogeneous ice nucleation parameterizations widely used in global climate models (GCMs). The differences in ηα from these parameterizations can translate into a range of anthropogenic aerosol longwave indirect forcings through cirrus clouds from 0.05 to 0.36 W m−2 with a GCM. Our study suggests that a larger ηα (0.1–0.3) is more plausible and the homogeneous nucleation parameterizations should include a realistic aerosol size distribution to accurately quantify anthropogenic aerosol indirect effects.

Quantifying the impact of early 21st century volcanic eruptions on global-mean surface temperature

Despite a continuous increase in well-mixed greenhouse gases, the global-mean surface temperature has shown a quasi-stabilization since 1998. This muted warming has been linked to the combined effects of internal climate variability and external forcing. The latter includes the impact of recent increase in the volcanic activity and of solar irradiance changes. Here we used a high-resolution coupled ocean–atmosphere climate model to assess the impact of the recent volcanic eruptions on the Earth's temperature, compared with the low volcanic activity of the early 2000s. Two sets of simulations are performed, one with realistic aerosol optical depth values, and the other with a fixed value of aerosol optical depth corresponding to a period of weak volcanic activity (1998–2002). We conclude that the observed recent increase in the volcanic activity led to a reduced warming trend (from 2003 to 2012) of 0.08 °C in ten years. The induced cooling is stronger during the last five-year period (2008–2012), with an annual global mean cooling of 0.04 °C (+/− 0.04 °C). The cooling is similar in summer (0.05 °C +/− 0.04 °C cooling) than in winter (0.03 °C +/− 0.04 °C cooling), but stronger in the Northern Hemisphere than in the Southern Hemisphere. Although equatorial and Arctic precipitation decreases in summer, the change in precipitation does not indicate robust changes at a local scale. Global heat content variations are found not to be impacted by the recent increase in volcanic activity.

Fast and slow shifts of the zonal‐mean intertropical convergence zone in response to an idealized anthropogenic aerosol

AbstractPrevious modeling work showed that aerosol can affect the position of the tropical rain belt, i.e., the intertropical convergence zone (ITCZ). Yet it remains unclear which aspects of the aerosol impact are robust across models, and which are not. Here we present simulations with seven comprehensive atmosphere models that study the fast and slow impacts of an idealized anthropogenic aerosol on the zonal‐mean ITCZ position. The fast impact, which results from aerosol atmospheric heating and land cooling before sea‐surface temperature (SST) has time to respond, causes a northward ITCZ shift. Yet the fast impact is compensated locally by decreased evaporation over the ocean, and a clear northward shift is only found for an unrealistically large aerosol forcing. The local compensation implies that while models differ in atmospheric aerosol heating, this does not contribute to model differences in the ITCZ shift. The slow impact includes the aerosol impact on the ocean surface energy balance and is mediated by SST changes. The slow impact is an order of magnitude more effective than the fast impact and causes a clear southward ITCZ shift for realistic aerosol forcing. Models agree well on the slow ITCZ shift when perturbed with the same SST pattern. However, an energetic analysis suggests that the slow ITCZ shifts would be substantially more model‐dependent in interactive‐SST setups due to model differences in clear‐sky radiative transfer and clouds. We also discuss implications for the representation of aerosol in climate models and attributions of recent observed ITCZ shifts to aerosol.

The Sensitivity of AOD Retrieval to Aerosol Type and Vertical Distribution over Land with MODIS Data

This study is to evaluate the sensitivity of Aerosol Optical Depth (AOD τ) to aerosol vertical profile and type, using the Moderate Resolution Imaging Spectroradiometer (MODIS) collection 6 algorithm over land. Four experiments were performed, using different aerosol properties including 3 possible non-dust aerosol models and 14 vertical distributions. The algorithm intrinsic uncertainty was investigated as well as the interplay effect of aerosol vertical profile and type on the retrieval. The results show that the AOD retrieval is highly sensitive to aerosol vertical profile and type. With 4 aerosol vertical distributions, the algorithm with a fixed vertical distribution gives about 5% error in the AOD retrieval with aerosol loading τ ≤ 0 . 5 . With pure aerosols (smoke and dust), the retrieval of AOD shows errors ranging from 2% to 30% for a series of vertical distributions. Errors in aerosol type assumption in the algorithm can lead to errors of up to 8% in the AOD retrieval. The interplay effect can give the AOD retrieval errors by over 6%. In addition, intrinsic algorithm errors were found, with a value of &gt;3% when τ&gt; 3.0. This is due to the incorrect estimation of the surface reflectance. The results suggest that the MODIS algorithm can be improved by considering a realistic aerosol model and its vertical profile, and even further improved by reducing the algorithm intrinsic errors.

Potential of polarization lidar to provide profiles of CCN- and INP-relevant aerosol parameters

Abstract. We investigate the potential of polarization lidar to provide vertical profiles of aerosol parameters from which cloud condensation nucleus (CCN) and ice nucleating particle (INP) number concentrations can be estimated. We show that height profiles of particle number concentrations n50, dry considering dry aerosol particles with radius &gt; 50 nm (reservoir of CCN in the case of marine and continental non-desert aerosols), n100, dry (particles with dry radius &gt; 100 nm, reservoir of desert dust CCN), and of n250, dry (particles with dry radius &gt; 250 nm, reservoir of favorable INP), as well as profiles of the particle surface area concentration sdry (used in INP parameterizations) can be retrieved from lidar-derived aerosol extinction coefficients σ with relative uncertainties of a factor of 1.5–2 in the case of n50, dry and n100, dry and of about 25–50 % in the case of n250, dry and sdry. Of key importance is the potential of polarization lidar to distinguish and separate the optical properties of desert aerosols from non-desert aerosol such as continental and marine particles. We investigate the relationship between σ, measured at ambient atmospheric conditions, and n50, dry for marine and continental aerosols, n100, dry for desert dust particles, and n250, dry and sdry for three aerosol types (desert, non-desert continental, marine) and for the main lidar wavelengths of 355, 532, and 1064 nm. Our study is based on multiyear Aerosol Robotic Network (AERONET) photometer observations of aerosol optical thickness and column-integrated particle size distribution at Leipzig, Germany, and Limassol, Cyprus, which cover all realistic aerosol mixtures. We further include AERONET data from field campaigns in Morocco, Cabo Verde, and Barbados, which provide pure dust and pure marine aerosol scenarios. By means of a simple CCN parameterization (with n50, dry or n100, dry as input) and available INP parameterization schemes (with n250, dry and sdry as input) we finally compute profiles of the CCN-relevant particle number concentration nCCN and the INP number concentration nINP. We apply the method to a lidar observation of a heavy dust outbreak crossing Cyprus and a case dominated by continental aerosol pollution.

Generation and Characterization of Indoor Fungal Aerosols for Inhalation Studies.

In the indoor environment, people are exposed to several fungal species. Evident dampness is associated with increased respiratory symptoms. To examine the immune responses associated with fungal exposure, mice are often exposed to a single species grown on an agar medium. The aim of this study was to develop an inhalation exposure system to be able to examine responses in mice exposed to mixed fungal species aerosolized from fungus-infested building materials. Indoor airborne fungi were sampled and cultivated on gypsum boards. Aerosols were characterized and compared with aerosols in homes. Aerosols containing 107 CFU of fungi/m3 air were generated repeatedly from fungus-infested gypsum boards in a mouse exposure chamber. Aerosols contained Aspergillus nidulans, Aspergillus niger, Aspergillus ustus, Aspergillus versicolor, Chaetomium globosum, Cladosporium herbarum, Penicillium brevicompactum, Penicillium camemberti, Penicillium chrysogenum, Penicillium commune, Penicillium glabrum, Penicillium olsonii, Penicillium rugulosum, Stachybotrys chartarum, and Wallemia sebi. They were all among the most abundant airborne species identified in 28 homes. Nine species from gypsum boards and 11 species in the homes are associated with water damage. Most fungi were present as single spores, but chains and clusters of different species and fragments were also present. The variation in exposure level during the 60 min of aerosol generation was similar to the variation measured in homes. Through aerosolization of fungi from the indoor environment, cultured on gypsum boards, it was possible to generate realistic aerosols in terms of species composition, concentration, and particle sizes. The inhalation-exposure system can be used to study responses to indoor fungi associated with water damage and the importance of fungal species composition.