Anca Nemuc

Regularized inversion of microphysical atmospheric particle parameters: Theory and application

Retrieving the distribution of aerosols in the atmosphere via remote sensing techniques is a highly complex task that requires dealing with a wide range of different problems stemming both from Physics and Mathematics. We focus on retrieving this distribution from multi-wavelength lidar data for aerosol ensembles consisting of spherical particles via an iterative regularization technique. The optical efficiencies for spherical scatterers are examined to account for the behavior of the underlying integral equation. The ill-posedness of the problem and the conditioning of the discretized problem are analyzed. Some critical points in the model, like the assumed wavelength-independence of the refractive index and the fixed grid of investigated refractive indices, are studied with regard to their expected impact on the regularized solution. A new Monte-Carlo type method is proposed for retrieval of the refractive index. To validate the results, the developed algorithm is applied to two measurement cases of burning biomass gained from multi-wavelength Raman lidar.

Retrieval of the boundary layer height from active and passive remote sensors. Comparison with a NWP model

In this study, we used boundary layer heights derived from lidar in Romania to validate the Weather Research Forecast (WRF) model improved by ARIA Technologies SA in the framework of ROMAIR LIFE project. Lidar retrievals were also compared to the retrievals from meteorological data, both modeled (Global Data Assimilation System; GDAS) and measured (microwave radiometry). Both the gradient and the wavelet covariance methods were used to compute the boundary layer height (BLH) from the range corrected lidar signal, and their equivalence was shown.The analysis was performed on 102 datasets, spread over all seasons and 3 years (2009–2011). A good agreement was found for the remote sensors (lidar and microwave radiometer) which are co-located and measure simultaneously. The correlation of the measured boundary layer height and the modelled one was 0.66 for the entire dataset, and 0.73 when considering daytime data, i.e., for a well defined boundary layer. A systematic underestimation of the boundary layer height by the WRF during non-convective periods (nocturne, stable atmosphere) was found.

Mix of volcanic ash and Saharan dust over Romania during Eyjafjallajökull eruption

Located at a distance more than 3400Km from Iceland, where the eruption of Eyjafjallajökull volcano occurred, Romania was under the influence of volcanic ash transported by middle altitude air masses across Europe. Apart from two clear episodes on April 18 and April 21, 2010 the mix of volcanic ash with Saharan dust was detected by the multiwavelength Raman lidar in Bucharest. Optical properties of aerosol layers for these particular cases showed an increase of the linear particle depolarization, as well as a decrease of the Angstrom exponent, compared with the pure long-range transported volcanic ash. The case of May 5th, 2010 is analyzed from lidar and ground-level data, accounting for layer dynamics, optical properties and chemical composition. Using high resolution lidar data we could make a clear distinction between ash and dust layers up to their mixing in the PBL. In order to account for similarities and differences, the same analysis was done for May 10th and 11th, when several distinct layers were depicted. The signature of ash (sulfate) was identified by Aerosol Mass Spectrometer at ground-level, on May 5th and May 11th.

Corrigendum: Corrigendum to Regularized inversion of microphysical atmospheric particle parameters: Theory and application [J. Comput. Phys. 237 (2013) 79-94]

Abstract We correct typographical errors in our article [J. Comput. Phys. 237 (2013) 79–94].

Integrated E-System for Pollution and Climate Change Monitoring in the Framework of the Romanian Atmospheric Research 3D Observatory - RADO

The paper presents an overview on the implementation of integrated automated systems for pollution and climate change monitoring in the framework of RADO. RADOs mission is to improve modeling of physical, chemical, and biological processes, to assess the effects of climate change, and to quantify and reduce uncertainties in evaluating the hydrological cycle and its influence on natural resources. For this purpose, the integrated automated e-system, collecting data from different environmental monitoring instruments was developed.

Aerosol optical properties from multiwavelength lidar measurements in Romania

Vertically resolved profiles of optical properties of aerosols were measured using a multi-wavelength lidar system-RALI, set up at the scientific research center in Magurele, Bucharest area (44.35 N latitude, 26.03 E longitude) during 2008. The use of multiple laser wavelengths has enabled us to observe significant variations in backscatter profiles depending on the particle origins. An air mass backward trajectory analysis, using Hysplit-4, was carried out to track the aerosol plumes. Aerosols can serve as valuable tracers of air motion in the planetary boundary layer (PBL). The height of layers in the lower troposphere from lidar signal was calculated using the gradient method- minima of the first derivative. The Richardson number method was used to estimate PBL height from the radio-soundings. We have used pressure, temperature and dew point profiles as well as the wind direction profiles from NOAA (National Oceanic and Atmospheric Administration) data base. The results were consistent with the ones obtained from LIDAR.

Influence of urban aerosol pollution to radiative forcing

Daily PM10 concentrations of samples collected at two sites, urban and rural from Romania have been used to estimate the aerosol direct radiative forcing. Using OPAC (Optical Properties of Aerosols and Cloud) model we determined the single scattering albedo, the aerosol optical depth and aerosol up-scatter fraction, aerosols properties needed to estimate the magnitude and sign of direct aerosol radiative forcing. The surface albedo was assumed 0.2 for the urban site and 0.06 for the rural site for all wavelengths. For aerosol scale height we used 1km in winter and 2 km in the summer to calculate the optical depth of the boundary layer. Statistical analysis of the PM10 concentration for both sites show clear seasonal cycle with maxima in the winter. As a consequence of urban atmospheric pollution the radiative forcing for urban site appears strongly modified in comparison with rural site.

An Assessment of the Direct Radiative Forcing of the PM10-Study Case

Today the interest in aerosols is high mainly because of their effect on human health and their role in climate change. They have also a determining effect on visibility and contribute to the soiling of monuments. Observations and model calculations show that the increase in the atmospheric aerosol burden is delaying the global warming expected from the increase in greenhouse gasses (1). The aim of present paper is to analyze the direct effect of the aerosol and to compute the radiative forcing of the aerosol in different sites and meteorological conditions. The calculation of PM 10 levels and radiative forcing must necessarily be based on a description of the emissions of the individual chemical species and how they transform and mix in the atmosphere. We performed a statistical analysis of the emission of the aerosol for one year, amplitude of the concentrations and the temporal variability as is described in Section 1. The optical parameters and the equations used to compute the radiative forcing are presented in Section 2. Discussion of the results and a few concluding remarks are made in Section 3