Fábio J. S. Lopes

Study of the Properties of Aerosols and the Air Quality Index Using a Backscatter Lidar System and Aeronet Sunphotometer in the City of São Paulo, Brazil

Abstract Between the months of July and September of 2007 during the so-called Brazilian dry season, an aerosol profiling campaign was carried out with a backscatter(ing) lidar system in the city of São Paulo, Brazil. The main goal of this campaign was to observe the aerosol load in the troposphere (up to 10 km) and its daily behavior to check for air dispersion conditions, planetary boundary, and mixed layer height daily evolution. Lidar analysis provided aerosol optical properties in the visible range (532 nm) and quantities such as aerosol backscatter(ing) and extinction coefficients in conjunction with the aerosol optical thickness provided by a collocated AERONET Sunphotometer. Altogether 61 days were used in the dataset, which were compared with air quality indexation from the local air quality monitoring and management agency.

LALINET: The First Latin American–Born Regional Atmospheric Observational Network

AbstractSustained and coordinated efforts of lidar teams in Latin America at the beginning of the twenty-first century have built the Latin American Lidar Network (LALINET), the only observational network in Latin America created by the agreement and commitment of Latin American scientists. They worked with limited funding but an abundance of enthusiasm and commitment toward their joint goal. Before LALINET, there were a few pioneering lidar stations operating in Latin America, described briefly here. Biannual Latin American lidar workshops, held from 2001 to the present, supported both the development of the regional lidar community and LALINET. At those meetings, lidar researchers from Latin America met to conduct regular scientific and technical exchanges among themselves and with experts from the rest of the world. Regional and international scientific cooperation has played an important role in the development of both the individual teams and the network. The current LALINET status and activities are...

Lidar measurements of tropospheric aerosol and water vapor profiles during the winter season campaigns over the metropolitan area of Sao Paulo, Brazil

The so-called Metropolitan Area of São Paulo, one of the largest megacities in the world, faces several problems related to the air quality due the high concentrations of aerosols produced either by local sources or by long-range transporting. Concerned with the elevated concentrations of aerosol and their impact in the air quality and the climate changes inside MASP, a measurement campaign were conducted during the South hemisphere winter of 2012, when the low temperatures and the low level of precipitation contribute to the poor dispersion of aerosols. A Raman Lidar system and air quality monitoring stations from University of São Paulo and Environment Agency of São Paulo State (CETESB) were employed in order to monitor the increasing of aerosol load in the atmosphere. Satellite data, in synergy with HYSPLIT air masses backward trajectories, were applied to track the aerosol from the long-range distanced regions to Metropolitan Area of São Paulo. In the beginning of September 2012, MASP experienced episodes of high air pollution concentration, reaching Aerosol Optical Depth (AOD) values up to 0.89 at 550 nm and particulate matter concentration up to 293 µ g/cm3 . Particle lidar ratio values of 60 to 70 sr retrieved by a Raman Lidar system at 532 nm provided information of the aerosol type, helping to determine the influence of biomass burning advected from large range distance to megacities such as São Paulo

Comparison between two algorithms based on different wavelets to obtain the Planetary Boundary Layer height

Comprehension about the behavior of the Planet Boundary Layer (PBL) is an important factor in several fields, from analysis about air quality until modeling. However, monitoring the PBL evolution is a complex problem, because few instruments can provide continuous atmospheric measurements with enough spatial and temporal resolution. Inside this scenario lidar systems appear as an important tool, because it complies with all these capabilities- However, PBL observations are not a direct measure, being necessary to use complex mathematic algorithms. Recently, wavelet covariance transforms have been applied in this field. The objective of this work is to compare the performing of distinct types of algorithms: a structured on Haar wavelet and other based on first derivative of Gaussian and Mexican Hat wavelets, and the results were compared with two Hysplit modelling. For this aim, two campaigns were carried out. From the results were possible to infer that both algorithms provide coherent results as the expected, but the Haar algorithm separates the sub-layers more efficiently, so it is the most appropriate to complex situations.

Real-time mapping of an industrial flare using lidar

Characterization of atmospheric emissions from industrial flare stacks represents a challenge in measurement techniques because it is extremely difficult to determine the real-time concentrations of combustion products by in situ sampling, due to stack height, sensor calibration difficulties, and the dynamics of oscillations in the emission patterns. A ground based laser remote sensing (LIDAR) system has been developed for continuous and real-time monitoring of atmospheric emissions from an oil refinery located approximately 400 m from the instrument. The system is able to perform 3D scanning and profiling around the emission point. Tests were carried out using a scanning system pointed to the refinery flare. The mapping was obtained from a sequence of measurements at different zenithal and azimuthal angles resulting in a 3D image of the flare shape plus the flame itself. The measurements can be used to estimate the aerosol size distribution based on the ratios of the backscattering signal at three distinct wavelengths: 1064/532 nm, 1064/355 nm, and 532/355 nm. The method can be used in real time monitoring of industrial aerosol emissions and in the control of industrial processes. Preliminary results indicate a calibration procedure to assess the refining process efficiency based on the particle size distribution within and around the flare.

Sub-visual cirrus LIDAR measurements for satellite masking improvement

Understanding the impact of cirrus cloud on modifying both the solar reflected and terrestrial emitted radiations is crucial for climate studies. Unlike most boundary layer stratus and stratocumulus clouds that have a net cooling effect on the climate, high-level thin cirrus clouds have a warming effect on our climate. However, the satellites as GOES from the NOAA series are limited to the cloud top and its reflectivity or brightness temperature, without assessing accurately the optical depth or physical thickness. Other more recent sensors as MODIS are able to determine optical depths for aerosols and clouds but when related to cirrus they are still inaccurate. Research programs as First ISCCP, FIRE, HOIST, ECLIPS and ARM have concentrated efforts in the research of cirrus, being based mainly on the observations of combined terrestrial remote sensing and airplanes instruments. LIDARs are able to detect sub-visual cirrus cloud (SVCs) in altitudes above 15 km and estimate exactly their height, thickness and optical depth, contributing with information for satellites sensors and radiative transfer models. In order to research characteristics of SVCs, the LIDAR system at Instituto de Pesquisas Energeticas e Nucleares has as objective to determine such parameters and implement a cirrus cloud mask that could be used in the satellite images processing as well as in the qualitative improvement of the radiative parameters for numerical models of climate changes. The first preliminary study shows where we compare the data lidar with Brightness temperature differences between the split-window data from GOES-10 (DSA/INPE) and CALIPSO.

Molecular ordering of PAH/MA-co-DR13 azopolymer layer-by-layer films probed by second-harmonic generation

Molecular orientation within azopolymer thin films is important for their nonlinear optical properties and photonic applications. We have used optical second-harmonic generation (SHG) to study the molecular orientation of Layer-by-Layer (LbL) films of a cationic polyelectrolyte (poly(allylamine hydrochloride)) and an anionic polyelectrolyte containing azochromophore side groups (MA-co-DR13) on a glass substrate. The SHG measurements indicate that there is a preferential orientation of the azochromophores in the film, leading to a significant optical nonlinearity. However, both the signal strength and its anisotropy are not homogeneous throughout the sample, indicating the presence of large orientational domains. This is corroborated with Brewster angle microscopy. The average SHG signal does not increase with film thickness, in contrast to some reports in the literature, indicating an independent orientational order for successive bilayers. Analyzing the SHG signal as a function of the input and output polarizations, a few parameters of the azochromophore orientational distribution can be deduced. Fitting the SHG signal to a simple model distribution, we have concluded that the chromophores have an angular distribution with a slight in-plane anisotropy and a mean polar angle ranging from 45° to 80° with respect to substrate normal direction, with a relatively large width of about 25°. These results show that SHG is a powerful technique for a detailed investigation of the molecular orientation in azopolymer LbL films, allowing a deeper understanding of their self-assembling mechanism and nonlinear optical properties. The inhomogeneity and anisotropy of these films may have important consequences for their applications in nonlinear optical devices.

Automatic methods to detect the top of atmospheric boundary layer

The main objective of this work is to obtain methods that automatically allow qualitative detections of Atmospheric Boundary Layer heights from LIDAR data. Case studies will be used to describe the more relevant days of a campaign carried out in July of 2012 in Vitória, Espírito Santo, Brazil. The data analysis compares three mathematical algorithms that automatically provide the ABL height: Gradient Method (GM), using the derivative of the Range Corrected Signal (RCS) logarithm, WCT (Wavelet Covariance Transform), and Bulk Richardsons Number, which was used to validate the methods mentioned above. The comparison between the methods has shown that as the presence of clouds and the aerosol sublayer increased, the more sensitive was the refinement needed to choose the “right” parameters, whereas even Richardson’s method had ambiguities in finding a good estimate of the ABL top.

Indirect aerosol hygroscopic growth observations with a backscatter lidar

Aerosol Higroscopicity addresses a particular aspect of aerosol, namely, the extent to which they have an affinity for water vapor. The size increase of aerosol particles resulting from uptake of water vapor has important implications for the direct scattering of radiation and, under the right circumstances, to form cloud droplets. Ultimately this effect should have an important effect on the Earths radiative budget and belongs to a category well known as aerosol indirect effect. For this purposed we have used a single-wavelength backscatter LIDAR (532 nm), combined with thermodynamics considerations, to derivate the hygroscopic growing factor of aerosols over Sao Paulo metropolitan region. To test this factor assessment we employed data obtained in a single day, namely on 11 September 2007, when a well characterized humidity intrusion is onset due the transport of water vapor by a sea-breeze phenomenon. For this data, we calculated the backscatter coefficient at 532 nm, and used this parameter to obtain the hygroscopic growing factor, assuming a well-mixed boundary layer where a cloud cap condition is present or a well defined and pronounced mixing layer boundary are present and other thermodynamic assumptions. These assumptions guarantee that any changes in the backscatter coefficient are mainly due to changes in relative humidity, rather than in aerosol size distribution. The results shown here should be regarded as a first step on an ongoing monitoring process of aerosol growth factor and will in the near future be merged with a Water Vapor Raman Lidar system in order to have a simultaneous water vapor mixing ratio profile together with the aerosol profile and it should be mainly used when clear, low-aerosol load conditions are available.

Cloud-Aerosols interactions by multiple scenarios approach

Aerosols can play the role of cloud and ice condensation nuclei. This study shows a set of measurements and experiments analysis in remote sensing, in distinct scenarios of cloud cover during day/nightime measurements using lidar, visible all-sky camera and solar photometry. The retrieved products are studied to obtain aerosol optical and physical properties in the vicinity of clouds. In this approach cloud cover and optical properties should be retrieved as well main features used for cloud pixel identification, e. g., Red/Blue Difference, Red/Blue Ratio, Normalized Red/Blue Ratio, Saturation and Intensity. We show some case studies to illustrate this methodology.