Environmental pollution due to black carbon aerosols and its impacts in a tropical urban city

Black carbon (BC) has become the subject of interest in the recent years for a variety of reasons. BC aerosol may cause environmental as well as harmful health effects in densely inhabited regions. BC is a strong absorber of radiation in the visible and near-infrared part of the spectrum, where most of the solar energy is distributed. Black carbon is emitted into the atmosphere as a byproduct of all combustion processes, viz., vegetation burning, industrial effluents, motor vehicle exhausts, etc. In this paper, we present results from our measurements on BC aerosols, total aerosol mass concentration, and aerosol optical depth over an urban environment, namely Hyderabad during January-May, 2003. Diurnal variations of BC suggest that high BC concentrations are observed during 6:00-9:00 h and 19:00-23:00 h. Weekday variations of BC suggest that the day average BC concentrations increases gradually from Monday to Wednesday and gradually decreases from Thursday to Sunday. Fraction of BC to total mass concentration has been observed to be 7%. BC showed positive correlation with total mass concentration and aerosol optical depth at 500 nm. Radiative transfer calculations suggest that during January-May, diurnal averaged aerosol forcing at the surface was calculated to be −33 Wm⁻² and at the top of the atmosphere (TOA) it is to be +9 Wm⁻².     

Impact of aerosols on the forecast accuracy of solar irradiance calculated by a numerical weather prediction model

The impact of aerosols on the forecast accuracy of solar irradiance calculated by a fine-scale, one day-ahead, and operational numerical weather prediction model (NWP) is investigated in this study. In order to investigate the impact of aerosols only, the clear sky period is chosen, which is defined as when there are no clouds in the observation data and in the forecast data at the same time. The evaluation of the forecast accuracy of the solar irradiance is done at a single observation point that is sometimes affected by aerosol events. The analysis period is one year from April 2010 to March 2011. During the clear sky period, the root mean square errors (RMSE) of the global horizontal irradiance (GHI), direct normal irradiance (DNI), and diffuse horizontal irradiance (DHI) are 40.0?W?m^?2, 84.0?Wm^?2, and 47.9?W?m^?2, respectively. During one extreme event, the RMSEs of the GHI, DNI, and DHI are 70.1?W?m^?2, 211.6?W?m^?2, and 141.7?W?m^?2, respectively. It is revealed that the extreme events were caused by aerosols such as dust or haze. In order to investigate the impact of the aerosols, the sensitivity experiments of the aerosol optical depth (AOD) for the extreme events are executed. The best result is obtained by changing the AOD to 2.5 times the original AOD. This changed AOD is consistent with the satellite observation. Thus, it is our conclusion that an accurate aerosol forecast is important for the forecast accuracy of the solar irradiance.     

Dust aerosol forward scattering effects on ground-based aerosol optical depth retrievals

Monte Carlo radiative transfer calculations are performed to examine the forward scattering effects on retrievals of dust aerosol optical depth (AOD) from ground-based instruments. We consider dust aerosols with different AOD, effective radius and imaginary refractive index at 0.5 μm wavelength. The shape of dust aerosols is assumed to be spheroids and the equivalent spheres that preserve both volume and projected area (V/P) are also considered. The single-scattering albedos and asymmetry factors of spheroids and V/P-equivalent spheres have small differences, but the scattering phase functions are very different for the scattering angle range ∼90-180°. The relative errors of retrieved AOD caused by forward scattering effects due to the differences between the single-scattering properties of spheroids and spheres are similar. It is shown that at solar zenith angle (SZA) smaller than ∼70° the effect of the forward scattering is generally small although the relative errors in retrieved AOD can be as large as −10% when r_e=2. However, the largest relative errors, which can reach −40%, appear at high SZA (>∼70°) with AOD larger than 1. This is not caused by the increase of forward scattering intensity, but is due to the strong attenuation of solar direct beam.     

Assessment of the consistency of H2O line intensities over the near-infrared using sun-pointing ground-based Fourier transform spectroscopy

We report on the consistency of water vapour line intensities in selected spectral regions between 800-12,000 cm⁻¹ under atmospheric conditions using sun-pointing Fourier transform infrared spectroscopy. Measurements were made across a number of days at both a low and high altitude field site, sampling a relatively moist and relatively dry atmosphere. Our data suggests that across most of the 800-12,000 cm⁻¹ spectral region water vapour line intensities in recent spectral line databases are generally consistent with what was observed. However, we find that HITRAN-2008 water vapour line intensities are systematically lower by up to 20% in the 8000-9200 cm⁻¹ spectral interval relative to other spectral regions. This discrepancy is essentially removed when two new linelists (UCL08, a compilation of linelists and ab-initio calculations, and one based on recent laboratory measurements by Oudot et al. (2010) [10] in the 8000-9200 cm⁻¹ spectral region) are used. This strongly suggests that the H₂O line strengths in the HITRAN-2008 database are indeed underestimated in this spectral region and in need of revision. The calculated global-mean clear-sky absorption of solar radiation is increased by about 0.3 W m⁻² when using either the UCL08 or Oudot line parameters in the 8000-9200 cm⁻¹ region, instead of HITRAN-2008. We also found that the effect of isotopic fractionation of HDO is evident in the 2500-2900 cm⁻¹ region in the observations.     

Toward characterization of the aerosol optical properties over Loess Plateau of Northwestern China

Aerosol optical properties were obtained from a CIMEL sunphotometer of the Aerosol Robotic Network at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). SACOL is located over the Loess Plateau of the Northwestern China. The observed data are analyzed for the period of August 2006-October 2008. We find that aerosol optical depths (AODs) have a pronounced annual cycle, with a maximum dust aerosol loading during the spring. The 2-year average values of AOD, Ångström exponent (α), and water vapor path (WVP) along with their standard deviation (in parenthesis) are 0.35 (0.21), 0.93 (0.34), and 0.77 cm (0.52 cm), respectively. The probability distributions of these quantities all have one modal value, which are 0.3, 1.1, and 0.5 cm, respectively. There is a notable feature in the relationship between daily averaged AOD and Ångström exponent: a wide range of α corresponding to moderate to low aerosol optical depths (<0.8). There is no significant correlation between daily averaged WVP and AOD. However the daily averaged Ångström exponent and WVP show a significant positive correlation, indicating that the smaller aerosol particles present when the WVP is large. Variations of the retrieved aerosol volume size distributions are mainly associated with the changes in the concentration of the coarse aerosol fraction. The geometric mean radii for the fine and coarse aerosols are 0.18 μm (±0.03 μm), and 2.53 μm (±0.25 μm), respectively. The spectral dependences of the single scattering albedos are different between the dusty and non-dusty conditions. In the presence of dust, the SSAs increase slightly with wavelength. When dust is not a major component, the corresponding values decrease with wavelength.     

Seasonal variation of tropospheric aerosol properties by direct and scattered solar radiation spectroscopy

Long-term characterization of tropospheric aerosol has been carried out at Chiba, Japan, using a compact, stand-alone spectroradiometer under clear-sky conditions between August 2007 and March 2009. The spectra of direct solar radiation, aureole, and scattered solar radiation in various directions are observed in a wavelength range between 350 and 1050 nm with an optical resolution of 10 nm. Radiative transfer calculation using the MODTRAN4 code is employed to retrieve aerosol optical parameters such as aerosol optical depth (AOD), extinction coefficient, single-scattering albedo, scattering phase function, and asymmetry parameter, as well as water vapor column amount. The retrieved value of AOD varies in the range 0.1-0.5, while the water vapor column amount changes from 0.2 to 4 g/cm², showing reasonable agreements with the concurrent measurements with a sunphotometer and a microwave radiometer, respectively. The seasonal variation of the retrieved parameters indicates the major impacts of dust particles in spring, sea salt particles in summer, and anthropogenic fine particles in winter.     

Derivation of component aerosol direct radiative forcing at the top of atmosphere for clear-sky oceans

A two-step approach is proposed to derive component aerosol direct radiative forcing (ADRF) at the top of atmosphere (TOA) over global oceans from 60°S to 60°N for clear-sky condition by combining Terra CERES/MODIS-SSF shortwave (SW) flux and aerosol optical thickness (AOT) observations with the fractions of component AOTs from the GSFC/GOCART model. The derived global annual mean component ADRF is +0.08±0.17 W/m² for black carbon, −0.52±0.24 W/m² for organic carbon, −1.10±0.42 W/m² for sulfate, −0.99±0.37 W/m² for dust, −2.44±0.84 W/m² for sea salt, and −4.98±1.67 W/m² for total aerosols. The total ADRF has also been partitioned into anthropogenic and natural components with a value of −1.25±0.43 and −3.73±1.27 W/m², respectively. The major sources of error in the estimates have also been discussed. The analysis adds an alternative technique to narrow the large difference between current model-based and observation-based global estimates of component ADRF by combining the satellite measurement with the model simulation.     

Experimental intensity and lineshape parameters of the oxygen A-band using frequency-stabilized cavity ring-down spectroscopy

Line intensities, self- and air-broadened linewidths, pressure-induced shifts, and collisional narrowing coefficients were measured from 2 ? J′ ? 32 in the P branch of the O₂A-band (12 975-13110 cm⁻¹) utilizing Galatry line profiles. Spectra were recorded using the frequency-stabilized cavity ring-down spectrometer located at NIST, Gaithersburg, MD with a spectral resolution <0.0001 cm⁻¹ and noise-equivalent absorption coefficient of 6 × 10⁻⁸ m⁻¹ Hz^−1/2. Line intensities, obtained from calibrated gas samples for 2 ? J′ ? 32, are ∼1% lower than the values in current spectroscopic databases. At higher J (18 ? J′ ? 32), the measured air- and self- broadened half widths are up to 20% lower than the extrapolated values given in HITRAN 2004, while corresponding half-widths for 2 ? J′ ? 15 are in better agreement. Available self-broadened half widths are fitted to empirical expressions with an rms of 0.8%. We discuss the implications of our results for accurate remote sensing of surface pressure and photon path length distributions.     

Off-axis integrated cavity output spectroscopy and its application

Based upon the property of optical cavity and the principle of signals and systems, the measural theory and signal expression of off-axis integrated cavity output spectroscopy (Off-axis ICOS) have been analyzed and deduced. A compact and low-cost Off-axis ICOS apparatus, which used a special circuit to integrate the cavity output signal, was then described and experimented. The absorption spectrum of water vapor in the spectral range of 6587∼6595.5 cm⁻¹ was measured with this Off-axis ICOS system, and the measured spectral parameters were compared with the results of continuous-wave cavity ring down spectroscopy (CW-CRDS) and HITRAN2004 database. The detectable sensitivity of the system was achieved as ∼2.8 × 10⁻⁹ cm⁻¹.     

Microgravimetric and voltammetric study of Zn underpotential deposition on platinum in alkaline medium

The microgravimetric and voltammetric responses of a polycrystalline Pt electrode in 0.1 mol L⁻¹ NaOH solution in the presence and the absence of 1.6 × 10⁻⁴ Zn²⁺, at 0.1 V s⁻¹ were analyzed. During the positive potential sweep, the water molecules are progressively substituted by OH⁻ ions, prior to PtO formation. The voltammetric charges obtained under the Zn_ads dissolution peaks suggest that 0.7 monolayers are deposited, with each Zn ad-atom occupying one active site and transferring two electrons. The total loss of mass due to the dissolution of the Zn ad-layer was 136.6 ng cm⁻² and the mass increase due to PtO formation was found to be only 12 ng cm⁻² less than the theoretical ones, 157.5 and 37.4 ng cm⁻², respectively, indicating that both processes are overlapped. In this way it is proposed that an adsorbed by-layer of Zn and OH⁻ ions is formed.     

Carbon monoxide laser emitting nanosecond pulses with 10 MHz repetition rate

Actively mode-locked electron-beam-sustained-discharge CO laser producing a train of ∼5-15 ns (FWHM) spikes following with repetition rate 10 MHz for both single-line and multiline mode of operation in the mid-IR range of ∼5 μm was experimentally studied. Total laser pulse duration was ∼0.5 ms for both mode-locked and free-running laser. Specific output energy in multiline CO laser mode of operation was up to 20 Jl⁻¹ Amagat⁻¹ and the laser efficiency up to 3.5%. The active mode-locking was achieved for single-line CO laser mode of operation in spectral range 5.2-5.3 μm. This sort of radiation can be used for pumping an optical parametric amplifier for optical stochastic cooling in relativistic heavy ion collider, for laser ablation, and for studying vibrational and rotational relaxation of CO and NO molecules.     

Thermoelectric properties of sol-gel derived cobaltite Bi2Ca2.4Co2Oy

Layered misfit cobaltite Bi₂Ca_2.4Co₂O_y has been synthesized by a sol-gel method. This compound exhibits large thermoelectric (TE) power (S_300 K∼170 μV K⁻¹), low resistivity (ρ_300 K∼42 mΩ cm) and relatively small thermal conductivity (κ_300 K∼2.8 W K⁻¹ m⁻¹) at room temperature. Furthermore, the resistivity of this compound displays a metallic behavior above T^?∼150 K with a semiconducting behavior below this temperature. This abnormal behavior in resistivity is analogous to those observed in Sr and Ba based misfit cobaltites. The observed features of the TE have been discussed based on the narrow band model.     

Studies on CdTe films deposited by pulsed laser deposition technique

Polycrystalline cadmium telluride films were successfully deposited on glass substrates by ablating a CdTe target by pulsed Nd–YAG laser. Microstructural studies indicated an increase in the average crystallite size from 15 nm to ∼50 nm with the increase in substrate temperature during deposition. The films deposited here were slightly tellurium rich. X-ray diffraction pattern indicated that the films deposited at 300 K had wurtzite structure while those deposited above 573 K were predominantly of zinc blende structure. Residual strain in the films deposited at 300 K was quite low as compared to those deposited at higher temperatures. PL spectra of all the CdTe films were dominated by a strong peak at ∼921 nm (∼1.347 eV) followed by a low intensity peak at ∼863 nm (∼1.438 eV). Characteristics Raman peaks for CdTe indicated a peak at ∼120 cm⁻¹ followed by peaks located at ∼140 cm⁻¹ and 160 cm⁻¹.     

The electrodeposition behaviors and magnetic properties of Ni-Co films

Ni-Co films with different compositions and microstructures were produced on ITO glasses by electrodeposition from sulphate bath at 25 °C. Cyclic voltammograms give a result that the increase in the Co²⁺ concentration displaces Ni-Co alloy oxidation peaks to negative potential with high Co current distributions. It is observed that the content of cobalt in the films increases from 22.42% to 56.09% as the molar ratio of CoSO₄/NiSO₄ varying from 0.015/0.085 to 0.045/0.055 in electrolyte. XRD patterns reveal that the structure of the films strongly depends on the Co content in the deposited films. The saturation magnetization (M_s) moves up from 144.84 kA m⁻¹ to 342.35 kA m⁻¹ and coercivity (H_c) falls from 15.27 kA m⁻¹ to 7.27 kA m⁻¹ with the heat treatment temperature increasing from 25 °C to 450 °C. The saturation magnetization (M_s) and coercivity (H_c) move up from 340.97 kA m⁻¹ and 7.98 kA m⁻¹ to 971.58 kA m⁻¹ and 18.62 kA m⁻¹ with the Co content increasing from 22.42% to 56.09% after annealing at 450.     

Calculation of solar radiation atmospheric absorption with different H2O spectral line data banks

A comparison of the atmospheric absorption calculated with different data banks of water vapour absorption lines is made. The HITRAN database, Barber-Tennyson line list (BT2), calculation of Partridge and Schwenke (PS) are considered. The contribution of H₂O lines, absent in HITRAN, to the atmospheric transmission, calculated with 10 cm⁻¹ spectral resolution in the 10 000-20 000 cm⁻¹ spectral region is up to 1.5% for a vertical path and 4% for a solar zenith angle of 70 deg. The highest difference is observed in the 940 nm band. The incoming fluxes of solar radiation, measured by a rotating solar spectroradiometer, were modeled with BT2 and HITRAN database. The difference between measured and calculated fluxes does not exceed the instrumental uncertainties.     

Fluorescence and persistent spectral hole burning of Eu in Ge-Ga-S-KBr glasses

Fluorescence and efficient persistent spectral hole burning of Eu³⁺ at 77 K were observed in chalcohalide glasses. The depth of the hole was approximately 30% after a burning process of 1 min with 50 mW power, and it was completely erased with Ar⁺ laser irradiation. The hole survived room temperature heat treatment and showed good thermal stability. The hole-burning mechanism was most probably the photo-reduction of Eu³⁺→Eu²⁺. Fluorescence from Eu³⁺ decreased with increasing temperature and disappeared at the temperature above ∼130 K.     

The spectral sensitivity of long period gratings fabricated in elliptical core D-shaped optical fibre

Long period gratings (LPGs) were written into a D-shaped optical fibre that has an elliptical core with a W-shaped refractive index profile and the first detailed investigation of such LPGs is presented. The LPGs’ attenuation bands were found to be sensitive to the polarisation of the interrogating light with a spectral separation of about 15 nm between the two orthogonal polarisation states. A finite element method was successfully used to model many of the behavioural features of the LPGs. In addition, two spectrally overlapping attenuation bands corresponding to orthogonal polarisation states were observed; modelling successfully reproduced this spectral feature. The spectral sensitivity of both orthogonal states was experimentally measured with respect to temperature and bending. These LPG devices produced blue and red wavelength shifts depending upon the orientation of the bend with measured maximum sensitivities of −3.56 and +6.51 nm m, suggesting that this type of fibre LPG may be useful as a shape/bend orientation sensor with reduced errors associated with polarisation dependence. The use of neighbouring bands to discriminate between temperature and bending was also demonstrated, leading to an overall curvature error of ±0.14 m⁻¹ and an overall temperature error of ±0.3 °C with a maximum polarisation dependence error of ±8 × 10⁻² m⁻¹ for curvature and ±5 × 10⁻² °C for temperature.     

One-magnon light scattering and spin-reorientation transition in epitaxial BiFeO3 thin films

Raman scattering from one-magnon excitation has been observed for the first time in epitaxial BiFeO₃ thin films grown on (1 1 1) SrTiO₃ substrates. The intensities and the frequency of the magnon mode at 18.9 cm⁻¹ (M₁) showed a discrepancy at the characteristic temperatures of ∼140 and 200 K and the magnon mode at 27.9 cm⁻¹ (M₂) disappeared at ∼200 K suggesting spin-reorientation (SR) transition in the epitaxial BFO film. The dc susceptibility measurement showed a large discrepancy near these two temperatures evidently elucidating the spin-reorientation transition mechanism. The partial spectral weight of the magnon modes is believed to be transferred to the lowest phonon mode appearing at 72.8 cm⁻¹ and higher magnon mode M₂ disappearing near 200 K reveal magnon-phonon coupling near to SR transition.     

NO fundamental and first hot ro-vibrational line frequencies from MIPAS/Envisat atmospheric spectra

MIPAS (Michelson Interferometer for Passive Atmosphere Sounding) is a high spectral resolution interferometer (0.035 cm⁻¹ unapodized) covering a very wide spectral range (from 4.16 to 16.4 μm) with high sensitivity that was successfully launched on the 1st of March 2002 on the European Envisat satellite. MIPAS has measured spectra of the Earth’s upper atmosphere in the 4.3 μm region with the highest spectral resolution so far reached in this altitude region. This high spectral resolution permitted to obtain the frequency position of ro-vibrational NO⁺ transitions with an unprecedented accuracy. It has been found that the spectral line positions of the NO⁺ (1-0) ro-vibrational band are shifted by about ∼0.15 cm⁻¹ with respect to those listed in the HITRAN 2004 compilation. Also, spectral line positions of the NO⁺ (2-1) ro-vibrational band are shifted by approximately 0.05-0.1 cm⁻¹ with respect to those listed in the HITRAN 2004 compilation. A new set of Hamiltonian constants for NO⁺ has been derived from MIPAS data which is suggested to be used in future HITRAN compilations.     

Characterization of ?ngstr?m''s turbidity parameters in the Po Valley area for summer conditions of the atmosphere

Summary Measurements of direct solar irradiance were taken at the San Pietro Capofiume station in the centre of the Po Valley using two examples of the multispectral sun photometer, model UVISIR, on several clear-sky days of late spring and early summer in the years 1989 and 1990. Realistic evaluations of aerosol optical thickness at several sun-photometric wavelengths were obtained from these measurements by i) using values of the calibration constants carefully found by following both the Langley plot method and the spectral-correction procedure, which had previously been applied with satisfactory results to the sun-photometric measurements carried out in Antarctica and ii) taking into account the extinction effects produced by Rayleigh scattering and absorption due to ozone, water vapour and nitrogen dioxide on the solar radiation passing through the atmosphere. By examining a wide set of spectral series of the aerosol optical thickness in terms of the well-known Ångstr?m formula, a large number of pairs of atmospheric-turbidity parameters α and β was obtained, presenting a range of the mean daily values of α from 1.0 to 1.7 (with the median of 1.48) and a range of the mean daily values of β from 0.10 to 0.30 (with the median of 0.15). Using the particulate extinction models CR (for continental particles) and TR (for small tropospheric particles and large rural particles), the aerosol mass loading of the atmosphere calculated for these values of α and β was estimated to vary between 0.09 and 0.31 g m⁻² (with the median of 0.21 g m⁻²) during the measurement period of 1989 and between 0.09 and 0.41 g m⁻² (with the median of 0.13 g m⁻² for model CR and of 0.21 g m⁻² for model TR) during June and July 1990. Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.