Wavelength Exponent Research Articles

Wavelength exponent based calibration for turbidity spectroscopy: Monitoring the particle size during emulsion polymerization reactions

Particle size and particle size distribution (PSD) are important properties of polymer latexes because they strongly affect the film formation and the rheological properties of the latexes. Thus, monitoring the particle size is of paramount importance during the production of waterborne polymeric dispersions, for which online/inline measurements of the particle size are required. Herein, turbidity spectroscopy (TUS) is used to measure the particle size of nanoparticles in dispersed media. Calibration curves based on a modified wavelength exponent method are introduced and assessed to monitor the evolution of a broad range of particle sizes in seeded semibatch emulsion polymerizations of methyl methacrylate, butyl acrylate, methacrylic acid (MMA/BA/MAA 51/47/2) terpolymers. It is shown that the wavelength exponent based calibration curves can be successfully used to retrieve the particle size during the polymerization process.

Variations of Aerosol Optical Depth in Bhaktapur, Nepal

The study is based on the variations of aerosol optical depth in Bhaktapur, Nepal. Microtops II Sunphotometer, manufactured by solar light inc. USA was used to measure the Aerosol optical depth. The diurnal variations of Aerosol Optical Depth (AOD) in January, 9 at 2.32UT were found to be 1.01, 0.89, 0.81 and 0.61 at 340,440, 500 and 675nm respectively. Besides ozone and clouds, aerosol plays an influencing role to attenuate solar UV radiation reaching the ground. Spectral dependence of AOD possesses higher values at shorter wavelengths and gradually decreases towards longer wavelengths in all seasons. The value of wavelength exponent (α) and aerosols concentration (β) on June 15 and July 25 at Kaushaltar were found to be 0.80, 0.56 and 0.45, 0.57 respectively.Journal of the Institute of Engineering, 2017, 13(1): 133-138

Adaptive inversion algorithm for [formula omitted] visibility lidar incorporating in situ Angstrom wavelength exponent

An eye-safe 1.5μm visibility lidar is presented in this work considering in situ particle size distribution, which can be deployed in crowded places like airports. In such a case, the measured extinction coefficient at 1.5μm should be converted to that at 0.55μm for visibility retrieval. Although several models have been established since 1962, the accurate wavelength conversion remains a challenge. An adaptive inversion algorithm for 1.5μm visibility lidar is proposed and demonstrated by using the in situ Angstrom wavelength exponent, which is derived from an aerosol spectrometer. The impact of the particle size distribution of atmospheric aerosols and the Rayleigh backscattering of atmospheric molecules are taken into account. Using the 1.5μm visibility lidar, the visibility with a temporal resolution of 5 min is detected over 48 h in Hefei (31.83∘N, 117.25∘E). The average visibility error between the new method and a visibility sensor (Vaisala, PWD52) is 5.2% with the R-square value of 0.96, while the relative error between another reference visibility lidar at 532 nm and the visibility sensor is 6.7% with the R-square value of 0.91. All results agree with each other well, demonstrating the accuracy and stability of the algorithm.

Scaling behavior of columnar structure during physical vapor deposition

The statistical effects of different conditions in physical vapor deposition, such as sputter deposition, have on thin film morphology has long been the subject of interest. One notable effect is that of column development due to differential chamber pressure in the well-known empirical model called the Thornton's Structure Zone Model. The model is qualitative in nature and theoretical understanding with quantitative predictions of the morphology is still lacking due, in part, to the absence of a quantitative description of the incident flux distribution on the growth front. In this work, we propose an incident Gaussian flux model developed from a series of binary hard-sphere collisions and simulate its effects using Monte Carlo methods and a solid-on-solid growth scheme. We also propose an approximate cosine-power distribution for faster Monte Carlo sampling. With this model, it is observed that higher chamber pressures widen the average deposition angle, and similarly increase the growth of column diameters (or lateral correlation length) and the column-to-column separation (film surface wavelength). We treat both the column diameter and the surface wavelength as power laws. It is seen that both the column diameter exponent and the wavelength exponent are very sensitive to changes in pressure for low pressures (0.13 Pa to 0.80 Pa); meanwhile, both exponents saturate for higher pressures (0.80 Pa to 6.7 Pa) around a value of 0.6. These predictions will serve as guides to future experiments for quantitative description of the film morphology under a wide range of vapor pressure.

Seasonal assessment and classification of aerosols transported to Lahore using AERONET and MODIS deep blue retrievals

ABSTRACTDaily measurements of aerosol optical depth (τ) and Ångstrom wavelength exponent (α) acquired from Aerosol Robotic Network (AERONET) and Moderate Resolution Imaging Spectrometer (MODIS) are analysed over Lahore – an urban city of Pakistan (period: 2010–2014) to investigate contribution of different types of aerosols originating from both local and regional source locations. The obtained annual averages (mean ± standard deviation) for AERONET retrievals of τ (500 nm) and α (440–870 nm) are 0.68 ± 0.37 (0.08–2.91) and 0.99 ± 0.33 (0–1.8), respectively. Of all the sources, 61% are found within Pakistan, 11% in India, 19% in Afghanistan, 6% in Iran and 2% in Saudi Arabia with seasonal contributions of 35, 25, 23 and 17% in pre‐monsoon, monsoon, winter and post‐monsoon, respectively. The bimodal distributions of α show dominance of coarse‐mode particles during pre‐monsoon, fine‐mode particles during post‐monsoon and presence of both coarse‐mode and fine‐mode particles during winter and monsoon with winter showing more fine‐mode particles. Two broad classes of aerosols namely desert dust (DD) and biomass burning/urban industrial (BU) are identified with criteria, e.g. τ ≥ 0.3 and α ≤ 0.75 indicating presence of DD while τ ≥ 0.2 and α ≥ 1.15 indicating BU. The frequency of occurrence (FOO) of DD and BU aerosols is further identified by applying classification criteria over Aqua‐MODIS deep blue retrievals. The FOO identifies anthropogenic activity on‐going throughout the year, disrupted with DD aerosols only during pre‐monsoon and monsoon. The maximum dust activity is seen over Indo‐Gangetic plains (IGP) (localized maxima: 35–45%) and the Arabian peninsula (>55%) during pre‐monsoon, while maximum BU aerosols are found over IGP, central and south‐eastern plains of India and the state of Gujarat (localized maxima: >70%) in winter and post‐monsoon.

Comparison of key absorption and optical properties between pure and transported anthropogenic dust over East and Central Asia

Abstract. Asian dust particulate is one of the primary aerosol constituents in the Earth–atmosphere system that exerts profound influences on environmental quality, human health, the marine biogeochemical cycle, and Earth's climate. To date, the absorptive capacity of dust aerosol generated from the Asian desert region is still an open question. In this article, we compile columnar key absorption and optical properties of mineral dust over East and Central Asian areas by utilizing the multiyear quality-assured datasets observed at 13 sites of the Aerosol Robotic Network (AERONET). We identify two types of Asian dust according to threshold criteria from previously published literature. (1) The particles with high aerosol optical depth at 440 nm (AOD440 ≥ 0.4) and a low Ångström wavelength exponent at 440–870 nm (α < 0.2) are defined as Pure Dust (PDU), which decreases disturbance of other non-dust aerosols and keeps high accuracy of pure Asian dust. (2) The particles with AOD440 ≥ 0.4 and 0.2 < α < 0.6 are designated as Transported Anthropogenic Dust (TDU), which is mainly dominated by dust aerosol and might mix with other anthropogenic aerosol types. Our results reveal that the primary components of high AOD days are predominantly dust over East and Central Asian regions, even if their variations rely on different sources, distance from the source, emission mechanisms, and meteorological characteristics. The overall mean and standard deviation of single-scattering albedo, asymmetry factor, real part and imaginary part of complex refractive index at 550 nm for Asian PDU are 0.935 ± 0.014, 0.742 ± 0.008, 1.526 ± 0.029, and 0.00226 ± 0.00056, respectively, while corresponding values are 0.921 ± 0.021, 0.723 ± 0.009, 1.521 ± 0.025, and 0.00364 ± 0.0014 for Asian TDU. Aerosol shortwave direct radiative effects at the top of the atmosphere (TOA), at the surface (SFC), and in the atmospheric layer (ATM) for Asian PDU (α < 0.2) and TDU (0.2 < α < 0.6) computed in this study, are a factor of 2 smaller than the results of Optical Properties of Aerosols and Clouds (OPAC) mineral-accumulated (mineral-acc.) and mineral-transported (mineral-tran.) modes. Therefore, we are convinced that our results hold promise for updating and improving accuracies of Asian dust characteristics in present-day remote sensing applications and regional or global climate models.

Continuous Monitoring of Metal Working Fluid Quality in Machining Processes

Metal working fluid (MWF) emulsions are utilized as coolants and lubricants in machining processes like turning or drilling. During their operation life time cycle, MWFs change their properties due to impacting stresses which may influence the machining and tool performance. A frequent refreshing or renewal of MWFs in machining process is thus necessary. This investigation discusses measurement techniques of MWF emulsions to be used for MWF quality assessment and process monitoring. By means of optical spectroscopic measurement techniques (turbidimetry and laser diffraction), the evaluation of the temporal change of the wavelength exponent and the MWF emulsion droplet size is related to the MWF stability. The in-process monitoring of the MWFs in machining during several weeks of operation is shown. Thus, it will be demonstrated that optical spectroscopic measurement techniques may be applied to determine stability change of the emulsion system.

Seasonal variation of vertical distribution of aerosol single scattering albedo over Indian sub-continent: RAWEX aircraft observations

To characterize the vertical distribution of aerosols and its seasonality (especially the single scattering albedo, SSA) extensive profiling of aerosol scattering and absorption coefficients have been carried out using an instrumented aircraft from seven base stations spread across the Indian mainland during winter 2012 and spring/pre-monsoon 2013 under the Regional Aerosol Warming Experiment (RAWEX). Spatial variation of the vertical profiles of the asymmetry parameter, the wavelength exponent of the absorption coefficient and the single scattering albedo, derived from the measurements, are used to infer the source characteristics of winter and pre-monsoon aerosols as well as the seasonality of free tropospheric aerosols. The relatively high value of the wavelength exponent of absorption coefficient over most of the regions indicates the contribution from biomass burning and dust aerosols up to lower free tropospheric altitudes. A clear enhancement in aerosol loading and its absorbing nature is seen at lower free troposphere levels (above the planetary boundary layer) over the entire mainland during spring/pre-monsoon season compared to winter, whereas concentration of aerosols within the boundary layer showed a decrease from winter to spring. This could have significant implications on the aerosol heating structure over the Indian region and hence the regional climate.

Seasonal variation and difference of aerosol optical properties in columnar and surface atmospheres over Shanghai

Abstract Aerosol optical properties in columnar and surface atmospheres were measured at an urban station of Shanghai from December 2010 to October 2012, and their seasonal variations and differences were examined. Aerosol optical thickness (AOT) at 500 nm is on average about 0.72 over the entire campaign, relatively higher in spring and summer and lower in autumn and winter. Angstrom wavelength exponent (Alfa) mainly distributes in 1.1–1.6 (72%) with an obvious uni-peak pattern, implying that fine particles are primary in the aerosol group. Aerosol single scattering albedo of columnar atmosphere (SSA) at 440 nm experiences a weak seasonal variation with an average of 0.91, indicating that aerosols are mainly composed of particles with relatively higher scattering efficiency. The aerosol volume size distribution shows one fine mode and another coarse mode, with peak radii of 0.15 μm and 3.0 μm, respectively. The volume of fine mode particles is minimum in spring and maximum in summer, while the volume of coarse mode particles is minimum in autumn and maximum in winter. The scattering coefficient (Sc) of aerosols in surface atmosphere is relatively higher in winter and spring, the absorptive coefficient (Ab) is higher in autumn and summer. The SSA of surface atmosphere (SSA-surf) at 532 nm varies weakly over time with a lower deviation, mostly scattering in the range of 0.8–0.95 (82%). Although the disconnection of aerosol properties between columnar and surface atmospheres exists, AOT and Alfa are correlated to some extent with PM2.5 and visibility. However, the difference of SSA and SSA-surf is remarkable about 0.1. Overall, fine particles are dominant in aerosols and contribute to AOT significantly in this city, and their difference between surface and columnar atmospheres is unignored.

Estimation of atmospheric turbidity and surface radiative parameters using broadband clear sky solar irradiance models in Rio de Janeiro-Brasil

The main goal of this paper is to estimate a set of optimal seasonal, daily, and hourly values of atmospheric turbidity and surface radiative parameters Angstrom’s turbidity coefficient (β), Angstrom’s wavelength exponent (α), aerosol single scattering albedo (ω o ), forward scatterance (F c ) and average surface albedo (ρ g ), using the Brute Force multidimensional minimization method to minimize the difference between measured and simulated solar irradiance components, expressed as cost functions. In order to simulate the components of short-wave solar irradiance (direct, diffuse and global) for clear sky conditions, incidents on a horizontal surface in the Metropolitan Area of Rio de Janeiro (MARJ), Brazil (22° 51′ 27″ S, 43° 13′ 58″ W), we use two parameterized broadband solar irradiance models, called CPCR2 and Iqbal C, based on synoptic information. The meteorological variables such as precipitable water (u w ) and ozone concentration (u o ) required by the broadband solar models were obtained from moderate-resolution imaging spectroradiometer (MODIS) sensor on Terra and Aqua NASA platforms. For the implementation and validation processes, we use global and diffuse solar irradiance data measured by the radiometric platform of LabMiM, located in the north area of the MARJ. The data were measured between the years 2010 and 2012 at 1-min intervals. The performance of solar irradiance models using optimal parameters was evaluated with several quantitative statistical indicators and a subset of measured solar irradiance data. Some daily results for Angstrom’s wavelength exponent α were compared with Angstrom’s parameter (440–870 nm) values obtained by aerosol robotic network (AERONET) for 11 days, showing an acceptable level of agreement. Results for Angstrom’s turbidity coefficient β, associated with the amount of aerosols in the atmosphere, show a seasonal pattern according with increased precipitation during summer months (December–February) in the MARJ.

Lidar observation of the 2011 Puyehue-Cordón Caulle volcanic aerosols at Lauder, New Zealand

Abstract. On 4 June 2011, the Puyehue-Cordón Caulle volcanic complex (40.6° S, 72.1° W) in Chile erupted violently and injected volcanic aerosols into the atmosphere. For the safety of civil aviation, continuous lidar observations were made at Lauder, New Zealand (45.0° S, 169.7° E), from 11 June through 6 July 2011. The purpose of our study is to quantify the influence of the volcanic ejections from large eruptions, and we use the data from the ground-based lidar observation. We analyzed lidar data at a wavelength of 532 nm and derived the backscattering ratio and depolarization ratio profiles. During June and July, within the altitude range of 10–15 km, the volcanic aerosols had high depolarization ratios (20–35%), an indication of non-spherical volcanic ash particles. The time series of the backscattering ratio during continuous observations had three peaks occurring at about 12-day intervals: 26.7 at 11.2 km on 11 June, 18.1 at 12.0 km on 23 June, and 5.3 at 11.1 km on 6 July. The optical depth of the volcanic aerosols was 0.45 on 11 June, when the continuous lidar observation started, 0.31 on 23 June, and 0.12 on 6 July. The depolarization ratio values remained high up to a month after the eruption, and the small wavelength exponent calculated from the backscattering coefficients at 532 nm and 1064 nm suggests that a major constituent of the volcanic aerosols was large, non-spherical particles. The presence of volcanic ash in the stratosphere might affect the error in Greenhouse gases Observing SATellite (GOSAT) XCO2 retrieval using the 1.6 μm band. We briefly discuss the influence of the increased aerosols on GOSAT products.

Scattering and absorption characteristics of atmospheric aerosols over a semi-urban coastal environment

The scattering and absorption components of Aerosol Optical Depth (AOD) over a semi-urban coastal location (12.81°N, 80.03°E) near the mega city Chennai in peninsular India are separated using the collocated measurements of Black Carbon concentration and Atmospheric Boundary Layer Height (ABLH) from ERA Interim Reanalysis data assuming that most of the BC is contained and homogeneously mixed in the ABL. It is found that the absorption component to scattering component ratio has a strong seasonal variation with a pronounced maximum in the South West (SW) monsoon season. This is indicative of more effective wet removal of scattering aerosols than absorbing (BC) aerosols. There could also be an effect due to preferential removal of large particles which would have a lower content of BC. The Angstrom wavelength exponent shows a minimum in the SW monsoon season, the minimum being more pronounced for the scattering aerosols implying relative dominance of coarse mode particles. Investigation of the effect of Relative Humidity on scattering and absorption components of AOD revealed that the BC (absorbing) aerosols are non-hydrophilic/not coated with hydrophilic substance.

Infrared lidar observations of stratospheric aerosols.

We observed the stratospheric aerosol layer at 34° north latitude with a photon-counting 1574 nm lidar on three occasions in 2011. During all of the observations, we also operated a nearby 523.5 nm micropulse lidar and acquired National Weather Service upper air data. We analyzed the lidar data to find scattering ratio profiles and the integrated aerosol backscatter at both wavelengths and then calculated the color ratio and wavelength exponent for lidar backscattering from the stratospheric aerosols. The visible-light integrated backscatter values of the layer were in the range 2.8-3.5×10⁻⁴ sr⁻¹ and the infrared integrated backscatter values ranged from 2.4 to 3.7×10⁻⁵ sr⁻¹. The wavelength exponent was determined to be 1.9±0.2.

Spectral aerosol optical depth prediction by some broadband models. Validation with AERONET observations

A comprehensive investigation on the performance of aerosol optical depth at 500 nm (AOD500) predictions using broadband physical and statistical models is detailed here. Seven simple models and one more complicated model were selected. A special database with more than 26 000 broadband (direct solar beam) and spectral (AODλ) instantaneous observations at clear solar disc during 10 years (2002-2011) at Toravere (Estonia) was compiled for the intercomparison. The database allows analysing the variability and climatological behaviour of several column parameters: coefficient of broadband transparency, precipitable water, AOD500, and the Angstrom wavelength exponent (α). A statistical AOD500 model is finally recommended. It uses only two input parameters: coefficient of column broadband transparency and precipitable water. Two models from the set enabled variation of Angstrom α. However, consideration of a priori known instantaneous α values did not improve predictions.

Turbidimetry for the stability evaluation of emulsions used in machining industry

Emulsified fluids are used in many industrial and consumer areas, for instance as products in the food or health industry as well as technical fluids in the machining industry. Metalworking fluids (MWF) are used as coolants and lubricants in metalworking processes. During their usage MWF emulsions may change their physical and chemical properties, which influences their performance and decrease the physical stability and therefore their lifetime. This article discusses results of turbidimetric spectra measurement of MWF emulsions to be used for process control, MWF quality monitoring and formulation purposes. Therefore, laboratory experiments have been carried out investigating the physical stability. Metal working emulsions have been treated and destabilised by different concentrations of salts. The destabilisation process was monitored by undiluted turbidity measurements and evaluated by the temporal change of the wavelength exponent. Thus, it was possible to determine specific conditions, for example a specific critical salt concentration for maintaining, stability of the MWF formulations.

Aerosol Optical Properties over South Asia from Ground-Based Observations and Remote Sensing: A Review

Seasonal and inter-annual variabilities in aerosol optical depth (AOD) andaerosol size distribution are investigated using ground-based measurements (sun photometersand sun/sky radiometers), and MODIS (MODerate Imaging Spectroradiometer) and MISR(Multiangle Imaging SpectroRadiometer) satellites over Ahmedabad, Gurushikhar, Karachi,Kanpur and Gandhi College in South Asia during 2006–2008. An analysis and a review onthe comparison between aerosol optical depths measured from ground-based observationsand remote sensing over South Asia is performed. Karachi and Ahmedabad AODs aretwo times higher than Gurushikhar, a high altitude remote site. AODs over Kanpur andGandhi College in the Indo-Gangetic basin are higher than those measured over Ahmedabad,Gurushikhar and Karachi. Summer monsoon AODs are higher over Ahmedabad andKarachi, while winter AODs are higher over Kanpur and Gandhi College. AOD ratio,ratio of AODs obtained at 0.38 μm and 0.87 μm, is higher during postmonsoon andwinter than premonsoon and monsoon ratio suggesting the abundance of fine mode aerosolsduring postmonsoon and winter. Monsoon AOD ratios are lowest owing to the dominanceof coarse mode (mainly sea salt) particles. Ångström wavelength exponent (α) duringpostmonsoon and winter are higher than that of premonsoon and monsoon values. Lower α values over Gurushikhar and Karachi indicate the dominance of coarse mode aerosols(dust in Gurushikhar, and dust and sea salt in Karachi). Dominance of fine mode aerosolsdue to anthropogenic activities give rise to higher α values over urban locations (e.g.,Ahmedabad and Kanpur). Comparison between ground-based and MODIS (Terra andAqua) retrieved AODs show that aerosol optical depths do not change significantly inan hour and much of the diurnal AOD variation is captured well by the two MODISinstruments. The temporal difference (about an hour) between the ground-based and remotesensing measurements contributes negligibly to the observed differences in AODs. Thedifferences between ground-based and remote sensing (MODIS and MISR) AODs vary onspatial scales. During the study period (2006–2008) MODIS underestimates AODs overwestern India by about 0.04, while over the Indo-Gangetic Plain MODIS overestimatesAOD by 0.06 in (Kanpur) and underestimates by 0.07 (Gandhi College) with respect toAODs measured by hand held sun photometer and Microtops sun photometer (Ahmedabadand Gurushikhar), and AERONET sun/sky radiometers (Karachi, Kanpur and GandhiCollege) respectively. During the same period MISR underestimates AODs in the rangeof 0.02–0.17 over Ahmedabad, Gurushikhar, Karachi and Kanpur, while in Gandhi CollegeMISR overestimates AOD by 0.2 when compared to ground-based AODs. Results on spatial,seasonal and inter-annual variations in aerosol characteristics will be useful in improving theaerosol retrieval algorithms in remote sensing, and in regional and global estimates of aerosolradiative forcing.

Temporal variation of aerosol optical depth and associated shortwave radiative forcing over a coastal site along the west coast of India

Optical characterization of aerosol was performed by assessing the columnar aerosol optical depth (AOD) and angstrom wavelength exponent (α) using data from the Microtops II Sunphotometer. The data were collected on cloud free days over Goa, a coastal site along the west coast of India, from January to December 2008. Along with the composite aerosol, the black carbon (BC) mass concentration from the Aethalometer was also analyzed. The AOD0.500μm and angstrom wavelength exponent (α) were in the range of 0.26 to 0.7 and 0.52 to 1.33, respectively, indicative of a significant seasonal shift in aerosol characteristics during the study period. The monthly mean AOD0.500μm exhibited a bi-modal distribution, with a primary peak in April (0.7) and a secondary peak in October (0.54), whereas the minimum of 0.26 was observed in May. The monthly mean BC mass concentration varied between 0.31μg/m3 and 4.5μg/m3, and the single scattering albedo (SSA), estimated using the OPAC model, ranged from 0.87 to 0.97. Modeled aerosol optical properties were used to estimate the direct aerosol shortwave radiative forcing (DASRF) in the wavelength range 0.25μm4.0μm. The monthly mean forcing at the surface, at the top of the atmosphere (TOA) and in the atmosphere varied between −14.1Wm−2 and −35.6Wm−2, −6.7Wm−2 and −13.4Wm−2 and 5.5Wm−2 to 22.5Wm−2, respectively. These results indicate that the annual SSA cycle in the atmosphere is regulated by BC (absorbing aerosol), resulting in a positive forcing; however, the surface forcing was governed by the natural aerosol scattering, which yielded a negative forcing. These two conditions neutralized, resulting in a negative forcing at the TOA that remains nearly constant throughout the year.

Analysis of variation trends and causes of aerosol optical depth in Shaanxi Province using MODIS data

The temporal and spatial variations and causes of aerosol optical depth (AOD) in Shaanxi Province were investigated based on the Moderate Resolution Imaging Spectroradiometer (MODIS) derived aerosol data for the period of March 2000–February 2012. The results showed that the distribution of aerosol was largely affected by topography and local economic activities. Heavy aerosol loading and increasing tendency in AOD was observed in Guanzhong, Hanzhong and Ankang basin, while a reverse tendency was revealed in most other regions. The spatial distribution of aerosol Angstrom wavelength exponent was predominantly related to vegetation coverage in Shaanxi. Airborne dust from ground is an important source of coarse mode aerosols. Vegetation improvement indicated by an increase in normalized difference vegetation index (NDVI) and a reduction in dust weather led to a gradual decrease in coarse mode AOD to the north of Qinling Mountains in Shaanxi, while anthropogenic activities led to an increase in fine mode AOD in other areas except those covered by forests. The main aerosol type gradually shifted to the urban industrial type in Shaanxi.

Dust events and their influence on aerosol optical properties over Jaipur in Northwestern India

In this study, we systematically document the link between dust episodes and local scale regional aerosol optical properties over Jaipur located in the vicinity of Thar Desert in the northwestern state of Rajasthan. The seasonal variation of AOT(500 nm) (aerosol optical thickness) shows high values (0.51 ± 0.18) during pre-monsoon (dust dominant) season while low values (0.36 ± 0.14) are exhibited during winter. The Ångström wavelength exponent has been found to exhibit low value (<0.25) indicating relative dominance of coarse-mode particles during pre-monsoon season. The AOT increased from 0.36 (Aprilmean) to 0.575 (May-June(mean)). Consequently, volume concentration range increases from April through May-June followed by a sharp decline in July during the first active phase of the monsoon. Significantly high dust storms were observed over Jaipur as indicated by high values of single scattering albedo (SSA(440 nm) = 0.89, SSA(675 nm) = 0.95, SSA870 nm = 0.97, SSA(1,020 nm) = 0.976) than the previously reported values over IGP region sites. The larger SSA values (more scattering aerosol), especially at longer wavelengths, is due to the abundant dust loading, and is attributed to the measurement site's proximity to the Thar Desert. The mean and standard deviation in SSA and asymmetry parameter during pre-monsoon season over Jaipur is 0.938 ± 0.023 and 0.712 ± 0.017 at 675 nm wavelength, respectively. Back-trajectory air mass simulations suggest Thar Desert in northwestern India as the primary source of high aerosols dust loading over Jaipur region as well as contribution by long-range transport from the Arabian Peninsula and Middle East gulf regions, during pre-monsoon season.

Diurnal Characteristics of Angstrom Turbidity Parameters Over Manila, Philippines

The diurnal variation of the aerosol optical depth (AOD) at 500nm wavelength and the Angstrom turbidity coefficients (α and β) were derived from direct beam measurements. Results of the measurements showed that the AOD, α, and β variations at different time intervals were mainly influenced by human activities and industrial operations as the day progressed. Hourly variability of AOD (in terms of percent departure from the daily mean) showed that it increases from morning and then reaches its maximum diversion from the mean (25%) at noontime (around 11 AM local time) and then slowly decreases in the afternoon. The wavelength exponent showed an almost similar pattern of diurnal variability as AOD. Its variation ranges at about 6 % above and below the average value of α. However β has a different pattern as compared to AOD and α. It consistently departs above the mean at around 20% in the morning and close to 30% below the mean in the afternoon. Daily values of AOD range from 0.545 to 2.174 with values frequently in the range of 0.5 to 1.5. Daily α was frequently around 1.75 but its values ranged from 0.502 to 3.236. This denoted that fine particles were dominating over coarse particles.