Heterogeneity in aerosol characteristics at the semi-arid and island AERONET observing sites in India and Maldives

ABSTRACT

Multi-year Aerosol Robotic Network (AERONET) direct Sun retrieved and inversion algorithm derived aerosol products at a semi-arid, urban site, Jaipur (26.90° N, 75.80° E) and island observing site, Maldives Climate Observatory-Hanimaadhoo (MCO-Hanimaadhoo, 6.74° N, 73.17° E) are analysed to investigate heterogeneity in aerosol optical and microphysical properties. Results reveal the existence of a large seasonal diversity in the frequency distributions of aerosol optical depth (AOD_500 nm, AOD_1020 nm) and Ångström exponent (AE_{440–870 nm}) during different seasons at Jaipur and MCO-Hanimaadhoo. These are indicative of the advection of different aerosol types (viz., black carbon (BC) aerosol, organic aerosol, sulfate particle, dust, sea salt, nitrate particle, and mixtures thereof) from a variety of production mechanisms influenced by strong seasonal changes of anthropogenic activities as well as modulations induced by the climatic condition. The cumulative frequency analysis of the single scattering albedo (SSA) difference (i.e. ΔSSA = SSA_440 nm – SSA_1020 nm) shows that at Jaipur ΔSSA is predominantly negative (around 88% days) while at MCO-Hanimaadhoo it is positive (around 74% days). The positive and negative values of ΔSSA are respectively linked to a stronger absorption by BC mixed anthropogenic pollution aerosols at 1020 nm and to a stronger absorption by mineral dust containing iron oxide at 440 nm. The spectral behaviour of SSA, thus, facilitates investigation of the existence of iron oxide or BC in aerosols. The ‘Bivariate Kernel density’ plots of SSA versus fine-mode fraction (FMF) of AOD_440 nm/AE_{440–870 nm} reveal that at Jaipur the aerosol ensemble consists of coarse-mode particles (AE and FMF cluster in the range 0.2–0.4), a dominant category along with significant fine-mode and much less mixed category. At MCO-Hanimaadhoo fine-mode particle category (with FMF and AE cluster in the range 0.90–0.95 and 1.2–1.6 respectively) is the only dominant category. The persisting log-normal bimodal feature in aerosol volume size distribution (AVSD) is observed both at Jaipur and MCO-Hanimaadhoo. The modal volume concentration of coarse-mode aerosol decreases from FMF of AOD_675 nm = 0.25 (inherently belonging to the coarse-mode regime) to FMF of AOD_675 nm = 0.95 (inherently belonging to the fine-mode regime). This transformation in coarse-to fine-mode volume concentration is associated with a steady rise in AE_{440–874 nm} supporting this changeover.     

Effect of diethyl ether additive in Jatropha biodiesel-diesel fuel blends on the variable compression ratio diesel engine performance and emissions characteristics at different loads and compression ratios

An investigational analysis was performed to assess the effect of diethyl ether (DEE) that acts as an oxygenated additive in Jatropha biodiesel and diesel fuel blends on the performance enhancement and emission reduction of a variable compression ratio (CR) diesel engine. The DEE (10% vol) is added to different concentration levels of Jatropha biodiesel (B5, B10, and B20). The Jatropha biodiesel (JME) is prepared by the transesterification reaction and DEE is prepared through acid distillation of ethanol. The various tests were conducted by varying the loads at 25%, 50%, 75%, and 100% (3, 6, 9, and 12 kg). The DEE was entirely miscible with diesel and Jatropha biodiesel, the addition of DEE increases the cetane and calorific value, kinematic viscosity of the fuel blends compared with neat diesel or Jatropha biodiesel. The results illustrate that at higher loads and CRs, the engine performance parameters such as brake thermal efficiency enhances and reduces the brake-specific fuel consumption for DEE-Jatropha biodiesel-diesel fuel blends. Blend A3 (10% DEE + 20% JME + 70% diesel) demonstrated an overall improvement in the engine performance parameters and emission characteristics compared with A1, A2, and diesel fuel blends. It is concluded that the DEE-JME-diesel fuel blend is a promising source of fuel for diesel engine at maximum load.     

An investigation of temporal variability of the total column ozone over tropical urban,high altitude,and coastal stations in Western Maharashtra,India

Distribution and variability of ozone are vital to the atmospheric thermal structure as it can exert great influence on climate. In this study, the Microtops II Ozonometer (Microtops)-measured total column ozone (TCO) data archived at the tropical urban, high altitude, and coastal observing sites during 2012–2015 are analysed to investigate the temporal structure of ozone. Results reveal that the TCO exhibits a non-negligible diurnal variability depicting distinct seasonal behaviour, which corroborates well with the Indian as well as the worldwide measurements of TCO. The mean rate of ozone diurnal change (V_s) in winter is found to be maximum (approximately 2.1 DU h^–1) while it is minimum (about 0.53 DU h^–1) in pre-monsoon. In spite of the prevalent variability of the order of about 2–9 DU amongst Microtops channels and Ozone Monitoring Instrument on board the NASA EOS/AURA spacecraft (OMI-AURA) measurements, there exists a strong monthly/seasonal variation in both the ground- and satellite-based TCO measurements. Monthly mean OMI-AURA TCO variation presents a nearly perfect sinusoidal wave with a coefficient of determination (R²) equal to 0.76. Monthly TCO is maximum in May/June and minimum in December/January. The noticeable diurnal and monthly TCO variability could be due to a complex combination of photochemical processes in the lower troposphere and the transport in the middle and upper troposphere. Linear regression technique applied to the Microtops and OMI-AURA data sets show that the two data sets are better correlated with a correlation coefficient (r) taking values 0.71, 0.77, and 0.61 for channels I, II, and III, respectively. The three Microtops channels show the dispersion of about 8–11 DU around 1:1 regression line which is of the order of one standard deviation of the daily mean data set. The TCO data at all Microtops channels either underestimate or overestimate with respect to the OMI-AURA measurements since the values for slopes of the linear regression line for all the three channels are ≤1. Pearson’s product moment correlation analysis indicates that the TCO anti-correlates with ultraviolet-B (UV-B) irradiance (vis-à-vis through UV index) as the Pearson’s product moment correlation coefficients are found to be in the range –0.52 to –0.97.     

Classification of complex environments using pixel level fusion of satellite data

The present study reports classification and analysis of composite land features using fusion images obtained by fusing two original hyperspectral and multispectral datasets. The high spatial-spectral resolution, multi-instrument and multi-period satellite images were used for fusion. Three pixel level fusion based techniques, Color Normalized Spectral Sharpening (CNSS), Principal Component Spectral Sharpening Transform (PCSST) and Gram-Schmidt Transform (GST), were implemented on the datasets. Performance evaluations of three fusion algorithms were done using classification results. The Support Vector Machine (SVM) and Gaussian Maximum Likelihood Classification (MLC) were used for classification using five types of images, viz. hyperspectral, multispectral and three fused images. Number of classes considered was eight. Sufficient number of ground field data for each class has also been acquired which was needed for supervise based classification. The accuracy was improved from 74.44 to 97.65% when the fused images were considered with SVM classifier. Similarly, the results were improved from 69.25 to 94.61% with original and fused data using MLC classifier. The fusion image technique was found to be superior to the single original image and the SVM is better than the MLC method.

     

Organochlorines in antarctic and arctic avian top predators: a comparison between the South Polar Skua and two species of northern hemisphere gulls

Different organochlorine compounds (OCs) were measured in the blood of breeding south polar skuas (Catharacta maccormicki) at Svarthamaren, Dronning Maud Land (Antarctica) and compared to those in two species of northern hemisphere gulls: the Arctic glaucous gull (Larus hyperboreus) and the subarctic great black-backed gull (Larus marinus). The skuas had 8% and 29% of the SigmaOC levels (45 ng/g, wet weight) of glaucous gulls (591 ng/g) and great black-backed gulls (158 ng/g), respectively. Polychlorinated biphenyls (PCBs) and p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) were very low in skuas compared to northern gulls, but the mean hexachlorobenzene (HCB) level was 1.7 times higher than in great black-backed gulls and one-third of the glaucous gull level. Mirex levels in skuas were among the highest reported in birds, the mean level being 3 and 26 times higher than those in glaucous gull and great black-backed gulls, respectively. In skuas, the mean levels of HCB, oxychlordane, p,p'-DDE, and PCBs increased by about 30% during a 2-week period, and mirex increased by nearly 60%. In glacuous gulls, HCB, p,p'-DDE, and PCBs increased by 10-20%. For HCB, mirex, and oxychlordane, only a relatively small proportion of the increase in skuas could be explained by changes in lipid pools and the levels at first sampling, compared to glaucous gulls. Thus, skuas were probably accumulating these compounds when present in Antarctica. p,p'-DDE and PCB levels, in contrast, seemed much more stable in the skuas. Relatively high levels of mirex and HCB in south polar skuas are concerning with regard to potential adverse effects.