Sharad Gokhale

Source apportionment of human personal exposure to volatile organic compounds in homes, offices and outdoors by chemical mass balance and genetic algorithm receptor models.

A number of past studies have shown the prevalence of a considerable amount of volatile organic compounds (VOCs) in workplace, home and outdoor microenvironments. The quantification of an individuals personal exposure to VOCs in each of these microenvironments is an essential task to recognize the health risks. In this paper, such a study of source apportionment of the human exposure to VOCs in homes, offices, and outdoors has been presented. Air samples, analysed for 25 organic compounds and sampled during one week in homes, offices, outdoors and close to persons, at seven locations in the city of Leipzig, have been utilized to recognize the concentration pattern of VOCs using the chemical mass balance (CMB) receptor model. In result, the largest contribution of VOCs to the personal exposure is from homes in the range of 42 to 73%, followed by outdoors, 18 to 34%, and the offices, 2 to 38% with the corresponding concentration ranges of 35 to 80 microg m(- 3), 10 to 45 microg m(- 3) and 1 to 30 microg m(- 3) respectively. The species such as benzene, dodecane, decane, methyl-cyclopentane, triethyltoluene and trichloroethylene dominate outdoors; methyl-cyclohexane, triethyltoluene, nonane, octane, tetraethyltoluene, undecane are highest in the offices; while, from the terpenoid group like 3-carane, limonene, a-pinene, b-pinene and the aromatics toluene and styrene most influence the homes. A genetic algorithm (GA) model has also been applied to carry out the source apportionment. Its results are comparable with that of CMB.

Statistical behavior of carbon monoxide from vehicular exhausts in urban environments

Abstract Air pollutant concentrations are essentially random variables and can be well described by statistical distribution models. The statistical distribution models are, therefore, useful tools in predicting the distribution of air pollutant concentrations. The statistical distributional form, fitting to the concentrations data, is based upon several factors, i.e. source types, pollutant types, emission patterns, meteorological conditions, and averaging times [Taylor, J.A., Jakeman, A.J., Simpson, R.W., 1986. Modeling distributions of air pollutant concentrations – I: identification of statistical models. Atmospheric Environment 20 (9), 1781–1789]. The statistical characteristics of dispersion of air pollutants in the atmosphere are represented by successive random dilution process [Ott, W.R., 1995. Environmental Statistics and Data Analysis. Lewis publishers]. This process may, however, differ depending upon the location of pollutant dispersion, i.e. near roadways, at intersections or in street canyons. Further, the distributional form may also differ. Several investigators, in the past, presumed lognormal distribution (LND) for the air quality data. While, a few found other distributional form when carried out the actual data analysis. The present paper develops the statistical distribution model fitting to carbon monoxide (CO) concentrations for the heterogeneous traffic pattern at the urban hotspots in Delhi, India. Three years of 1-h average CO concentration data (from 1997 to 1999), at the traffic intersection and near a roadway, are examined using goodness-of-fit tests for the suitable statistical distributional form. The results showed that the log logistic distribution model (LLD) best fit the CO concentration data at both the intersection and the roadway. It can therefore be deduced that ‘heterogeneity in traffic’ and ‘emission patterns’ may be affecting the statistical distributional form significantly.

Passive control potentials of trees and on-street parked cars in reduction of air pollution exposure in urban street canyons.

This study investigates the passive-control-potentials of trees and on-street parked cars on pedestrian exposure to air pollutants in a street canyon using three-dimensional CFD. Since, according to some studies trees deteriorate air quality and cars parked roadside improve it, the combine as well as separate effects of trees and on-street parked cars have been examined. For this, different tree canopy layouts and parking configurations have been developed and pedestrian exposure for each has been analysed. The results showed, for example, tree crown with high porosity and low-stand density in combination with parallel or perpendicular car parking reduced the pedestrian exposure considerably.

The impact of traffic-flow patterns on air quality in urban street canyons.

We investigated the effect of different urban traffic-flow patterns on pollutant dispersion in different winds in a real asymmetric street canyon. Free-flow traffic causes more turbulence in the canyon facilitating more dispersion and a reduction in pedestrian level concentration. The comparison of with and without a vehicle-induced-turbulence revealed that when winds were perpendicular, the free-flow traffic reduced the concentration by 73% on the windward side with a minor increase of 17% on the leeward side, whereas for parallel winds, it reduced the concentration by 51% and 29%. The congested-flow traffic increased the concentrations on the leeward side by 47% when winds were perpendicular posing a higher risk to health, whereas reduced it by 17-42% for parallel winds. The urban air quality and public health can, therefore, be improved by improving the traffic-flow patterns in street canyons as vehicle-induced turbulence has been shown to contribute significantly to dispersion.

A method to estimate spatiotemporal air quality in an urban traffic corridor.

Air quality exposure assessment using personal exposure sampling or direct measurement of spatiotemporal air pollutant concentrations has difficulty and limitations. Most statistical methods used for estimating spatiotemporal air quality do not account for the source characteristics (e.g. emissions). In this study, a prediction method, based on the lognormal probability distribution of hourly-average-spatial concentrations of carbon monoxide (CO) obtained by a CALINE4 model, has been developed and validated in an urban traffic corridor. The data on CO concentrations were collected at three locations and traffic and meteorology within the urban traffic corridor.(1) The method has been developed with the data of one location and validated at other two locations. The method estimated the CO concentrations reasonably well (correlation coefficient, r≥0.96). Later, the method has been applied to estimate the probability of occurrence [P(C≥Cstd] of the spatial CO concentrations in the corridor. The results have been promising and, therefore, may be useful to quantifying spatiotemporal air quality within an urban area.

Treatment of gaseous volatile organic compounds using a rotating biological filter

Rotating biological filter (RBF), which provides higher oxygen mass transfer has been developed for treating gaseous volatile organic compounds (VOCs) such as BTEX (Benzene, toluene, ethylbenzene and xylene) at higher concentrations. The screening of enriched cultures has been done initially to enhance the performance of RBF for treating xylene, toluene and xylene, and BTEX at various loading rates. The removal efficiency of BTEX was maximum (82%), higher than toluene and xylene (79%), and xylene (72%). The presence of xylene enhanced the removal of toluene in the mixture. In the BTEX, toluene was found to be highly biodegradable followed by ethylbenzene, benzene and xylene. The RBF also removed nutrients from wastewater along with VOCs. The stability study of RBF showed that supply of nutrient media influenced the RBF performance more. Further, the predominant strain identified in the mixed culture was Enterobacter cloacae SP4001, responsible for biodegradation of BTEX.

Effects of moving-vehicle wakes on pollutant dispersion inside a highway road tunnel

This study investigates the pollutant dispersion in a highway road tunnel in the presence of moving-vehicle wakes by a relative-velocity approach using 3-D CFD (3-Dimensional Computational Fluid Dynamics). The turbulent behavior of airflow around different-shaped vehicles and its impact on the pollutant dispersion have been studied. The different-shaped vehicle geometries were extracted, and simplified and dimensioned basing the typical vehicles on Indian roads. The model has been verified with the literature data of static pressure around a moving vehicle body before applying to simulate concentrations, and validated with on-site data at two locations. The results showed that wakes varied with the size, shape and speed of vehicles. The mixed-traffic flow produced higher near-field wakes and accelerated the piston effect, pushing pollutants toward the tunnel roof and out of exit portal in short-time. The findings have particular significance in the studies related to dispersion inside the tunnels having a mixed traffic of different dimensions and shape.

An open-terrain line source model coupled with street-canyon effects to forecast carbon monoxide at traffic roundabout

A double-lane four-arm roundabout, where traffic movement is continuous in opposite directions and at different speeds, produces a zone responsible for recirculation of emissions within a road section creating canyon-type effect. In this zone, an effect of thermally induced turbulence together with vehicle wake dominates over wind driven turbulence causing pollutant emission to flow within, resulting into more or less equal amount of pollutants upwind and downwind particularly during low winds. Beyond this region, however, the effect of winds becomes stronger, causing downwind movement of pollutants. Pollutant dispersion caused by such phenomenon cannot be described accurately by open-terrain line source model alone. This is demonstrated by estimating one-minute average carbon monoxide concentration by coupling an open-terrain line source model with a street canyon model which captures the combine effect to describe the dispersion at non-signalized roundabout. The results of the modeling matched well with the measurements compared with the line source model alone and the prediction error reduced by about 50%. The study further demonstrated this with traffic emissions calculated by field and semi-empirical methods.

Uncertainty in modelling PM10 and PM2.5 at a non-signalized traffic roundabout

Abstract Uncertainty in inputs to most air quality models of causal nature often results uncertainty in modelled concentrations as well. If incorporated, it may provide complete information on assured range of air pollutant levels. The study presents a sensitivity analysis of models and the probabilistic based estimates of uncertainties in their predictions. Two vehicular exhausts dispersion models have been used for forecasting hourly average PM10 and PM2.5 concentrations at a non–signalized roundabout traffic intersection. The uncertainties were estimated using first–and second–order Taylor series and Monte Carlo methods due to wind speed and wind direction and evaluated with one week particulate matter measurements (PM10 and PM2.5) during winter period. The amount of uncertainty due to wind speed was about 55% in the both models, resulted from wind direction was up to 5 to 20% of the modelled mean for receptors closer to the source but increased even up to 200% as the distance from the source increased. The uncertainty due to wind speed by second–order Taylor series matched with that by Monte Carlo method implying that a simple second–order Taylor series can be utilized for such studies instead of conventional time–taking Monte Carlo method.

Effects of Engineered Nanomaterials Released into the Atmosphere

AbstractEngineered nanomaterials (ENMs) are manufactured for use in nanoproducts and during the lifecycle are released as waste nanoparticles (size <100  nm). The ENMs pose risks to workers and consumers, and when they become airborne, they cause broader effects on the environment and human health. Its increasing proportion in the atmosphere is a potential threat. In this, the past studies are reviewed to identify the types, effect-initiating properties, potential exposure pathways, and determine the effects on humans and atmospheric environment. The ENMs could be more hazardous than silica and asbestos because they are manufactured with specific properties and synthetically developed for wide applications. ENMs such as metals, metal oxides, and quantum dots are biopersistent, whereas fullerenes and single-walled carbon nanotubes cause adverse effects but have a shorter life span. The airborne ENMs may have modified properties and toxicological effects. Therefore, the knowledge of the inhalation toxicity ...