INDOOR AIR QUALITY ASSESSMENT AND SOURCE APPORTIONMENT OF AIRBORNE PARTICLES

Abstract

Indoor Air Quality (IAQ) has become a global concern as people spend around 80 to 90 percent of their time in different indoor environments, such as offices, homes, care centres, schools, universities, shopping centres, etc. The air inside the microenvironments is contaminated with a broad range of pollutants, which are either originated indoors or infiltrated from outdoor. Numerous studies have linked the exposure of infdoor air pollutants with detrimental health effects. Several studies on air quality in schools and workplaces have underlined the effect of poor air quality on comprehensive learning, academic performance, and work productivity. Only a few studies have characterised the IAQ for the universities and higher education institutions – particularly in the Indian context. These educational institutions are the central place for potential learning, research and scientific discoveries, where the young students and scholars spend a significant part of their time. Therefore, the present study attempts to characterise the IAQ of different indoor microenvironments (IMs) of the Indian Institute of Technology Roorkee (IITR), India. This research work aims to quantify IAQ of various indoor microenvironments of IITR followed by physicochemical characterisation of airborne particles and identification of their source contribution. A comprehensive IAQ assessment was carried out for microenvironments of different usages, which include lecture hall complex, central library, offices of the administrative building, and laboratories of IITR. Indoor pollutants (i.e., PM10, PM2.5, PM1 and total volatile organic compound) and comfort parameters (i.e., carbon dioxide (CO2), temperature and relative humidity) were monitored during monsoon, winter and summer seasons from August 2018 to June 2019. The occupants’ perception about IAQ of studied microenvironments was analysed from 137 valid responses. The IAQ was found to vary significantly (Shapiro-Wilk test statistic: P<0.05) among the studied microenvironments. The highest concentrations for indoor PM10, PM2.5 and CO2 were found in lecture halls with concentrations exceeding the guidelines values and comfort limit by ~219%, 333% and 70%, respectively. The higher total volatile organic compound (TVOC) levels with exceeding the threshold limit by ~185% were recorded in the laboratories. The ventilation rate in the studied lecture halls and offices were found below the recommended American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) values. Indoor concentrations of PM10, PM2.5, and TVOC showed strong seasonal variation (Independent sample test statistic: P < 0.05). The mean indoor PM10, PM2.5, and PM1 concentrations during the winter season were found up to 2.1, 3.4 and 4.5 times higher than summer, respectively. During the winter season, the indoor PM10, PM2.5 and PM1 concentrations were found higher in the winter season, ranging from 18.8 μg/m3 to 159.7 μg/m3, from 18.2 μg/m3 to 108 μg/m3, and from 9.8 μg/m3 to 93.8 μg/m3, respectively. The indoor microenvironments having natural ventilation with open windows showed greater seasonal variation than an air-conditioned microenvironment. Indoor to outdoor (I/O) ratios of PM2.5, TVOC and CO2 concentrations were found to be greater than 1. Indoor activities, ventilation and occupancy, were responsible for seasonal and spatial variability among indoor microenvironments. The physicochemical characterisation of indoor airborne particles using Field Emission Scanning Electron Microscopy (FESEM) analysis showed the presence of mineral particles, soot aggregates, and Al-Ca-Fe rich particles of different morphologies. The particles micrographs revealed that the airborne PM were mainly comprised of spherical/semispherical particles, sharp-edged crystal particles, aggregated and chain-like particles. The particles having Feret’s diameter (df) less than 2μm were found in dominance in all the studied FESEM images of different indoor microenvironments. The Energy-Dispersive X-ray (EDX) spectrum obtained from FESEM-EDX analysis had shown peaks of several elements such as iron (Fe), aluminium (Al), carbon (C), oxygen (O), fluorine (F), calcium (Ca), potassium (K), magnesium (Mg), silicon (Si), cadmium (Cd), nickel (Ni), copper (Cu), chlorine (Cl), and zinc (Zn) which revealed the presence of metals in the collected indoor particles at a significant concentration. The quantitative estimation was carried out of the sampled airborne particles for fourteen heavy metals, including Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb and Zn, with Inductively Coupled Plasma Mass Spectrometry (ICPMS). Fe was found at a maximum concentration in particles, ranging from 6.41 ng/m3 to 48.28 ng/m3, followed by Al ranging from 4.03 ng/m3 to 34.58 ng/m3. The Positive Matrix Factorization (PMF) was applied to elemental concentrations of airborne particles collected from several indoor microenvironments to identify potential sources of indoor PM. Four source factors were found optimal for a stable and robust PMF solution. The PMF results indicated that soil/ resuspended dust and fuel oil combustion (~70%), wall dust and furniture (13%), vehicular emissions (~13%), and long-range transport of industrial pollutants (4.5%) were the primary contributing sources to indoor PM during the monitoring period. This study will expand the understanding of IAQ characterisation of microenvironments of the higher education institutes in India as well as worldwide. The present study findings call for executing effective measures for adequate ventilation to decrease indoor contaminants and hence the associated exposure. The outcomes of the source apportionments analysis particularly contribute to identifying major sources of air pollution and therefore facilitates scopes of taking plausible control measures. The study can be a stepping stone for the stakeholders and policymakers to design a management framework for IAQ and to develop standard IAQ guidelines for various indoor settings in India.