Spatial heterogeneity of indoor carbonaceous aerosol levels and characteristics: comparison with the outdoors and implications for secondary organic aerosol formation and health effects

Abstract

This research examined the composition of PM_2.5, focusing on elemental carbon (EC), and organic carbon (OC), in six distinct indoor microenvironments (IMEs) and their associated outdoor locations (ODs). Four of the IMEs were located within the academic campus, Indian Institute of Technology Bombay (IITB), while two were situated within 500 m of IITB. Total carbon (TC = OC + EC) constituted 24.49–45.28% of indoor PM_2.5 and 22.87–38.64% of outdoor PM_2.5. Generally, the campus IMEs exhibited lower average PM concentrations compared to outdoor levels, with the dining room (IME4) being an exception. Indoor secondary organic carbon (ISOC) exceeded outdoor secondary organic carbon (OSOC) in all IMEs, apart from the library (IME3). All EC originated from outdoor sources in two campus-based IMEs—the hostel room (IME1) and the laboratory (IME2). IME4 and IME5 had over 30% of EC generated from indoor sources. OC2 and OC3 comprised over 70% of OC in IME4 and IME5. The study used the indoor-to-outdoor ratio of SOC/OC (I/OS_OC/OC) as an indicator for the favorability of chemical transformation inside an indoor microenvironment. The Total Respiratory Deposition Dose (TRDD), calculated using International Commission on Radiological Protection(ICRP) respiratory model, of EC was higher (> 0.030 µg/min) in indoor microenvironments with indoor sources present. The residential microenvironments with tiny volumes showed maximum favourability of the OC transformation to SOC. The study quantified health effects by calculating the number of passively smoked cigarettes (PSC). Number of PSC was > 2 for lung cancer and cardiovascular mortality in most of the studied locations.