3.6. Indoor/outdoor contribution to carbonaceous aerosols in cultural/ritual-indoors
The average indoor/outdoor ratios are summarized in Table S6, which is usually used to describe the difference between indoor concentrations and the corresponding outdoor levels or as an indicator for the strength of indoor sources [24,49e51]. In other words, the Indoor/outdoor ratio is an indicator of whether indoor levels are influenced by significant indoor sources of air pollutants or if indoor levels are the result of outdoor concentrations. Indoor
air pollutants concentrations are affected by infiltration of outdoor pollutants into the homes and indoor sources [9,24]. The ratios of I/O at different sites reveal the importance of outdoor versus indoor, better than absolute concentrations. The average mean I/O ratio was greater than unity for both particulate fractions at all indoor sites (1.33e8.38 and 1.39 to 10.09 for PM10 and PM2.5 respectively), reveal that outdoor penetration was minimal in indoor sites. Highest I/O ratio was found in MHS-indoors and lowest in residential-indoors for both fractions. PM2.5 fraction shows higher I/O ratios than PM10 fraction at all indoor sites, which imply much stronger presence of PM2.5 than PM10 from indoors. These results are consistent with previously reported study in northcentral India [9]. Thatcher et al. [8]revealed that coarse particles have larger deposition velocities than fine particles which lead to
reduction in their indoor concentrations, as they fall out by gravitational settling or deposit on window and doors frames.