3.5. Relationship between OC and EC to address specific cultural/
ritual burning source indicators
The relationship between OC and EC gives some indication of the origins of carbonaceous aerosols [50]. Therefore, OC to EC ratios were used to study the emission and transformation characteristics of carbonaceous aerosols [49]. Values of OC/EC ratio greater than two suggest the formation of secondary organic aerosols apart from primary emission sources. Therefore, the OC/EC has been used to indicate the presence of primary and secondary organic aerosols [50]. The OC/EC ratios for cultural/ritual-indoors along with residential indoors and ambient-outdoors in PM2.5 and PM10 are given in Table S3. As shown in Table S3, the ratios of OC/EC ranged from 2.50 to 6.85 and 2.38 to 6.42 in PM10 and PM2.5 respectively for cultural/ritual-indoors alongwith residential indoor. The highest
OC/EC ratio was observed at MHS-indoors (6.85 and 6.42 in PM10 and PM2.5 respectively), higher than earlier reported values for different indoor sites [49]. This may be caused by the strong OC related sources such as combustion of Styrax benzoin and incense sticks. The high OC/EC ratio can be attributed to the presence of emissions of carbonaceous aerosols from source with a high OC/EC ratio [49]. Lowest OC/EC ratio was found in HT-indoor with values 2.38 and 2.50 in PM2.5 and PM10 respectively. This might be due to the higher number of flaming episodes compared to smoldering ones. The origin of carbonaceous particles can be estimated on the
basis of the relationship between OC and EC. To assess the origin of carbonaceous particles measured in indoor environments, the regression statistics between OC and EC concentrations has been shown in Table S5. Correlation between the EC and OC measurements imply the similarity of emission sources between OC and EC. It is considered that the weaker the OC-EC correlations, greater difference between OC and EC sources in the indoor environments
[6]. OC-EC correlations at all cultural/ritual sites are strong (R2 > 0.9). It implies that a majority of the indoor OC comes from emission source similar to those responsible of EC (eg. material used for worshipping events). Meanwhile, the OC-EC correlation is moderate at residential-indoors (R20.55). Thus it indicates that part of the OC in the residential-indoors is coming from indoor source (cooking), while remaining OC and EC coming from outdoor
sources. In contrast, the OC-EC correlation was weaker for AMBOUT attributed that different sources are responsible for the origin of OC and EC at AMB-OUT.