Carbonaceous aerosols in restaurants: optical properties and possible impact on climate

Organic carbon is a significant constituent of PM_2.5. The organic carbon percentage in indoor microenvironments is higher than in the ambient environment. Water soluble organic carbon (WSOC) is responsible for altering hygroscopicity, hence determining the ability of particles to act as cloud condensation nuclei (CCN). In this study, quartz fiber filters were collected from two restaurants (R1 and R2 ) using an Airmetrix low-volume sampler at a 5 lpm flow rate. R1 was a closed restaurant where dining tables and the cooking locations were adjacent to each other. R2 was a semi-indoor environment; two sides of the dining place were open with adjoining dining tables, and cooking locations. Organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) were estimated using DRI thermal optical analyzer and total organic carbon analyzer instruments. All these constituents can exfiltrate outdoors and alter the climate. Absorption coefficient (b_abs)  and Mass Absorption Efficiency (MAE) were calculated for Water-soluble carbon at 365 nm. Average OC and EC concentrations were very high in R1, i.e. 160.31 µg/m³ and 14.99 µg/m^3,respectively. It was lower in R2, i.e., 29.61 µg/m³ and 4.88 µg/m^3,respectively. As there was a direct biomass burning source, i.e., cooking, the major portion of the OC was POC. In R1, the average POC was ~67%, and in R2, ~60% of the total OC. The average WSOC percentages in the R1 and R2 were 8.01% and 25.21%, respectively. MAE values were comparable, i.e., 0.04 and 0.03 in R1 and R2, as the nature of the source was similar. Brown Carbon (BrC) absorption peaks at 365 nm were observed in both locations, confirming its presence. A negative correlation was observed between b_abs and WSOC, indicating BrC as the main absorption component of the WSOC. The effective carbon ratio (ECR= SOC/[POC+EC]) was calculated to estimate the impact of the particles on the local radiative energy balance. The values were 0.42 in R1 and 0.51 in R2. Aerosol generated from both locations was more absorbing in nature than scattering. In the R1, the aerosol had more absorption capability than in R2 . This study did not quantify the amount of  WSOC and BrC from different food and cooking fuels. But, from this study, it was noticed that cooking-related aerosols are absorbing in nature and can exfiltrate outdoors and alter the local climate.

Keywords: Water Soluble Organic Carbon, Mass Absorption Effiency , Effective Carbon Ratio, Brown Carbon