Measurements of optical properties of black and brown carbon using multi-wavelength absorption technique at Mumbai, India

The multi-wavelength absorption along with particulate matter (PM2.5) measurements of ambient aerosols was carried out at an urban city of Mumbai, India. The wavelength dependence of the light absorption depicted by black and brown carbon is utilised to determine their absorption angstrom exponent (AAE). Absorption coefficients of black carbon (BC) and brown carbon (BrC) were found using an extrapolation technique. The AAE for BC at the sampling location was found to be 1.1 +/- 0.05 and that for BrC was found to be 4.4 +/- 2.1. The BrC absorption coefficient (sigma(BrC)) at 370 nm averaged over the month for the sampling period (September 2017-May 2018) ranged from 2 to 28 M m(-1) and BC levels ranged from 1.5 to 22 mu g m(-3) with the mean of 7.6 +/- 5 mu g m(-3) for the sampling period. The diurnal variation of BC, sigma(BrC)(370 nm), AAE(BC) and AAE(BrC) were explored across different seasons. The BC and sigma(BrC)(370 nm) exhibited two-peak diurnal variation with the highest peak recorded in the winter season. With respect to diurnal changes, AAE(BrC) showed considerably larger variation in comparison to AAE(BC). At the sampling site, BrC contributed 6.8 +/- 3% to a total aerosol light absorption at 370 nm and major absorption came from BC.

Automated summary

The multi-wavelength absorption of ambient aerosols in Mumbai, India was measured, and the wavelength dependence of light absorption was analyzed. The absorption coefficients and angstrom exponents of black and brown carbon were determined. Brown carbon showed higher absorption coefficients and angstrom exponents compared to black carbon, with significant seasonal variations. Brown carbon contributed less to the total aerosol light absorption at 370 nm.