Continuous data of aerosol optical thickness monitored using differential optical absorption spectroscopy (DOAS) are correlated with the concentration of ground-measured suspended particulate matter (SPM).A high correlation is found between the DOAS and the ground SPM data, making it possible to calculate the mass extinction efficiency of the aerosols in the atmosphere. It is found that the value of mean mass extinction efficiency (MEE) varies over a range of 2.6-13.7 m2 g-1, with smaller and larger values occurring for size distributions dominated by coarse and fine particles, respectively.