| Summary: | The total contribution of the small (radius ≤ 0.35 µm) and medium (radius ≤ 0.7 µm) sized particles as a defined by MISR (Multi-Angle Imaging SpectroRadiometer) to the Aerosol Optical Depth (AOD) is correlated to the AERONET (Aerosol Robotic Network) fine mode fraction of AOD. According to this thesis the contribution of particles having radius ≤ 0.7 µm to the measured AOD can either increase or decrease with increasing relative humidity, depending on the initial function of aerosols. Instinctively it appears that since the aerosols swell up according to their hygroscopic properties with an increase in relative humidity, the contribution of particles having radius ≤ 0.7 µm to the AOD (defined here as fine mode fraction of AOD) should decrease. Although this is true for certain size distributions, it is not true for all size distributions. However, often the increase in fine mode fraction of AOD as derived from AERONET / Satellite based instruments are interpreted as an increase in fine particle pollutants of anthropogenic origin and a decrease in fine mode fraction is attributed to enhanced dust activity or influence of larger marine aerosols without considering the influence of relative
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