Diurnal, weekly, seasonal, and interannual variations of urban aerosols were analyzed with an emphasis on summer months using 4-years of the National Aeronautics and Space Administration (NASA) Earth Observing System (EOS) Moderate Resolution Imaging Spectroradiometer (MODIS) observations, in situ AErosol RObotic NETwork (AERONET) observations, and in situ EPA PM2.5 data for one mid-latitude city (New York) and one sub-tropical city (Houston). Seasonality is evident in aerosol optical thickness measurements, with a minimum in January and a maximum in April to July. The diurnal variations of aerosols, however, are detectable but largely affected by local and regional weather conditions, such as surface and upper-level winds. On calm clear days, aerosols peak during the two rush hours in the morning and evening. Furthermore, the anthropogenic-induced weekly cycles of aerosols and clouds are analyzed, which by themselves are weak as the anthropogenic signal is mixed with noise of natural weather variability. In addition, corresponding cloud properties observed from MODIS demonstrate an opposite phase to the seasonality of aerosols. Nevertheless, no clear relationship was observed between monthly mean aerosols and rainfall measurements from NASAÕs Tropical Rainfall Measuring Mission (TRMM), implying that in the summer the aerosol impact may not be the primary reason for the change of urban rainfall amount.