Deposition of particulate matter (PM) onto solar photovoltaic (PV) panels - known as soiling - has been estimated to reduce energy production by 10-40% in many regions of the world. Despite this, many key properties including soiling rates, PM source contributions, physical and optical properties of the deposited particles, and the impact of rain and relative humidity (RH) are not well understood. With this in mind we conducted a field study in Gandhinagar, India. Our approach combines soiling monitoring with a reference station and a low-cost digital microscopy system, sample collection for mass loading information, glass sample slides for size resolved soiling impacts, and monitoring of rain, RH, and panel temperature for insight into meteorological impacts on cleaning and soiling rates. Results indicate soiling reduces PV energy production by 0.37 +/- 0.09% day(-1). The low cost (< 100$) digital microscope estimated soiling within similar to 1% of measured losses, confirming the feasibility of this low-cost alternative to expensive soiling stations. Deposited PM decreased energy production by 5.12 +/- 0.55% per PM mass loading (g m(-2)). Microscopy analyses of field samples revealed that > 90% of deposited mass loading is from particles > 5 mu m in diameter, with > 50% of the soiling impacts estimated to be from particles < 5 mu m. While heavy rain cleaned PV panels, light rains and high RH contributed to a 2x soiling rate and 5-10x PM deposition velocities as compared to dry periods.