According to Popular Mechanics (https://www.popularmechanics.com/science/energy/news/a27112/pollution-can-block-25-percent-of-solar-power/#:~:text=They%20found%20that%20solar%20panels,of%2035%20percent%20or%20more.): “They found that solar panels in very dirty environments saw a 25 percent drop in efficiency from atmospheric pollution alone. Combining these two effects, a solar panel located in a heavily polluted environment that hasn't been cleaned in a month or more might see a total efficiency drop of 35 percent or more.” With that said, we would recommend regular maintenance cleaning to keep up the efficiency of your solar investment.