There hasn’t been any rigorous study about the accuracy of the SDS011 so far. However, there are evidences that the measurements can represent pretty well the reality.
First, you can see pretty good matching between some sensors and the monitoring stations on a local level, as it is shown on figure 1.6 below.
Second, such matching has also been observed on an international level, as you can see on figure 1.5 below.
Third, the National Dutch Institute for Public Health and the Environment (NDIPHE) has conducted an experiment to test the accuracy of the data collected by the SDS011.They spread 110 DIY sensors in the end of 2017 in December in The Netherlands. After one month of measurements, they compared the data collected with the ones from the 40 official monitoring stations located in the Netherlands. They concluded that the correlation was pretty good after slight calibration of the data (see figure 1.7 below) and hope they can use the sensors for official air pollution monitoring in the future. Watch the video about this test here.
However, the sensors’ measurement get abnormally high when humidity gets high, and too low with dry conditions. You should thus not take consideration of the measurements when it rains nor on very dry days. In those situations the data should be either dropped or calibrated. You should also always compare the measurements with official ones.
Those clues can still let us assume that the data collected is good enough to raise awareness among citizens and give an idea of the pollution of the air. However, it is important to make a serious research about the sensor’s accuracy is the future, to know if the data is usable or not for scientific research such as epidemiology or other.