What these and other rainfall pH data show is that the average pH of rainfall events in Big Sur over the past four years fluctuates significantly, with values spanning an entire unit of pH. This means that some events are 10 times more acidic than other events. Who knew that the rainfall pH of individual weather systems varies to such a degree?
Could these fluctuations be due to sampling error? Almost certainly not. After each set of measurements I check the accuracy of the pH meter and sensor using the 4.00 and 7.00 standards used in the calibration. For the 29 sets of samples measured so far this rainy season, the 4.00 and 7.00 standards were measured at 3.99 ± 0.02 and 6.99 ± 0.01, respectively. That darn good accuracy in my opinion.