I found a positive correlation between RH and PM2.5 in winter 2013 over Bhubaneswar (21◦15’ N and 85◦15’ E, altitude 45m above sea level), India. Why?
Possibly that they both are high during stagnant weather as the common factor
Dear Dr. Harry, I couldn't able to follow you. How do you justify role of stagnant weather? Please clarify me. During my observations RH was 55-75%.
Thank you.
Dear Dr. Thompson,
We measure PM2.5 by gravimetric method using Low volume Sampler of Polltech India Ltd.
Thank you
In stagnant weather the transport of pollution is slow thus local pollution can accumulate. This also applies to the humidity.
However when your humidity only varies between 55 and 75 % this range is far too small for a significant correlation?
I thought it was say between 30 and close to 100%. Especially this high humidity means that there is almost no wind. In the Ganga Valley that is often the reason for a correlation of fog and high PM.
Thank you very much Dr. Brink. I have gone through some literature suggesting the stagnant weather conditions, but couldn't found them applicable to meteorological conditions of my region. Can you please suggest me other possibilities of positive relation between RH and PM2.5?
I am puzzled that you find a correlation because there is hardly a variation in RH: only a factor of 1.4. I presume that the variation in PM2.5 is much larger than this value of 1.4.
The correlation was not good. Correlation coefficient was only 0.48 and PM2.5 variation was from 36 to 77microgram/m3. Thank you Dr. Brink.
Hi Sipra
I wonder that are you only analyse PM2.5 with gravimetric method? As far as I'm concern, filter weights are known to change in response to relative humidity.
What type of filter do you use to analyze the concentration of PM2.5?
Dear Eliani, I agree that weight of filter papers vary w.r.t. RH, but to avoid these discrepancies we use desiccator before and after weighing the paper.
We use Whattman QM-A filter (Quartz Microfiber).
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