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What causes the “missing mass” in PM2.5 measurements?

We're using standard gravimetric filters and following protocol, but there's consistently a gap around 30% between what we measure and what models predict should be there based on source apportionment. This error margin is too large to ignore for our health impact studies. I need to understand what material species or artifacts we are likely failing to capture with our current method.

 

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By Prajwal Sharma Answered 2 years ago

From my experience running monitoring networks, this "mass closure" problem is very common. The primary culprit is usually semi-volatile material that evaporates from your filter after collection, either during handling or due to temperature changes. This includes certain organic compounds and ammonium nitrate. I have also seen significant contributions from particle-bound water, which standard gravimetry misses. I would recommend complementing your filter method with an online instrument like an Aerosol Chemical Speciation Monitor (ACSM) to capture the dynamic, volatile fraction in real-time and close that budget.

 

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