Can reduced NOx emissions lead to increased PM2.5?
Anil Gogebakan
I have a question regarding the potential relationship between reductions in NOx emissions and PM2.5 concentrations. While it might seem counterintuitive, I’m not a chemist and am uncertain about how chemical reactions in the atmosphere might be influenced by such changes. My preliminary results using InMAP suggest that PM2.5 concentrations have increased, even though NOx and SO₂ emissions from fossil fuel power plants have, on average, declined.
Could it be possible that reductions in NOx and SO₂ emissions might contribute to an increase in PM2.5 concentrations? If so, do you know of any studies or resources that could help explain this phenomenon?
I’d greatly appreciate your insights on this. Thank you in advance for your help!
Anil Gogebakan
Thank you for your response! I’ll look into it and try to understand how it works. In the meantime, could you please provide an example of how the calculation method might result in PM2.5 increases when NOx and/or SO2 levels decrease?
I also have a quick follow-up question: I’m simultaneously inputting positive and negative changes (average change is a decrease for both pollutants) in NOx and SO2 emissions into InMAP. Could this approach be responsible for the PM2.5 increases that InMAP calculates? What are your thoughts on this?
Hi Anil-There can be cases where modeling shows an increase in PM2.5 via secondary organic aerosols with decreases in NOx emissions. There are some articles about this in Southern California where there could be transitions between NOx-limited and VOC-limited regimes.However, I think you can also see increases in PM2.5 between InMAP runs with decreases in emissions depending on how you are computing the differences between scenarios and artifacts due to the variable output grid sizes.-Dave
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Anil Gogebakan
If you have outputs with different spatial resolution (due to the InMAP dynamic grid) and do simple spatial difference operations, I think you could get local increases in PM that are artifacts of the spatial math. For example, if you have a point source of PM2.5 and InMAP creates a 1km grid around the source, the grid cells upwind will have much lower concentrations than downwind. If you run a second scenario with lower emissions and InMAP creates 4km cells in that area, a point upwind may be included in the same cell as the source and have a higher concentration compared to the first case.
The locations of the increases and decreases in emissions are critical to the resultant PM2.5 concentrations, so it's entirely possible to have aggregate decreases in emissions and increases in PM2.5 concentrations due to variations in local conditions. That's the work that InMAP does. And of course, exposure is dependent on the distribution of population.
-Dave
From: Anil Gogebakan <gogeba...@gmail.com>
Sent: Friday, December 13, 2024 8:54 AM
To: David Reichmuth <DReic...@ucsusa.org>
Cc: inmap-users <inmap...@googlegroups.com>
Subject: Re: Can reduced NOx emissions lead to increased PM2.5?