I have two air quality monitoring stations located next to each other next to a busy road. I do not have direct measurements of the urban background concentration. Is there a way to calculate the urban background concentration directly from the time series measurements?
If you have traffic data and meteorological data together with your pollution data, you can build and run a dispersion analysis. The difference between pollution from the sources in your model and your pollution measurement is your background.
That's a good suggestion. Unfortunately, I do not have temporally resolved traffic counts, so this path is not an option.
If your measurement is a time average, you don't necessarily need the time variation of traffic. It would be nice to model the correlation of traffic emission and wind, but averages will still give a reasonably accurate result.
Assuming we are talking about NO2, NOX or PM, you can use the DEFRA National Maps: https://uk-air.defra.gov.uk/data/laqm-background-home.
The LAQM TG16 guidance can be helpful if you want to know more about source apportionment.
if you are looking for background concentrations, you can also have a look at copernicus results...,
at:
http://macc-raq-op.meteo.fr/index.php?category=ensemble&subensemble=hourly_ensemble&date=LAST&calculation-model=ENSEMBLE&species=o3&level=SFC&offset=000
you can get background concentrations (under REANALYSIS link, both hourly and yearly/seasonal averages)
hope it helps
Enrico
When there is no traffic, such as very early weekend morning, the measured concentrations should asymptotically approach the background:
measured concentration =
background concentration
+ constant A * exp (- constant B * time)
If your analyzer has a sufficient time resolution, you will see the concentration increase abruptly after a passage of a vehicle (by a different amount depending on vehicle emissions and dispersion) and then gradually decline.
There is no analytical solution, you have to solve this iteratively.
Michal Vojtisek-Lom
This approach assumes that the background concentration is a constant value. As a significant part of urban background comes from other traffic-related sources, the measured concentration on a weekend morning won't be representative for the rest of the week.
Michal Vojtisek-Lom: Thank you for the suggestion. The time resolution of the sensors is 1 minute, so it is not high enough to resolve individual cars.
The answer to this question is highly depending on which pollutant you are referring. We conducted a 5 year long near roadway monitoring program.For UFP, We found that different wind direction represents different ambient emissions sources and result in different background concentration. However, when coming to CO2, the pollutant concentration is independent to wind directions. Please see:
Concentration of Ultrafine Particles near Roadways in An Urban Area in Chicago, Illinois (2018). DOI: 10.4209/aaqr.2017.09.0347@Thor-Bjørn Ottosen
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