It should be determined by some metal markers (meaning originating from traffic etc.) but I cannot find any source which would describe it. Thanks.
Answer
The main idea is the following: you will need multiple sampling points and record enough data to obtain a representative dataset. Then when drawing wind roses with high percentiles (let say P95 or above) you will be able to easily point out an unique source of a relevant and exclusive pollutant.
But of course, reality is much complex... And there are some adverse effects that you must address before pointing out the source with a reasonable confidence.
First you better be not so close to the source, in order to measure immission instead of emission. Then environment and local conditions will average out. And wind speed, wind direction and concentrations become meaningful. In this case high percentiles likely originate from your source.
Second, your analyte must be relevant and if possible exclusive from your source. Measuring CO2 is not a good choice when monitoring traffic (it is stable, widespread thus global and not exclusively produced by traffic), NO is a better one because it is local, reactive and strongly related to high compression ratio thermal engine combustion source.
Third, if there are multiple isotropic sources, you will get nothing useful using wind roses. And your problem becomes really tricky.
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