id summary reporter owner description type status priority milestone component version resolution keywords cc 329 Bias of footprint dependant on particle number cluekenwinkels "Hello, I currently use `FLEXPART-WRF` in an urban setting on roughly 1 km resolution. In a test for the statistical error due to the limited particle number, I found not only statistical, but systematic differences (bias) between runs with different particle numbers. In particular, the sum of the footprints entries grows with the particle number. As I understand it the footprints' values should not generally grow with larger partical numbers, but become more and more consistent, which is not the case here. The same footprint was calculated for 10, 50, 250, and 500 thousand particles with very different results for the same release location, time and meteorology. The lowest paritcle number is chosen due to the vaule in reviewed papers using `FLEXPART-WRF` in an urban/meso scale setting: - Cui 2015 https://doi.org/10.1002/2014JD023002 (10,000 particles per release) - Nathan 2021 https://doi.org/10.5194/acp-2020-1303 (10,000 particles per release)." Defect closed critical FP other FLEXPART-WRF fixed