Might that have something to do with the fact that farms account for more land area than cities? And the fact that they didn't count some particulates commonly produced in cities?

Edit; oh, and this was a computer simulation, just so you guys know.

Are all <2.5 micrometer particles equally damaging, or does the chemical constitution of the particle affect the harm it does?

Even more reason to pave over farm land, and build more housing estates!

We get to have even more people move here, and we actually reduce pollution!

It's win win.

Excerpt from the linked summary^1 about research published in City and Environment Interactions:^2

>First author Dr Jamie Kelly, who conducted the research while based at UCL Geography before moving to the Centre for Research on Energy and Clean Air, said: “We were surprised to find how pervasive the contribution of agricultural emissions of ammonia to particulate pollution really is.

>“Particulate pollution across the UK is dominated by aerosols formed from rural agricultural emissions of ammonia. This influence extended from rural areas to mid-sized cities like Leicester, large cities like Birmingham and, for the UK, anomalously large cities like London.

>“This is because ammonia and aerosol particles can stay suspended in the atmosphere for days to a few weeks and so be transported long distances.”

>This kind of fine particulate pollution can have serious health effects, with estimates saying it may contribute to between 29,000 and 99,000 additional premature deaths each year in the UK.

>&nbsp;

>The team ran multiple simulations with different pollution sources turned on and off, to see how each source contributed to the spread of particulate pollution.

>They found that UK agriculture contributed 38% of the particulate pollution in Leicester and 32% in Birmingham. Even in large cities like London, agriculture contributed 25% of the city’s pollution.

>Cities only contributed between about 13-24% to their own pollution, mostly from traffic, energy production, industry, and furnaces in commercial and residential locations.

>Senior author Dr Eloise Marais (UCL Geography) said: “Our work has identified that addressing urban air pollution doesn’t only require local solutions like ultra-low emission or clean air zones, but also national-scale measures that reduce ammonia emissions from rural agriculture.

>“Such actions have potentially large health benefits, as the fine particulate matter pollution formed from ammonia is a leading global health risk.”

^1 University College London, 31 Mar. 2023, https://www.ucl.ac.uk/news/2023/mar/farms-found-be-biggest-particulate-pollution-source-citie

^2 Jamie M. Kelly et al. Diagnosing domestic and transboundary sources of fine particulate matter (PM2.5) in UK cities using GEOS-Chem. City and Environment Interactions 18, 100100 (2023). https://doi.org/10.1016/j.cacint.2023.100100

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