The dataset's assignee ranking is concentrated at the top, with a long tail of single- or few-filing entrants behind it — a pattern typical of a field with both large industrial equipment makers and many auto-parts and engine OEMs filing narrower, application-specific claims. Rather than a single dominant holder, activity splits between stationary flue gas equipment specialists and mobile-source emission-control filers, since the search spans both B01D scrubber technology and F01N/F02D engine exhaust treatment. Checking the ranking table directly, rather than relying on any single figure, is the reliable way to see this split.

Filings declined from a peak of 185 in 2017 to 5 in the most recent partial year, with a midpoint of 50 in 2022 — a clear downward trend, not a plateau. Some of that recent-year drop is an artefact of publication lag, since patent applications typically publish around 18 months after filing, so the last one to two years understate true activity. Even accounting for that lag, the multi-year decline from the 2017 peak indicates the core claim space in scrubber and SCR chemistry is largely occupied rather than expanding.

In this dataset, flue gas desulfurization work sits mainly under B01D (separation processes, 2,357 records) and F23J (flues and combustion residue, 203 records), covering wet and dry scrubbing, sorbent chemistry and byproduct handling from stationary sources like power boilers. Selective catalytic reduction and related exhaust treatment sits under F01N (1,727 records) and F02D (engine control, 335 records), and is concentrated on mobile-source and engine-integrated systems. The two routes overlap in catalysis (B01J, 382 records) but otherwise target different plant architectures, which shows up clearly in the split between stationary-equipment assignees and automotive OEMs in the ranking.

That Ford Global Technologies filing claims an exhaust system architecture combining a reductant injection point with an integrated particulate-filter-and-SCR unit arranged in series within a single exhaust passage. It blocks systems that follow that specific integration and ordering, not SCR or particulate filtration used independently or in separate housings. Anyone designing a combined aftertreatment unit should check the ordering and physical integration of their own design against this claim rather than assuming an SCR or filter component alone infringes.

The thinnest documented classes are C01F (alkaline-earth, aluminium and rare-earth compounds, 94 records) and F02B (internal-combustion engine design, 106 records), both well below the 2,357-record density of the core separation-process class. Co-assignee collaboration is also sparse, with only 10 pairs recorded in total and each pairing confined to a single industry segment, suggesting cross-sector work on byproduct valorisation or combined SOx/NOx sorbent regeneration is underdeveloped. These smaller classes, and the intersections between them and the dominant scrubber/SCR art, are where a narrower, less-contested claim is more likely to be available.