What’s the difference between particulate and particle?
Should it be diesel particulates or diesel particles, and why?
Could you provide three or more examples where it should use particulate rather than particle?
The US Clean Air Act designates six criteria pollutants, for which national ambient air quality standards (NAAQS) have been set: Nitrogen Oxides, Sulfur Dioxide, Lead, Ozone, Carbon Monoxide, and Particulate matter. The EPA and state regulatory agencies throughout the US (and other developed countries) regulate emissions of air pollutants, with special attention paid to the criteria pollutants.
When the topic is air pollution, and especially the regulation of air pollution, the only of the two terms used is particulate. You might use any of the following collocations:
The plural form of particulate matter, (i.e., different types of particulate matter) is particulates. So the term diesel particulates will usually be understood to mean "particulate matter emitted from diesel combustion falling into various size ranges (typically <2.5 microns, and <10 microns, which are regulated categories)."
The phrase diesel particles would mean "a mist of uncombusted diesel fuel".
For further clarity on the usage of particulate, I'll incorporate the full OED entry for the term which contains a large number of examples of its use:
Particulates are things made up of particles. Diesel particulates are made up of particles of various exhaust gases, for instance.
The phrase you are looking for here is diesel particulates, because that is the normal word used when you are talking about the by-products of combustion and a pollutant. The other does not make sense for this case.
You can have dust particles and subatomic particles, but the stuff that pollutes the air is always fine or coarse particulates.
I don't really like to post this, because I've already agreed with and upvoted tchrist's answer, but...
...which I think suggests the smart money should be on diesel particles. Note that there's not much point in graphing earlier usage - hardly anyone knew/cared/wrote about contaminants in diesel exhaust until the late 70s.
It was used adjectivally (in scientific contexts) a century before OED's first citation of particulate as a noun in 1960. That was the UK-based New Scientist, referring to nucleoproteins, coenzymes and cell particulates. Next they've got Nature (UK/US/global) in 1971 writing of airborne particulate (note the singular form). A few years later it was the word initially dominating usage in relation to diesel particulate (again, primarily as a singular noun, meaning "stuff composed of particles").
I can't explain why particulates started being used for the particles themselves. Perhaps someone thought it was "prestigious/academic". But if that graph trend means anything, I doubt the usage will endure.
EDIT: In light of a few downvotes, I've amended my chart to include the singular form, which has clearly always been more common. I have no problem with that one - it's a natural extension from the long-established adjectival usage to refer to [some] particulate matter as a particulate.
The problem is when people pluralise the term (which is what OP asks about). We don't normally speak of smokes around industrialised urban areas, or say ices are produced when water freezes. When people use the term diesel particulates, they're not normally thinking in terms of many "interdispersed" particulates from many separate instances of combustion - what they have in mind is the billions of tiny particles in the air produced from those sources.
It's true that strictly speaking, diesel particles should mean tiny globules of (unburnt) diesel vapour. Quite possibly some people even think that's what the particulate consists of, I don't know. The point is usages such as small particulates are inherently "strange", since they lead people (including OP) to think particulates are some special kind of small objects suspended in gas/liquid.
Although particulate is currently often as "shorthand" for a particle within a particulate in scietific/industrial contexts, it's actually quite rare to see a single particle referred to as, for example, a large particulate (most examples in that link quite clearly mean particulates made up of (relatively) large particles).
I remain of the belief that technical usage will mainly stick with singular usage as a "mass noun", and popular usage will increasingly adopt diesel particles when they mean "bad stuff in the air caused by diesel combustion". This seems both logical, and consistent with the trends in my graph.