For the particles, yes, and that is measurable. For the gases, the honest answer is that nobody can tell you, because there is no rating system to tell you with. Wildfire smoke is both.
A portable air cleaner sized properly for the room and run on its highest fan speed reduces airborne particles — that is what the CADR rating measures. It says nothing about the gas fraction of smoke, because in EPA's words there are no widely used performance rating systems for air cleaners designed to remove gases and the CADR system is for particles only. Size on the smoke CADR, run it flat out, and make sure it does not produce ozone.
Clean air delivery rate is measured against three particle sizes — tobacco smoke, dust and pollen — standing in for small, medium and large. The smoke figure represents the smallest particles and is therefore the one to size on.
EPA states it plainly: "there are no widely used performance rating systems for portable air cleaners or filters designed to remove gases. The CADR rating system is for particles only." Wildfire smoke is a mixture of particles and gases. A unit sized perfectly on CADR is addressing one half of it, and there is no equivalent number for the other half. That is not a reason to skip the purifier. It is a reason to distrust anyone who tells you a machine makes smoke go away.
CADR rates one of these two things. Nobody rates the other.
For the gas fraction, EPA's guidance is an activated carbon or other absorbent filter, which can be effective when there is a large amount of material in it — thicker is better. It also notes that research has not yet shown plasma, photocatalytic oxidation or UV light to remove gases effectively in portable residential air cleaners. So the question to ask a seller about smoke is how much carbon is in the filter, and the answer you want is a weight, not an adjective.
EPA's guidance for smoke events is to place the unit where people spend the most time, run it as often as possible on the highest fan speed, and choose one sized for the room it is in.
That highest-speed instruction is doing more work than it looks. EPA states the CADR rating "is typically measured at the air cleaner's highest speed", and separately that a unit filters less air at a lower speed. So the rated number and the smoke-event instruction line up: the figure on the box only describes the machine on the setting EPA is telling you to use.
On sizing, two published rules exist and they agree closely. EPA's own table asks for 65 cfm of CADR at 100 square feet rising to 390 at 600, calculated on an 8-foot ceiling. AHAM's rule of thumb is that the CADR should be at least two-thirds of the room's area. Worked into air changes those come out at about 4.9 and 5.0 per hour, which is also where EPA and CDC's ventilation guidance sits for indoor spaces.
EPA does not publish an air-change target specific to smoke, so we are not going to invent one. What we can say is that the general guidance lands near five air changes an hour, that plenty of coverage claims printed on boxes work out to one, and that the difference is worth knowing before a smoke week rather than during it.
Enter a room and it gives the minimum smoke CADR that EPA’s table and AHAM’s rule each call for. Enter the CADR and the coverage area off a box as well and it converts that claim straight into air changes per hour.
Open the calculatorEPA's approach for a smoke event is to establish a room you can keep cleaner than the rest of the house and put the unit there. That is a sensible use of a device that treats one room, and it is a reminder that a portable air cleaner does not treat a house.
On the central system, EPA advises a filter rated MERV 13, or as high as your system fan and filter slot can accommodate. One caveat comes from EPA's own guide and is easy to miss: furnace and HVAC filters only filter while the system is running, and in most cases residential systems run less than 25 % of the time during heating and cooling seasons. A high-MERV filter in a system that is off is not filtering anything, which is why the fan setting matters during a smoke event.
EPA's wildfire guidance includes a specific instruction: make sure the portable air cleaner does not produce ozone. EPA warns that units containing electrostatic precipitators, ionizers, UV lights without adequate lamp coatings and plasma air cleaners may have the potential to emit it, and states that at concentrations which do not exceed public health standards ozone has little potential to remove indoor air contaminants, while when inhaled it can damage the lungs.
California requires portable indoor air cleaners sold in the state to be certified against an ozone emission limit of 0.050 ppm and publishes the certified list, which EPA points readers at. Read that list correctly. CARB says its certification does not reflect an air cleaner's effectiveness — it is a floor on ozone emission, nothing more. Use it to rule units out. Never use it to rule one in.
On what to expect, in EPA's own words rather than ours. EPA's summary of the research on portable HEPA air cleaners is deliberately modest: studies have found improvements in one or more allergy or asthma symptoms, and improvements in cardiovascular and respiratory measures that are typically small and not always noticeable to the individual. We repeat that here because it is the sentence marketing removes. If you have a specific health concern during a smoke event, that is a conversation with a clinician and with your local health authority, not with a specification sheet.
Every figure above is reproduced from one of these. Nothing here is our own determination about air quality, and the one piece of arithmetic that is ours — dividing EPA’s own table down to a per-square-foot rate — is labelled as ours where it appears.