What this site does not cover, and why

The rule we are following

Every ActSmall topic operates on a single editorial rule: where the named public-health and atmospheric-science authorities converge, we display it; where they diverge or are silent, we do not invent a position. The named bodies for ambient air quality are the World Health Organization (WHO), the US Environmental Protection Agency (EPA), the European Environment Agency (EEA), and the Intergovernmental Panel on Climate Change (IPCC). Where those bodies have published clear positions, we cite them. Where they have not, we say nothing.

"Chemtrails" and aircraft contrails

Aircraft exhaust contains real, measurable particulate matter and the contrails (water-ice condensation trails) themselves have a real radiative-forcing effect on climate — the IPCC AR6 working group covers contrail cirrus in chapter 7, and the EU's Clean Sky programme funds work on hydrogen and sustainable-aviation-fuel pathways^[1]. None of this is the "chemtrail" claim. The chemtrail claim is that contrails are a deliberate aerial-dispersal program of chemical or biological agents. There is no public-health body, anywhere, that has documented this; the WHO, EPA, EEA, and every major atmospheric-science academy have published explicit rejections^[2]. We do not have a contrail layer on the air-quality map because the real signal (aviation NOx and particulate emissions over flight corridors) is a regulatory-aviation topic, not an individual-household action.

Ionizing air purifiers and ozone generators

Consumer air-purification devices that use corona discharge, plasma, or "ionizers" to electrostatically capture or oxidize indoor pollutants are a real product category. The US EPA's published position is unambiguous: these devices produce ozone as a by-product, and ozone is itself a regulated pollutant that the same EPA's National Ambient Air Quality Standards explicitly limit because it is harmful to the respiratory system^[3]. The California Air Resources Board maintains a list of certified versus uncertified air cleaners under California Health and Safety Code 41986, specifically to keep ozone-generating devices off store shelves^[4]. We do not promote brand-specific ionizers or "active" air cleaners for the same reason — the EPA, CARB, and ASHRAE all converge on the same position, and we follow it. Where readers want a cleaner-air device, we name HEPA-filtration mechanical purifiers (passive, no oxidation chemistry) and the open-source Corsi-Rosenthal box, both of which are recommended by the same agencies^[5].

Essential-oil diffusers, "air fresheners", and indoor VOCs

Essential-oil diffusers and conventional air-freshener products release volatile organic compounds (VOCs) into the indoor air; some of those VOCs (notably limonene and pinene) react with indoor ozone to form secondary particulate matter and formaldehyde. This is well-documented in the indoor-air-quality literature, and the EPA's Indoor Air Quality programme covers it^[6]. What we do not say is that any particular essential oil "purifies", "antimicrobial-treats", or "boosts respiratory health". There is no peer-reviewed clinical evidence the WHO, EPA, or any national public-health authority has endorsed for those claims at consumer exposures, and we treat them the same way we treat any other unproven health claim — we do not repeat them.

Brand-by-brand air purifier rankings

"What is the best air purifier" is the most-asked consumer question in this topic. We do not answer it with brand names. The reason is structural: HEPA-filtration efficiency, CADR (Clean Air Delivery Rate), and Energy Star certification are objective specifications that the EPA, AHAM, and Energy Star programmes publish openly — we link to those resources directly. A current "best brand" list goes out of date in months and creates a perceived endorsement we cannot stand behind globally. Consumer-Reports-style brand comparisons exist; they are paywalled in many regions, US-centric, and not appropriate as the canonical reference for a globally-readable site. We name the specifications to look for and link to the named certifiers' product-finder tools.

Solar radiation management and stratospheric aerosol injection

Stratospheric aerosol injection (SAI) and marine cloud brightening are real geoengineering proposals under active scientific study; the National Academies of Sciences, Engineering, and Medicine published a 2021 consensus report on the research framework, and the IPCC AR6 chapter 4 covers them as a class^[7]. We do not have a "geoengineering" layer on the map because no SAI deployment exists at any meaningful scale and the topic does not produce an individual-household action. Where the SAI research community publishes new findings we link to the named institutional source rather than repeating media summaries.

Indoor radon and household-radiation topics

Indoor radon is a real indoor-air-quality issue and it is the second leading cause of lung cancer after smoking, per the WHO and IARC. We do not cover it on the air topic because it has its own ActSmall topic at ground.actsmall.org, where the dose-budget, soil-gas, and household-test-kit content lives. The air topic stays scoped to ambient and indoor combustion-particle pollutants — PM2.5, PM10, NO₂, ozone, SO₂, and selected indoor VOCs.

Where this leaves us

The air topic covers what the WHO, EPA, EEA, and IPCC have converged on: ambient and indoor particulate matter, the WHO 2021 Air Quality Guidelines, the OpenAQ measurement network, the WHO/Health Effects Institute State of Global Air, and the practical indoor-air actions (HEPA, Corsi-Rosenthal, low-emission cooking, ventilation) that those agencies recommend. Where the named authorities are silent or have explicitly said "no public-health story", we say the same.