**Houseplants can absorb some pollutants, but ordinary numbers of them won’t meaningfully clean your apartment’s air.** Get them because you enjoy them; investigate the headaches separately.

The quantitative evidence answers your “small forest” question. A review of 12 studies found that plants removed volatile organic compounds in small sealed chambers, but very slowly. Matching the pollutant removal provided by typical building ventilation would require approximately **10–1,000 plants per square metre**. Your 670-square-foot apartment is about 62 m²: that translates to roughly **620–62,000 plants**. This is a comparison with ventilation, not a prescription or a guarantee of healthy air. [Cummings and Waring, 2020](https://researchdiscovery.drexel.edu/esploro/outputs/journalArticle/Potted-plants-do-not-improve-indoor/991019168419404721)

**The headaches deserve attention before experimenting with air cleaners.** Carbon monoxide is odorless and can cause headaches. Make sure you have working CO alarms, particularly if the building has fuel-burning heating, water heaters, or cooking appliances. If an alarm sounds—or you suspect CO because of headaches with dizziness, nausea, weakness, or other occupants becoming ill—get outside immediately and seek emergency help. A recurring headache associated with the apartment also warrants medical advice. [CDC guidance](https://www.cdc.gov/carbon-monoxide/about/)

For the apartment, I’d proceed in this order:

1. **Have the landlord check ventilation and possible sources.** The fact that closing the windows triggers the problem makes inadequate fresh-air exchange worth investigating, though it doesn’t identify the cause. Ask about functioning exhaust fans, outdoor-air provision, combustion appliances, and dampness. Many residential heating and cooling systems simply recirculate indoor air. Ventilate with clean outdoor air when conditions allow. [EPA guidance](https://www.epa.gov/indoor-air-quality-iaq/improving-indoor-air-quality)

2. **Use a HEPA purifier if dust or other particles are a concern.** It can remove airborne particles; it won’t supply fresh air or resolve CO₂ buildup. For a single open 670-square-foot space with an eight-foot ceiling, extrapolating EPA’s sizing table gives a particle CADR of approximately **435 cubic feet per minute**. Separate bedrooms may need separate units. Check CADR and noise at the speed you’ll actually use, rather than relying on advertised coverage alone. [EPA air-cleaner guide](https://www.epa.gov/indoor-air-quality-iaq/guide-air-cleaners-home)

3. **Treat gases as a different problem.** HEPA doesn’t remove formaldehyde or other gases. Gas filtration requires suitable adsorbent media; EPA notes that activated carbon works best when there is a substantial amount of it. A thin carbon sheet offers limited capacity. Avoid devices that intentionally generate ozone. [EPA air-cleaner guide](https://www.epa.gov/indoor-air-quality-iaq/guide-air-cleaners-home)

A genuine **NDIR CO₂ monitor** can help you see whether ventilation is poor while the apartment is occupied. It measures a ventilation indicator, not overall air safety, and it cannot detect carbon monoxide or formaldehyde. [HSE guidance on CO₂ monitoring](https://www.hse.gov.uk/ventilation/using-co2-monitors.htm)

The flooring and ceiling are clues, but neither establishes the cause:

- **Laminate flooring:** Some products emit formaldehyde, with emissions depending on the product, temperature, humidity, and ventilation. Five weeks without improvement doesn’t rule out continuing emissions. If symptoms persist, seek a building assessment and targeted testing rather than assuming formaldehyde is responsible. [EPA laminate-flooring guidance](https://www.epa.gov/formaldehyde/questions-and-answers-regarding-laminate-flooring)
- **Popcorn ceiling:** Older textured ceilings may contain asbestos. Leave an intact ceiling undisturbed; if it is crumbling or shedding, report it and arrange professional assessment before scraping or sampling it. [EPA asbestos guidance](https://www.epa.gov/asbestos/protect-your-family-exposures-asbestos)

A purifier is much more realistic than plants for reducing dust, but **checking CO and getting the ventilation assessed are the priorities given your headaches**.