| Temperature | With humidity it sets the dew point, the temperature at which air gives up its water. Anything colder than that, a duct, a diffuser, a wall next to a humid room, gets wet. | −40 to 85 °C · resolution 0.1 °C · accuracy ±0.5 °C | As every visit | ASHRAE 55-2023 |
- What it is
- How warm the air is, read in the middle of the room, away from the diffuser.
- Where it comes from here
- The thermostat setting, and how evenly it reaches each room. Rooms held at 20–22 °C under a humid ceiling void are common in Dubai villas.
- The line
- ASHRAE 55-2023 comfort range; our reports print 26 °C as the upper line.
- What you'd notice
- A room that feels cold and clammy at once; a bedroom that is comfortable at midnight and damp at 6 a.m.
- What moves it
- Temperature by itself is rarely the problem. It matters for what it does to the dew point, the next row, and for any surface colder than that: a duct, a diffuser, the back of a wardrobe on an outside wall. Anything below the dew point is wet.
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| Relative humidity | Held above 60% for long, ordinary surfaces grow mold with no leak at all. In a Gulf home it is the one number most worth watching. | 0 to 100% · resolution 0.1% · accuracy ±3% | As every visit | DM TG 142 (below 60%) |
- What it is
- How close the air is to holding all the water it can. 100% is fog. Read with temperature, it gives the dew point.
- Where it comes from here
- Outdoors, first: on the Gulf coast the outdoor dew point sits above 22 °C for a quarter of the year, and every open door, extract fan and gap in the walls and ceilings brings that air in. Then showers, cooking, and an air-conditioner that cools the room faster than it dries it. Source and method: Research Note 01
- The line
- Below 60%, ideally 30–50% (DM TG 142; TG 119 says the same).
- What you'd notice
- Nothing, at first: that is the point. 65% feels fine. Then a musty smell in a wardrobe, spotting behind a headboard, towels that never dry.
- What moves it
- Mold needs water, not a leak: above 60% for long enough, the water in the air is enough. Fixes are about drying the air (longer cooling run-time, dehumidification) and stopping the humid air getting in, which is what layer iv measures.
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| Air pressure | Which way air moves through the walls. A room at lower pressure than outside, every extract fan running, no fresh air coming in, pulls humid outdoor air in through every gap. | Differential manometer, one tube in the room and one outside it · 0 to 10,000 Pa · resolution 1 Pa · accuracy ±3 Pa up to 30 Pa | Barometric pressure only (300 to 1,100 hPa · ±1 hPa), for context; does not read room-to-room differences | practice criterion, direction only |
- What it is
- Whether the room is pushing air out or pulling it in, relative to outdoors and to the rooms next to it. We report the direction, not a limit; no guideline sets one, and we say so.
- Where it comes from here
- Every extract fan (bathroom, kitchen hood, dryer) pulls air out. If no fresh air is supplied to replace it, the whole flat goes negative and draws air in through every gap: from the corridor, the shaft, the outside.
- The line
- Practice criterion: direction only. A room pulling in humid outdoor air is the finding; the number is context.
- What you'd notice
- A door that slams or won't close; a draft at the skirting; a musty smell that arrives when the bathroom fan runs; dust lines at the edge of a door.
- What moves it
- Fresh-air supply matched to extract; sealing the paths air uses. This is the reading that most often explains why humidity is high in a room that has no leak.
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| Particulate matter (PM2.5) | Fine particles small enough to reach deep into the lungs: dust, traffic, construction, cooking. | 1 to 200 µg/m³ · resolution 1 µg/m³ · accuracy ±15 µg/m³ or ±10% of reading | 0 to 1,000 µg/m³ · ±5 µg/m³ up to 50, ±10% above | DM TG 119: 35 µg/m³ over 24 hours; 100 µg/m³ in any hour |
- What it is
- Particles smaller than 2.5 thousandths of a millimeter, small enough to pass the nose and throat and reach deep into the lungs. Counted by mass in the air.
- Where it comes from here
- Outdoors: dust, construction, traffic, the haze on a still day, brought in through the fresh-air intake and every gap. Indoors: cooking is the largest single source in most homes, and gas cooking more so; candles and incense follow.
- The line
- 35 µg/m³ over 24 hours; 100 µg/m³ in any hour (DM TG 119 Table 2).
- What you'd notice
- Mostly nothing: the particles that matter are invisible. Grey dust on the supply grilles and a film on dark furniture within a day of cleaning point to it.
- What moves it
- Filtration, in the right place: the filter grade in the air-handling unit, how well the fresh-air intake is filtered, a hood that actually vents outside. A portable purifier helps one room; the intake filter helps every room.
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| Total volatile organic compounds (TVOC) | The gases given off by paints, furnishings, cleaning products and fuels. | 0 to 30,000 ppb · resolution 1 ppb · accuracy ±20 ppb or ±15% of reading | 0 to 60,000 ppb · ±15% of reading | DM TG 119: 0.6 mg/m³ over 8 hours (0.3 for a new building) |
- What it is
- The sum of the gases given off by materials and products: hundreds of different compounds read as one number. Total, not identified: a high TVOC says something is off-gassing, not what. Where the what matters, a laboratory sample is the next step.
- Where it comes from here
- New paint, new joinery, new furniture and flooring: a fresh fit-out is a TVOC event that fades over weeks to months. Cleaning products, air fresheners, fuels stored in the garage. Heat and humidity both speed the release.
- The line
- 0.6 mg/m³ (600 µg/m³) over 8 hours for an existing building; 300 µg/m³ for a new one (DM TG 119 Tables 2 and 1).
- What you'd notice
- "New" smell that does not fade; headache or eye and throat irritation that lifts when you leave the building.
- What moves it
- Time and ventilation for a new fit-out; removing or containing the source otherwise. A TVOC reading is the one number on this page most changed by simply opening the space up for an hour before we arrive, which is why we ask you not to.
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| Carbon dioxide (CO₂) | The simplest measure of fresh air: people breathe it out, ventilation carries it away. Rising CO₂ means the room is not exchanging enough air for the people in it. | 400 to 10,000 ppm · resolution 1 ppm · accuracy ±50 ppm plus ±3% of reading | 400 to 10,000 ppm · ±30 ppm plus 3% of reading · dual-channel infrared (NDIR) | DM TG 119 (800 ppm, 8-hour; or 700 ppm above outdoor) |
- What it is
- The gas everyone in the room breathes out. Outdoors it is about 420 ppm; indoors it climbs with people and falls with fresh air. It is the simplest measure of how much outdoor air a room is getting.
- Where it comes from here
- People, in rooms that recirculate air without bringing fresh air in, which describes most Dubai bedrooms with the door shut and most meeting rooms by 11 a.m.
- The line
- 800 ppm over 8 hours, or 700 ppm above the outdoor level (DM TG 119 Table 2).
- What you'd notice
- Stuffiness; the mid-morning meeting-room headache; a bedroom that smells of sleep in the morning.
- What moves it
- Fresh air, full stop. At these levels CO₂ itself is not what harms you; it is a marker for everything else that builds up when a room is not ventilated: moisture, odors, the gases in the rows above. A high CO₂ reading sends the question to layer iv: is fresh air being supplied at all, and how much.
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| Carbon monoxide (CO) | An odorless combustion gas: generators, gas appliances, an attached garage. | 0 to 1,000 ppm · resolution 0.1 ppm · accuracy ±2 ppm or ±5% of reading | 0 to 1,000 ppm · ±1 ppm up to 20, ±5% above | DM TG 119: 9 ppm over 8 hours; 25 ppm in any hour |
- What it is
- A gas with no smell, produced whenever something burns without enough air. Small amounts feel like flu; more is dangerous.
- Where it comes from here
- A generator running near an intake; a gas water heater or cooker with a blocked flue; a car left running in an attached garage; a shisha or charcoal indoors.
- The line
- 9 ppm over 8 hours; 25 ppm in any hour (DM TG 119 Table 2).
- What you'd notice
- Headache, tiredness and nausea that several people share and that clear outdoors. Or nothing, which is why it is on the list.
- What moves it
- Finding and fixing the appliance, and venting it outside. A reading above the line is the one result on this page we telephone the same day.
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| Nitrogen dioxide (NO₂) | A combustion by-product: gas cooking, and traffic entering through the fresh-air intake. | 1 to 1,000 ppb · resolution 1 ppb · accuracy ±20 ppb or ±10% of reading | Not read by this monitor; taken with the visit instrument | DM TG 119: 0.1 ppm (200 µg/m³) in any hour; the annual 40 µg/m³ line cannot be read by a visit |
- What it is
- A sharp-smelling gas produced when fuel burns at high temperature: in a gas flame, or in a car engine.
- Where it comes from here
- Gas cooking without a hood that vents outside: a gas hob raises NO₂ in the kitchen within minutes and it spreads through the flat and lingers for hours. Outdoors, traffic, entering through a fresh-air intake that faces the road or the car park.
- The line
- 40 µg/m³ as a yearly average; 200 µg/m³ in any hour (DM TG 119 Table 2). A visit reads the hour.
- What you'd notice
- Irritated airways; asthma that is worse at home than elsewhere, or worse in the kitchen.
- What moves it
- A hood that vents outside (not a recirculating one), used every time the hob is lit; or moving from gas to induction. For an intake facing traffic, relocating or filtering it.
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| Ozone (O₃) | A reactive gas that irritates the airways, from some air purifiers and office machines, and from outdoors on hot, still days. | 1 to 1,000 ppb · resolution 1 ppb · accuracy ±20 ppb or ±10% of reading | Not read by this monitor; taken with the visit instrument | DM TG 119: 0.06 ppm over 8 hours; 0.12 ppm in any hour |
- What it is
- A reactive form of oxygen that irritates the airways. Useful high in the atmosphere; unwelcome at breathing height.
- Where it comes from here
- Indoors, some "ionising" or "ozone" air purifiers and older printers and copiers make it deliberately or as a by-product, and ozone then reacts with the gases in the TVOC row to make new compounds, some worse than what it started with. Outdoors, it forms in sunlight on hot, still days and comes in with the fresh air.
- The line
- 0.06 ppm (100 µg/m³) over 8 hours (DM TG 119 Table 2).
- What you'd notice
- A sharp "clean" or "electrical" smell near a device; a cough or chest tightness in the room where the purifier runs.
- What moves it
- Switching the device off is usually the whole fix. An air purifier that produces ozone is not cleaning your air; a good filter does not need to.
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Added by the extended monitor |
| Particulates by size (PM1, PM4, PM10) | PM2.5 says how much fine dust; the other sizes say what kind. Coarse PM10 is tracked-in and construction dust; PM1 is smoke and combustion. The split points to the source. | Extended monitor only | 0 to 1,000 µg/m³ each · ±5 µg/m³ up to 50, ±10% above | PM10: DM TG 119, 150 µg/m³ over 24 hours; 100 µg/m³ over 8 hours. PM1 and PM4: no guideline sets a line; reported for the pattern. |
| Formaldehyde | A gas given off by pressed-wood furniture, joinery, some flooring and finishes; strongest in a new fit-out, and faster in heat and humidity. | Extended monitor only | 0 to 2,000 ppb · ±30 ppb up to 300, ±10% above | DM TG 119 short-term line, 0.08 ppm over 30 minutes, indicative: the sensor's ±30 ppb cannot resolve the 8-hour line of 0.01 ppm |
| Light | Not an air reading. Recorded because it shows when a room is in use, which is what gives the air readings their context. | Extended monitor only | 0 to 40,000 lux · ±20 lux or ±5% | no guideline applied; context only |
| Sound | Recorded for the same reason, and because a noisy air-conditioning unit that is switched off at night is often the beginning of a humidity problem. | Extended monitor only | 30 to 120 dBA · ±3 dB | no guideline applied; context only |