https://larsschnellsblogg.blogspot.com/2025/11/the-eu-road-vehicle-fleet-emits.html
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Relative Humidity and Local Dehumidification
Relative humidity depends on temperature and available moisture. For example, air at 0°C can hold a maximum of 4.8 grams of water vapor per cubic meter, while air at +20°C can hold 17.3 grams per cubic meter. The mobility of air in the atmosphere is so extensive that local dehumidification does not noticeably dry out an area unless the dehumidifiers cover hundreds of square kilometers.
ChatGPT: Local dehumidification does not permanently dry out the surrounding environment. The atmosphere's vast volume and high mobility restore humidity through:
- Airflows (winds): Moist air quickly compensates for local deficits.
- Evaporation from soil and vegetation: Especially in warm areas, new water vapor continuously replenishes the air.
- : Air circulation on regional and global scales maintains a more balanced humidity over time.
Unless dehumidification occurs on an enormous scale (hundreds of km²), the air will be replenished with moisture from the surroundings. The atmosphere has a rapid recovery capacity for water vapor.
Summary:
- Removing water from the air locally does not affect the global moisture balance.
- No long-term local drying is noticeable if dehumidification is done on a reasonable scale.
Methods for Harvesting Moisture in Arid Areas
Deserts contain more humidity than expected, especially at night when temperatures drop and approach the dew point. Cost-effective methods to harvest this moisture include:
-
Dew Collectors (Radiative Coolers/Dew Ponds):
- Structures that cool overnight by radiating heat into space.
- Cools below the dew point → water condenses and is collected.
- Passive system; requires no energy.
- Optimal in deserts with clear night skies.
- Example: "Dew Bank" and .
-
Fog Nets (Fog Harvesters):
- Effective in fog-prone areas, such as coastal deserts (Atacama, Namib).
- Nets capture moisture from fog, which condenses into droplets.
- Low investment and minimal operating costs.
-
Solar-Powered Atmospheric Water Generators:
- Active systems that draw air through a condenser.
- Solar energy powers heating or cooling (used to regenerate sorbents or drive compressors).
- Suitable for areas with high solar radiation, like the Sahara.
-
:
- Materials that absorb water from the air at low humidity.
- Regenerated using solar heat during the day; water is collected at night.
- Promising for desert use, still under development.
-
:
- and release it when heated.
- Can be cycled using solar heat.
- Most cost-effective in desert environments.
Most Cost-Effective in Deserts:
- Passive dew collectors and sorbent-based systems with .
- These require little or no external energy and can be built with simple materials.
Efficiency of Moisture Harvesting Methods
| Method | Typical Yield (per unit) | Notes |
|---|---|---|
| Dew Collectors | 0.05–0.6 L/m²/night (theoretical max ~0.8 L/m²/night under ideal conditions) | Requires clear skies and significant nocturnal radiation. |
| Fog Nets | 1–10 L/m²/day (up to ~10–15 L/m²/day in dense fog) | Effective in foggy coastal areas. |
| Sorbent/MOF-Based Systems | ~2–4 L per kg of MOF/day at ~20% RH (higher in optimized units) | Yield depends on material density in the module. |
| Active Condensers (AWG) | Energy consumption: ~0.5–1.5 kWh per liter (yield: ~0.7–2 L/kWh in good conditions) | Higher energy cost per liter in very dry air. |
Humidity Differences: Desert vs. Meadow
At 20°C, saturated air holds ~17.3 g/m³ of water vapor. Typical absolute humidity levels (g/m³) for different relative humidity (RH) values:
| Location | RH (%) | Absolute Humidity (g/m³) |
|---|---|---|
| Desert | 10% | 1.73 |
| Desert | 20% | 3.46 |
| Desert | 30% | 5.19 |
| Meadow | 60% | 10.37 |
| Meadow | 70% | 12.10 |
| Meadow | 90% | 15.56 |
Differences:
- Desert (10% RH) vs. Meadow (60% RH): ~8.64 g/m³ less in desert air.
- Desert (10% RH) vs. Meadow (90% RH): ~13.83 g/m³ less.
Interpretation: Desert air typically contains ~1.7–5.2 g/m³ of water vapor, while humid meadow air contains ~10–15.6 g/m³. The difference is usually a few to over ten grams per cubic meter.
Practical Application: Irrigating a Tree in the Desert
Question: Is it meaningful to extract water from desert air to irrigate a tree? For example, can you plant a tree with a 10-meter free radius and water it using atmospheric moisture?
ChatGPT: Yes, extracting water from desert air can be meaningful if the technology is energy-efficient and locally optimized. Here’s why:
-
Feasibility:
- .
- Passive or solar-powered systems can operate without external energy.
- A can be created around a plant or cultivated area.
- Humidity increases slightly as temperatures drop at night.
-
Example: Tree with a 10-Meter Radius
- A young tree (e.g., acacia or moringa) requires ~20–40 liters of water per week.
- With a 10-meter radius (~314 m²), you can install passive dew plates or solar-powered sorbent modules.
- Realistic water production at 20°C and 20% RH:
- Passive condensation: ~0.05–0.2 L/m²/night.
- Sorbent-based systems: ~0.1–0.4 L/m²/day.
- With 314 m², you can theoretically collect:
- Passive dew: 16–62 L/night (under ideal conditions).
- Sorbent-based: 31–125 L/day.
-
Planting in a Circle:
- Create a circular, moisture-capturing surface (e.g., "pits" or mulch bowls) around the tree.
- Moist air condenses on specialized surfaces and flows toward the tree’s root zone.
- Advantage: and improved .
Conclusion: Yes, it is technically feasible to water a tree using atmospheric moisture in deserts, especially with:
- .
- Sorbent or MOF technology with solar regeneration.
- (e.g., a circle with a 5–15 meter radius).
- Critical: Isolate the water flow to the tree’s roots (e.g., using mulch or shading) to minimize evaporation losses.
https://larsschnellsblogg.blogspot.com/2025/11/the-eu-road-vehicle-fleet-emits.html
https://larsschnellsblogg.blogspot.com/2025/11/swedens-co-emissions-after-trees-co.html
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