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Related Clues:
- This puzzle's theme source
- One of the greenhouse gases
- Stratosphere substance
- Colourless gas, O3
- Short-supply item, in a drought
- 48 Across, essentially
- Layer with "holes" in it
- Plain dinner quaff
- Need for life
- Triatomic oxygen molecule
- Moisten, as a lawn
- Oasis refreshment
- Triatomic gas in a thinning layer ... and, symbolically, what appears in this puzzle's four longest answers
- *Tend to the garden
- Gas that screens ultraviolet radiation