Metal sculptures exposed to outdoor environments face significant threats from acid rain and pollution, which can cause corrosion, discoloration, and structural damage over time. To preserve these artworks, several proven methods can be employed.

1. Apply Protective Coatings: Use specialized sealants like wax, lacquer, or clear acrylic coatings to create a barrier against moisture and pollutants. Reapply these coatings annually for optimal protection.

2. Choose Corrosion-Resistant Metals: Opt for metals like bronze, stainless steel, or corten steel, which naturally resist corrosion and require less maintenance.

3. Regular Cleaning: Gently wash sculptures with distilled water and a soft brush to remove acidic deposits. Avoid harsh chemicals that could strip protective layers.

4. Install Protective Structures: Consider placing sculptures under shelters, awnings, or glass enclosures to minimize direct exposure to rain and airborne pollutants.

5. Use Sacrificial Anodes: For large installations, attach zinc or magnesium anodes that corrode preferentially, diverting damage away from the sculpture.

6. Monitor Environmental Conditions: Track local pollution levels and rainfall acidity to adjust maintenance schedules accordingly.

By combining these strategies, artists and collectors can significantly extend the lifespan of outdoor metal sculptures while maintaining their aesthetic appeal. Regular inspections and prompt repairs of any damage are also crucial for long-term preservation.

For valuable pieces, consult professional conservators who can recommend customized protection plans based on the sculpture's material, location, and environmental challenges.