I’d treat this as a two-part job: deal with the bird droppings first, then tackle the general city grime. Put on gloves, a mask, and eye protection before you start, because bird droppings can carry pathogens and you don’t want to breathe in dust or spray. Remove loose leaves and debris, then wet the droppings with warm soapy water or a soaked paper towel and let them soften for a few minutes. Don’t scrape them dry, since that can spread germs and scratch painted or powder-coated surfaces.
For the city grime—soot, exhaust film, pollen, and sticky residue—use a mild dish soap mixed with warm water and a soft brush or microfiber cloth. Work in small sections from top to bottom, and rinse your cloth often so you’re not just moving dirt around. If you hit a greasy patch, try a small amount of a gentle degreaser that’s safe for the material, but test it on a hidden spot first. For sticky spots on metal or plastic, a baking soda paste can help; rinse it thoroughly afterward.
Rinse everything with a garden hose on low pressure. Avoid a pressure washer on wood, woven furniture, fabric seams, and painted metal, because it can force water into joints and strip finishes. For hard, nonporous surfaces, you can follow up with a disinfectant labeled for outdoor use and let it sit for the recommended contact time. Don’t mix bleach with ammonia, vinegar, or other cleaners. For fabric cushions, check the care label, use an outdoor fabric cleaner, rinse well, and let them dry completely in the sun or a ventilated area.
Dry the furniture fully before using or covering it. Once it’s dry, protect wood with an appropriate outdoor sealant, wipe metal joints and moving parts, and use a UV protectant on plastic if the manufacturer recommends it. In a city, spot-clean droppings as soon as you see them, rinse weekly during dirty seasons, and do a deeper clean monthly or before entertaining. That routine keeps the furniture looking better and stops grime from turning into a permanent finish problem.