Open burning of waste is illegal (EMCA 1999 and the Air Quality Regulations, fines up to KSh 1M and beyond). Most complaints fail because they lack the details officials can act on. Fill this in; it writes a proper complaint addressed to the right offices. Nothing you type leaves your device until you press send in your own email app.
Landmark + road + area. Add GPS coordinates if you can (long-press the spot in Google Maps).
Photos with the phone's date/location are strong evidence. Attach them after your email app opens.
Also send a copy to the Atmos Nairobi public tally (atmosnairobi@gmail.com). We count complaints and, later, publish how many got a response. Your complaint, our receipt-keeping.
Where this goes: NEMA incidents (incidence@nema.go.ke, hotline 0786 101 100 / 0741 101 100) and Nairobi City County environment department. The law you are citing: Environmental Management and Co-ordination Act s.87 (prohibits waste burning without a licence) and the Air Quality Regulations open-burning prohibition. You do not need a lawyer to complain; you need the location, the time, and persistence. If nothing happens, complain again and keep your reference numbers.