Hello, this is Dr. David. I have read your question and am ready to help.
Ammonia is what is bothering him in the cat's urine. Ammonia is a primary eye and upper respiratory tract irritant. OSHA found that a 5-minute ceiling limit for ammonia of 50 ppm is even too much. even 5-minute exposures to 32 ppm caused nasal dryness in 10 percent of exposed volunteers, and that 5-minute exposures to 50 ppm ammonia caused nasal irritation and dryness in 20 percent of exposed volunteers.
Ammonia has not been classified as a carcinogen, however, if something is a chronic exposure and causes enough irritation for long enough periods of time, it can increase the risks for cancer if mixed with other carcinogens like smoking, or polution exposure, etc.
have him read these about ammonia
is he willing to have you pay for a cat litter cleaning service which can come to his house 1-2 times a week and change the cat litter?