The right professional to contact about a persistent odor depends on the nature and location of the smell.
If you suspect a gas leak, contact your utility company immediately. Gas leaks are dangerous and require immediate attention.
If the smell is coming from a specific appliance or fixture in your home, you may want to contact a qualified professional to inspect and repair the appliance or fixture.
If the smell is coming from outside your home, you may want to contact your local health department or environmental agency. These organizations can investigate the source of the odor and take appropriate action to address it.