Heavy metals in ambient air rarely occur elementary but most of the time bound to particulate matter. By inhalation health risks arise because some pollutants like arsenic, cadmium and nickel are classified to be cancerogenic.
The European directive 2004/107/EC regulates the measurement and assessment of arsenic, cadmium and nickel in particulate matter (PM10).
Lead in particulate matter (PM10) has been measured for a longer time. It is regulated in the European directive 2008/50/EC.