Please answer a question about the following article about Airport:

Following the war, some of these military airfields added civil facilities for handling passenger traffic. One of the earliest such fields was Paris Le Bourget Airport at Le Bourget, near Paris. The first airport to operate scheduled international commercial services was Hounslow Heath Aerodrome in August 1919, but it was closed and supplanted by Croydon Airport in March 1920. In 1922, the first permanent airport and commercial terminal solely for commercial aviation was opened at Flughafen Devau near what was then Konigsberg, East Prussia. The airports of this era used a paved "apron", which permitted night flying as well as landing heavier aircraft.

When did the Hounslow Heath Aerodrome begin to operate scheduled international commercial services?
August 1919