The present invention provides a device for continuous real-time monitoring of ambient air. The device includes a receptacle, a liquid supply, and a pressure balancing system. The receptacle includes a gas inlet slit located such that the gas inlet slit is covered by liquid within the receptacle during use. The pressure balancing portion of the present device includes communication between a point within the receptacle above the liquid level in the receptacle, as well as a liquid inlet portion at the lowermost end of the receptacle, and an air space above a liquid supply portion and the liquid supply portion itself, respectively.