A method of delivering a volatile material to the atmosphere in a continuous manner is disclosed. The method includes providing a delivery engine having a reservoir that includes a volatile material mixture. The volatile material mixture includes about 40% to about 100%, by total weight, of the volatile materials each having a vapor pressure at 25°C of less than about 0.1 torr. The delivery system also includes a microporous membrane enclosing the reservoir, wherein the microporous membrane comprises an average pore size of about 0.01 to about 0.03 microns.