A compact and portable liquid concentrator includes a gas inlet, a gas exit and a flow corridor connecting the gas inlet and the gas exit, wherein the flow corridor includes a narrowed portion that accelerates the gas through the flow corridor. Since it is possible to detect the distribution of the collection amount of PMs with good accuracy, it is possible to carry out a recycling process in a state where the collection amount does not become too much, and thereby it is possible to make a reducing-agent supply amount into exhaust gases minimum at the time of the recycling process. Each of the disclosed embodiments includes at least one of either an adjustable seat, an adjustable footrest, a center post mounted tray, a multiple position, single-hand adjustable tray, a concealed release button, and any combination of such features.