An exhaust gas treatment system is provided with: a desulfurization device (105) which removes sulfur oxide in the exhaust gas (11) from a boiler (101); a cooling tower (70A) which is provided downstream of the desulfurization device (105) and which reduces the temperature of the exhaust gas (11) by cooling or heating the exhaust gas (11) and increasing the diameter of the particles of SO3 mist contained in the exhaust gas (11), the cooling or heating of the exhaust gas (11) being performed by a temperature regulation means for regulating the gas dew point temperature of the exhaust gas (11); and a CO2 recovery device (10) which is constructed from a CO2 absorption tower (13) for removing CO2 in the exhaust gas (11) by bringing the CO2 into contact with a CO2 absorption liquid, and also from a regeneration tower (14) which recovers CO2 by releasing CO2 from the CO2 absorption liquid and which regenerates the CO2 absorption liquid (12). A cooling section (70a) cools the exhaust gas (11) and increases the size of the SO3 mist in the exhaust gas.
