A portable air-filtering device , the air-filtering device being configured to be arranged in association with a top end of a baby-transporting device , said top end being a part of the baby transporting device where a baby's head is positioned, or a part close to or directly adjacent to a part where the baby's head is positioned, wherein the air-filtering device comprises: an air-impermeable back layer ; an air-permeable front layer arranged opposite to the back layer , wherein the air-filtering device is configured to be arranged with the front layer directed towards an inner area (B) of the baby-transporting device ; said back layer and front layer being arranged to form an internal cavity there between; a first air inlet arranged in the back layer in fluid communication with the internal cavity ; a first power driven ventilator arranged to draw air from an external surrounding (A) through the first air inlet into the internal cavity , so that an overpressure is generated in the cavity ; wherein the air-filtering device comprises: an outer air filter arranged to cover the first air inlet ; a baffle arranged in the internal cavity to direct the air inside the internal cavity ; and an inner air filter arranged to face the inner area (B) of the baby-transporting device , wherein the inner air filter is adapted to remove microparticles having a size of 0.1-1000 μm from the air, wherein the overpressure in the internal cavity will force the air to flow through said front layer towards the inner area (B), wherein the front layer comprises a material configured such that the air will be evenly distributed within the front layer before exiting said front layer whereby the air will be evenly distributed through the inner air filter , thereby providing a local environment of purified air in the inner area (B) of the baby-transporting device . an air-impermeable back layer ; an air-permeable front layer arranged opposite to the back layer , wherein the air-filtering device is configured to be arranged with the front layer directed towards an inner area (B) of the baby-transporting device ; said back layer and front layer being arranged to form an internal cavity there between; a first air inlet arranged in the back layer in fluid communication with the internal cavity ; a first power driven ventilator arranged to draw air from an external surrounding (A) through the first air inlet into the internal cavity , so that an overpressure is generated in the cavity ; wherein the air-filtering device comprises: an outer air filter arranged to cover the first air inlet ; a baffle arranged in the internal cavity to direct the air inside the internal cavity ; and an inner air filter arranged to face the inner area (B) of the baby-transporting device , wherein the inner air filter is adapted to remove microparticles having a size of 0.1-1000 μm from the air, wherein the overpressure in the internal cavity will force the air to flow through said front layer towards the inner area (B), wherein the front layer comprises a material configured such that the air will be evenly distributed within the front layer before exiting said front layer whereby the air will be evenly distributed through the inner air filter , thereby providing a local environment of purified air in the inner area (B) of the baby-transporting device . <EOS>