Pollen　allergy　has　become　a　major　problem　for　a　considerable　and　steadily　increasing　percentage　of　people　worldwide.　Allergenic　protein,　which　is　contained　in　subpollens,　can　be　released　from　pollen　and　suspended　in　air　to　cause　allergenic　reactions.　However,　the　distribution　of　the　allergenic　protein　and　its　relationship　with　inorganic　ions　in　ambient　particles　has　not　been　reported.　Here,　a　recombinant　Platanus　acerifolia　allergen3　and　tandemsix-histidine　epitope　(His(6))　fusion　protein　(rPla　a3)　was　expressed　in　a　prokaryotic　system　and　then　purified　by　affinity　chromatography.　The　allergenicity　of　both　rPla　a3　and　natural　Pla　a3　in　Platanus　pollen　protein　extract　was　assessed　by　enzyme-linked　immunosorbent　assay　using　the　sera　of　rPla　a3-sensitized　rats.　Our　results　demonstrated　that　IgE　from　rPla　a3-sensitized　rats　could　be　used　to　quantify　the　allergenicity　of　Pla　a3　in　the　released　Platanus　pollen　and　identify　the　mass　level　of　Pla　3　in　size-resolved　particles.　The　peak　of　natural　Pla　a3　expression　was　found　in　the　middle　of　April,　and　the　highest　mass　level　of　Pla　a3　occurred　in　ambient　particles　diameters　larger　than　7　mu　m.　The　mass　concentration　of　Pla　a3　in　the　atmosphere　was　consistent　with　that　of　the　total　protein　variety,　which　also　showed　a　peak　in　particles　with　diameters　larger　than　7　mu　m　during　the　Platanus　pollen　season.　Remarkably,　most　Pla　a3　existed　in　particulate　matters　＞　7　mu　m,　including　intact　Platanus　pollen,　and　non-negligible　partitions　of　Pla　a3　were　detected　in　particles　with　diameters　less　than　7.0　mu　m.　Major　ions　(Ca2+,　NH4+,　and　SO42-)　in　ambient　particles　not　only　aggravated　pollen　rupture　and　content　release,　but　also　affected　the　distribution　of　Pla　3　in　the　particles.　Allergic　disease　could　be　specifically　identified　by　using　rPla　a3,　and　there　was　a　short　lag　between　hospital　admission　for　allergic　disease　and　the　peak　of　Platanus　protein　concentration　in　spring.