This　paper　reports　the　use　of　LIDAR　technique,　vertical　wind　profiler　(VWP)　and　the　coupled　MM5-CMAQ　air　quality　modeling　system　to　investigate　a　high　PM10　concentration　episode　occurred　in　Beijing,　China　during　January　8-9,　2004.　Through　the　regression　analysis　between　the　observed　PM10　concentrations　and　the　observed　extinction　coefficients,　the　converting　formulas　from　the　LIDAR　records　to　the　PM10　mass　concentrations　in　Beijing　have　been　found.　Further,　a　2-level-nested　grid　domain　with　spatial　resolutions　of　36　and　12　km　have　been　designed　and　employed　for　this　study,　and　the　coupled　MM5-CMAQ　modeling　system　has　then　been　evaluated　using　both　the　ground-level　PM10　observations　and　the　vertical　profiles　of　PM10　deduced　from　the　measured　LIDAR　extinction　coefficients.　Based　on　the　verified　modeling　system,　two　emission　scenarios　were　designed　to　quantitatively　assess　the　trans-boundary　PM10　contributions　from　the　surrounding　provinces　of　Beijing.　The　results　illustrated　that　the　particulate　matter　buildup　over　the　Beijing　region　was　due　to　a　number　of　factors,　including　pollutants　brought　in　from　its　surrounding　provinces　by　the　southwest　winds　and　the　emission　from　local　sources　within　Beijing.　It　indicates　that　while　Beijing　needs　to　take　positive　steps　to　reduce　its　own　pollution　emissions,　much　effort　should　also　be　placed　on　demanding　more　pollution　reduction　and　better　environmental　performance　from　its　surrounding　provinces.