The　contradiction　between　urban　density　and　sustainable　environmental　development　is　increasingly　prominent.　Although　numerous　studies　have　examined　the　impact　of　urban　density　on　air　pollution　at　the　macro　level,　most　previous　research　at　the　micro　scale　has　either　neglected　socioeconomic　factors,　failed　to　analyze　heterogeneous　effects,　or　ignored　historic　neighborhoods　where　high　pollution　coexists　with　high　density.　By　considering　population,　commercial　buildings,　vegetation,　and　road　factors,　an　integrated　social-biophysical　perspective　was　introduced　to　evaluate　how　urban　density　influences　PM2.5　concentration　in　a　historic　neighborhood.　The　study　area　was　divided　into　56　units　of　120　m　x　150　m　granularity,　as　determined　by　the　precision　of　the　LBS　population　data.　The　lasso　regression　and　quantile　regression　were　adopted　to　explore　the　main　factors　affecting　PM2.5　and　their　heterogeneous　effects.　The　results　showed　that　(1)　building　density　was　the　most　important　driving　factor　of　pollutants.　It　had　a　strong　and　consistent　negative　effect　on　PM2.5　concentrations　at　all　quantile　levels,　indicating　the　homogeneity　effect.　(2)　Short-term　human　mobility　represented　by　the　visiting　population　density　was　the　second　main　factor　influencing　pollutants,　which　has　a　significantly　positive　influence　on　PM2.5.　The　heterogeneous　effects　suggested　that　the　areas　with　moderate　pollution　levels　were　the　key　areas　to　control　PM2.5.　(3)　Vegetation　Patch　Shape　Index　was　the　third　main　factor,　which　has　a　positive　influence　on　PM2.5,　indicating　the　complex　vegetation　patterns　are　not　conducive　to　PM2.5　dispersion　in　historic　neighborhoods.　Its　heterogeneous　effect　presented　a　curvilinear　trend,　peaking　at　the　50th　quantile,　indicating　that　moderately　polluted　areas　are　the　most　responsive　to　improvements　in　vegetation　morphology　for　PM2.5　reduction.　These　findings　can　provide　effective　support　for　the　improvement　of　air　quality　in　historical　neighborhoods　of　the　city＇s　central　area.