Black　carbon　(BC)　aerosol　plays　an　important　role　in　climate　forcing.　The　net　radiative　effect　is　strongly　dependent　on　the　physical　properties　of　BC　particles.　A　single　particle　soot　photometer　and　a　carbon　monoxide　analyser　were　deployed　during　the　Chinese　Lunar　Year　(CLY)　and　on　weekdays　at　Xi＇an,　China,　to　investigate　the　characteristics　of　refractory　black　carbon　aerosol　(rBC).　The　rBC　mass　on　weekdays　(8.4　mu　g　center　dot　m(-3))　exceeds　that　during　the　CLY　(1.9　mu　g　center　dot　m(-3)),　presumably　due　to　the　lower　anthropogenic　emissions　during　the　latter.　The　mass　size　distribution　of　rBC　shows　a　primary　mode　peak　at　~205　nm　and　a　small　secondary　mode　peak　at　~102-nm　volume-equivalent　diameter　assuming　2　g　center　dot　cm(-3)　in　void-free　density　in　both　sets　of　samples.　More　than　half　of　the　rBC　cores　are　thickly　coated　during　the　CLY　(f(BC)　=　57.5%);　the　percentage　is　slightly　lower　(f(BC)　=　48.3%)　on　weekdays.　Diurnal　patterns　in　rBC　mass　and　mixing　state　differ　for　the　two　sampling　periods,　which　are　attributed　to　the　distinct　anthropogenic　activities.　The　rBC　mass　and　CO　mixing　ratios　are　strongly　correlated　with　slopes　of　0.0070　and　0.0016　mu　g　center　dot　m(-3)center　dot　ppbv(-1)　for　weekdays　and　the　CLY,　respectively.