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. Ambient particulate matter (PM) can contain a mix ofdifferent toxic species derived from a wide variety of sources. This studyquantifies the diurnal variation and nocturnal abundance of 16 polycyclicaromatic hydrocarbons (PAHs), 10 oxygenated PAHs (OPAHs) and 9 nitrated PAHs(NPAHs) in ambient PM in central Beijing during winter. Target compoundswere identified and quantified using gas chromatography–time-of-flightmass spectrometry (GC-Q-ToF-MS). The total concentration of PAHs variedbetween 18 and 297 ng m −3 over 3 h daytime filter samples and from 23to 165 ng m −3 in 15 h night-time samples. The total concentrations ofPAHs over 24 h varied between 37 and 180 ng m −3 (mean: 97±43  ng m −3 ).The total daytime concentrations during high particulate loadingconditions for PAHs, OPAHs and NPAHs were 224, 54 and 2.3 ng m −3 ,respectively. The most abundant PAHs were fluoranthene (33 ng m −3 ),chrysene (27 ng m −3 ), pyrene (27 ng m −3 ), benzo[a]pyrene (27 ng m −3 ), benzo[b]fluoranthene (25 ng m −3 ), benzo[a]anthracene (20 ng m −3 ) and phenanthrene (18 ng m −3 ). The most abundant OPAHs were9,10-anthraquinone (18 ng m −3 ), 1,8-naphthalic anhydride (14 ng m −3 ) and 9-fluorenone (12 ng m −3 ), and the three most abundantNPAHs were 9-nitroanthracene (0.84 ng m −3 ), 3-nitrofluoranthene (0.78 ng m −3 ) and 3-nitrodibenzofuran (0.45 ng m −3 ). ∑ PAHs and ∑ OPAHs showed a strong positive correlation with the gas-phaseabundance of NO, CO, SO2 and HONO, indicating that PAHs and OPAHs canbe associated with both local and regional emissions. Diagnostic ratiossuggested emissions from traffic road and coal combustion were thepredominant sources of PAHs in Beijing and also revealed the main sourceof NPAHs to be secondary photochemical formation rather than primaryemissions. PM2.5 and NPAHs showed a strong correlation with gas-phaseHONO. 9-Nitroanthracene appeared to undergo a photodegradation during thedaytime and showed a strong positive correlation with ambient HONO( R=0.90 , P  ). The lifetime excess lung cancer risk for thosespecies that have available toxicological data (16 PAHs, 1 OPAH and 6 NPAHs)was calculated to be in the range 10 −5 to 10 −3 (risk per millionpeople ranges from 26 to 2053 cases per year).

Variability of polycyclic aromatic hydrocarbons and their oxidative derivatives in wintertime Beijing, China