Size, spatial distribution, and diurnal variations of particulate nitrophenols in the central Yangtze River Delta,...

In this study, paired integrated PM_2.5 and PM₁₀ samples, as well as time-resolved PM_2.5 samples, were collected during summer and winter from two sampling campaigns in northern Nanjing, China. Synchronous wintertime PM_2.5 samples from five urban sites in the center of the Yangtze River Delta (YRD), China, were retrieved from another campaign. Four nitrophenols (NPs)-4-nitrophenol (4NP), 3-methyl-4-nitrophenol (3M4NP), 2-methyl-4-nitrophenol (2M4NP), and 4-nitrocatechol (4NC)-were speciated in each sample. The concentrations of individual NPs in PM_2.5 and PM₁₀ were significantly correlated (r > 0.70, p < 0.05), and the majority (>70 %) of the four NPs were present in fine particles. All NPs showed similar temporal variations across the five urban sites in winter (r = 0.68 ± 0.15-0.78 ± 0.066, p < 0.05), with 4NC exhibiting the least spatial variability. The diurnal variations of PM_2.5-bound 4NP, 3M4NP, and 2M4NP in winter showed two elevations during 8:00-14:00 and 16:00-2:00 (next day), likely dominated by the photooxidation of gaseous aromatics and nighttime NO₃‧ chemistry, respectively. In summer, their diurnal patterns were characterized by a sharp increase during 16:00-20:00 and rapid removal after 20:00, which may correspond to NP formation from newly emitted precursors during rush hour and NO₃‧-initiated degradation at night. The diurnal variations of 4NC were similar to those of anhydrosugars in winter and secondary sulfate in summer. By combining measurement data of NPs and source tracers in PM_2.5, positive matrix factorization (PMF) was conducted to evaluate NP sources. A secondary NP production factor was identified as the largest contributor to total NPs in time-resolved samples for both summer (71.4 %) and winter (39.3 %). The biomass burning factor contributed significant fractions of NPs in all winter samples, particularly for 4NC (>80 %).