Abstract

Airborne nitrated polyaromatic hydrocarbons (NPAHs) are of public health concern due to their higher genotoxicity than parent PAHs.1,2 They are also constituents of brown carbon.3,4 Their ambient presence characterization and sources are much less studied than the unsubstituted PAHs. We investigated NPAHs in sixty PM2.5 samples collected in Hong Kong over one-year period. Quantitative and semiquantitative analysis of NPAHs were conducted using in-injection port thermal desorption coupled with gas chromatography/mass spectrometry (GC/MS) under negative chemical ionization mode. NPAHs that do not have authentic standards were identified based on the joint evaluation of three GC/MS features: 1) retention time, 2) mass spectrum profile, and 3) monitored ion pair (i.e., M– & M+1–). A total of 27 NPAHs in 9 formula groups were detected, categorized into 2-, 3-, and 4-ring NPAHs. Three formula groups are dinitro-PAHs, one each in 2-, 3-, and 4-ring NPAH categories. NPAHs with 4 and 3 rings took up a dominant percentage in the summed amount of all NPAHs. In Hong Kong, the total NPAH concentration was significantly higher in winter than in summer, which was most likely attributed to the seasonally varied meteorological conditions (e.g., temperature, monsoon) and anthropogenic combustion activities. Taking advantage of available molecular and elemental tracers for common combustion sources, we found vehicle emission and coal combustion were likely the two most important primary sources for NPAHs in PM2.5. Results from this work are useful in gauging the relative importance of different groups of NPAHs and in shedding insight into the possible origins of NPAHs. The semi-quantified NPAH data could also serve as a reference for the future complementary analysis.

Reference:

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