Biomass burning is a major source of atmospheric aerosols on both global and regional scales. Among the large number of unidentified organic compounds related to biomass burning, the nitrogen-containing aromatic compounds (NACs) have drawn attention due to their UV light-absorbing ability. Some of the NACs can also serve as organic tracer compounds for secondary organic aerosols (SOA) formed from biomass burning. In this study, an analytical method based on liquid chromatography/mass spectrometry was used to quantify a group of NACs (nitrophenol (4NP), methylnitrophenols (MNPs), dimethylnitrophenol, nitrocatechol (4NC), and methylnitrocatechols (MNCs) in aerosol samples. The nitrocatechol-metal complex interference, sample matrix effects, sample stability, precision, and reproducibility...[ Read more ]

Biomass burning is a major source of atmospheric aerosols on both global and regional scales. Among the large number of unidentified organic compounds related to biomass burning, the nitrogen-containing aromatic compounds (NACs) have drawn attention due to their UV light-absorbing ability. Some of the NACs can also serve as organic tracer compounds for secondary organic aerosols (SOA) formed from biomass burning. In this study, an analytical method based on liquid chromatography/mass spectrometry was used to quantify a group of NACs (nitrophenol (4NP), methylnitrophenols (MNPs), dimethylnitrophenol, nitrocatechol (4NC), and methylnitrocatechols (MNCs) in aerosol samples. The nitrocatechol-metal complex interference, sample matrix effects, sample stability, precision, and reproducibility were investigated and reported. The method detection limits ranged from 0.10–0.23 ng/mL and the recoveries for the target NACs were in the range of 96–102%.

The method was applied to analyze a total of 184 ambient PM_2.5 samples collected at an urban site in Hong Kong over three years (2010–2012). The NACs quantified showed a distinct seasonal variation with higher concentrations in fall and winter (3.6–21.0 ng/m³), coinciding with more biomass burning activities coming from the western and northeastern region to Hong Kong, and lower levels during spring and summertime (0.3–3.8 ng/m³). The good correlations between NACs and levoglucosan (R²=0.67), a known biomass burning tracer compound, support the common origin from biomass burning. Moderate to good correlations between NACs and nitrate suggest that they might share the same precursor gases (e.g. NO_x) or similar formation pathways. Using the fraction of MNCs in the SOA mass of m-cresol oxidation derived in the chamber experiment (Iinuma et al., 2010), the m-cresol SOA in ambient PM_2.5 samples was estimated to be in the range of 0.04–260 ng/m³, revealing that the biomass burning SOA could make non-negligible contributions to the ambient OA in this region especially during wintertime.