Elemental Composition of HULIS in the Pearl River Delta Region, China: Results Inferred from Positive and Negative Electrospray High Resolution Mass Spectrometric Data

Abstract

The HUmic-LIke Substances (HULIS) fraction isolated from aerosol samples collected at a rural location of the Pearl River Delta Region (PRD), China, during the harvest season was analyzed by both positive and negative mode electrospray ionization (ESI) coupled with an ultrahigh resolution mass spectrometer (UHRMS). With the remarkable resolving power and mass accuracy of ESI-UHRMS, thousands of elemental formulas were identified. Formulas detected in the positive (ESI+) and the negative (ESI-) mode complement each other due to differences in the ionization mechanism, and the use of both provides a more complete characterization of HULIS. Compounds composed of C, H, and O atoms were preferentially detected in ESI- by deprotonation, implying their acidic properties. Tandem MS and Kendrick Mass Defect analysis implies that carboxyl groups are abundant in the CHO compounds. This feature is similar to those of natural fulvic acids, but relatively smaller molecular weights are observed in the HULIS samples. A greater number of reduced nitrogen organic compounds were observed in the ESI+ compared to ESI-. Compounds with biomass burning origin including alkaloids, amino acids, and their derivatives are their probable constituents. Sulfur-containing species were dominantly detected in ESI-. The presence of sulfate fragments in the MS/MS spectra of these species and their high O/S ratios implies that they are mainly organosulfates. Organosulfates and nitrooxy-organosulfates were often the most intensive peaks in the ESI- spectra. They are believed to be products of reactive uptake of photooxidation products of reactive volatile organic compounds by acidic sulfate particles. The elemental compositions deduced from the UHRMS analysis confirm the conclusion from our previous study that biomass burning and SOA formation are both important sources of HULIS in the PRD region.

Molecular Characterization of Brown Carbon in Biomass Burning Aerosol Particles

“…45 The stability of the BrC chromophores was investigated by exposing the solutions of BBOA samples in 50% (v) water/ acetonitrile to filtered UV irradiation from a Xe-lamp and tracking the solution absorbance at 300 nm as a function of the The chemical composition of BBOA was investigated using the HPLC/HRMS data acquired in both positive (+) and negative (−) ESI modes. 50 Compounds were detected as either sodium adducts, [ Figure S1 indicates differences in the selectivity and sensitivity of the (+)ESI and (−)ESI modes toward specific BBOA compounds. For example, in PP BBOA ( Figure S1), the (+)ESI TIC is dominated by compounds with low DBE, such as C 8 BrC chromophores have been distinguished by examining time periods of the HPLC/HRMS data corresponding to the PDA absorption peaks extending into the near-UV and visible wavelength ranges.…”

Sources of humic-like substances in the Pearl River Delta, China: positive matrix factorization analysis of PM<sup>2.5</sup> major components and source markers

“…The higher emissions of BVOCs in summer could possibly contribute to the higher HULIS concentrations in this season. In addition to organosulfates, numerous other oxygenated or nitrated organic compound formulas are reported to be HULIS constituents (Lin et al, 2012a), but their formation processes or precursors are much less understood.…”

“…The molecular composition of HULIS was also studied using ultrahigh resolution mass spectrometer (e.g., Wozniak et al, 2008;Lin et al, 2012a, b;Yassine et al, 2012). Through composition study, it was confirmed that biomass burning and secondary formation process were sources of HULIS (Lin et al, 2012a). However, to the best of our knowledge, there is not yet a quantitative source apportionment study of HULIS.…”

Alcohols at the aqueous surface: chain length and isomer effects

“…9 As with most other atmospheric organic compounds, the surface structure of short-chained alcohols in aqueous solution in general is not yet well understood. 10,11 The importance of alcohol functional groups at the liquid-vapor interface is specifically motivated by the newly found extremely low-volatility organic compounds, ELVOCs, which are hypothesized to make a crucial contribution to the "missing secondary organic aerosol" mystery, 12 as well as humic-like substances (HULIS) 13 . Both, ELVOCs and HULIS, are believed to contain significant alcohol functionality.…”