Water-soluble organic compounds (WSOC) and methanol-soluble organic compounds (MSOC) in smoke particles emitted from residential coal combustion were characterized by ultrahigh-resolution mass spectrometry. The results showed that the molecular compositions of WSOC and MSOC are different. S-containing compounds (CHOS and CHONS) are found to be the dominant components (65–87%) of the WSOC, whereas CHO and CHON compounds make a great contribution (79–96%) to the MSOC samples. It is worth noting that greater abundance of S-containing compounds was found in smoke produced from coal combustion compared to biomass burning and atmospheric samples. The molecular compositions of WSOC and MSOC also varied significantly depending on the maturity of the coal. The WSOC and MSOC derived from the combustion of low-maturity coal contained a higher proportion of oxidized functional groups but with a lower degree of aromaticity than the compounds derived from the combustion of high-maturity coal. Our findings suggest that organic molecules with a high modified aromaticity index, low O/C ratio, and low polarity showed stronger light absorption. This study also suggests that CHO and CHON compounds significantly contributed to the light absorption of WSOC and MSOC and that the contribution of CHON may be stronger.

No abstract

The dynamic behavior of infrared (IR)-observable species during the methylene blue [i.e., MB, (CH 3 ) 2 N(C 6 H 3 )NS + (C 6 H 3 )N(CH 3 ) 2 Cl -] photocatalytic degradation (PCD) on TiO 2 has been investigated at 30°C. Exposure of MB/TiO 2 to UV illumination led to the scission of the N-CH 3 bond followed by breaking of the C-H and CdN bonds in the MB central aromatic ring and the side aromatic rings, indicating demethylation as the first step of the MB PCD. The bond breaking in the MB molecule and subsequent reactions produced charge-containing intermediates (i.e., carboxylate (RCOO -) and R-NH 3 + ), slowing down the conversion of MB to CO 2 , H 2 O, NH 4 + , and SO 4 2-. Probing the MB PCD by adsorbed ethanol revealed that the demethylation step was initiated by the OH/OD radical (‚OH/‚OD) and the breaking of CdN and CdS-C in the MB central aromatic ring by H + /electron transfer. In situ IR coupled with the use of ethanol as a probe molecule provides an excellent method for investigating the PCD mechanism.

N-containing organic compounds (NOCs) in humic-like substances (HULIS) emitted from biomass burning (BB) and coal combustion (CC) were characterized by ultrahigh-resolution mass spectrometry in the positive electrospray ionization mode. Our results indicate that NOCs include CHON+ and CHN+ groups, which are detected as a substantial fraction in both BB- and CC-derived HULIS, and suggest that not only BB but also CC is the potential important source of NOCs in the atmosphere. The CHON+ compounds mainly consist of reduced nitrogen compounds with other oxygenated functional groups, and straw- and coal-smoke HULIS exhibit a lower degree of oxidation than pine-smoke HULIS. In addition, the NOCs with higher N atoms (N2 and/or N3) generally bear higher modified aromaticity index (AImod) values and are mainly contained in BB HULIS, especially in straw-smoke HULIS, whereas the NOCs with a lower N atom (N1) always have relatively lower AImod values and are the dominant NOCs in CC HULIS. These findings imply that the primary emission from CC may be a significant source of N1 compounds, whereas high N number (e.g., N2–3) compounds could be associated with burning of biomass materials. Further study is warranted to distinguish the NOCs from more sources.

No abstract

No abstract

This study investigated the degradation of sulfadiazine in three soils and also determined its sorption and hydrolysis behaviors as well. At the spike concentration of 10 mg/kg, the half-lives for sulfadiazine in the aerobic nonsterile soils ranged from 12 days to 18 days. Sulfadiazine was more persistent in the anoxic soils with the half-lives ranging between 57 days and 237 days and soil microorganisms played little role in the dissipation process under anoxic conditions. The decline in sulfadiazine concentrations was also observed in the sterile soils under aerobic conditions. Hydrolysis could not explain this phenomena as hydrolysis of sulfadiazine was pH dependent. Sulfadiazine only hydrolyzed to a very limited degree at acidic pH. Increased sorption was observed for sulfadiazine in soil 1 (pH 4.3) when the contact time increased to 14 days, but no significant increase in sorption was found for soil 2 (pH 7.2) and soil 3 (pH 8.5).

No abstract