Humic-like Substances (HULIS) in Ship Engine Emissions: Molecular Composition Effected by Fuel Type, Engine Mode, and Wet Scrubber Usage.

Humic-like substances (HULIS), known for their substantial impact on the atmosphere, are identified in marine diesel engine emissions obtained from five different fuels at two engine loads simulating real world scenarios as well as the application of wet sulfur scrubbers. The HULIS chemical composition is characterized by electrospray ionization (ESI) ultrahigh resolution mass spectrometry and shown to contain partially oxidized alkylated polycyclic aromatic compounds as well as partially oxidized aliphatic compounds, both including abundant nitrogen- and sulfur-containing species, and clearly different to HULIS emitted from biomass burning. Fuel properties such as sulfur content and aromaticity as well as the fuel combustion efficiency and engine mode are reflected in the observed HULIS composition. When the marine diesel engine is operated below the optimum engine settings, e.g., during maneuvering in harbors, HULIS-C emission factors are increased (262-893 mg kg-1), and a higher number of HULIS with a shift toward lower degree of oxidation and higher aromaticity is detected. Additionally, more aromatic and aliphatic CHOS compounds in HULIS were detected, especially for high-sulfur fuel combustion. The application of wet sulfur scrubbers decreased the HULIS-C emission factors by 4-49% but also led to the formation of new HULIS compounds. Overall, our results suggest the consideration of marine diesel engines as a relevant regional source of HULIS emissions.

Molecular composition of fresh and aged aerosols from residential wood combustion and gasoline car with modern emission mitigation technology.

Emissions from road traffic and residential heating contribute to urban air pollution. Advances in emission reduction technologies may alter the composition of emissions and affect their fate during atmospheric processing. Here, emissions of a gasoline car and a wood stove, both equipped with modern emission mitigation technology, were photochemically aged in an oxidation flow reactor to the equivalent of one to five days of photochemical aging. Fresh and aged exhausts were analyzed by ultrahigh resolution mass spectrometry. The gasoline car equipped with a three-way catalyst and a gasoline particle filter emitted minor primary fine particulate matter (PM2.5), but aging led to formation of particulate low-volatile, oxygenated and highly nitrogen-containing compounds, formed from volatile organic compounds (VOCs) and gases incl. NOx, SO2, and NH3. Reduction of the particle concentration was also observed for the application of an electrostatic precipitator with residential wood combustion but with no significant effect on the chemical composition of PM2.5. Comparing the effect of short and medium photochemical exposures on PM2.5 of both emission sources indicates a similar trend for formation of new organic compounds with increased carbon oxidation state and nitrogen content. The overall bulk compositions of the studied emission exhausts became more similar by aging, with many newly formed elemental compositions being shared. However, the presence of particulate matter in wood combustion results in differences in the molecular properties of secondary particles, as some compounds were preserved during aging.

Detailed Comparison of Xenon APPI (9.6/8.4 eV), Krypton APPI (10.6/10.0 eV), APCI, and APLI (266 nm) for Gas Chromatography High Resolution Mass Spectrometry of Standards and Complex Mixtures.

Photoionization schemes for mass spectrometry, either by laser or discharge lamps, have been widely examined and deployed. In this work, the ionization characteristics of a xenon discharge lamp (Xe-APPI, 9.6/8.4 eV) have been studied and compared to established ionization schemes, such as atmospheric pressure chemical ionization, atmospheric pressure photoionization with a krypton discharge lamp (Kr-APPI, 10.6/10 eV) and atmospheric pressure laser ionization (266 nm). Addressing the gas-phase ionization behavior has been realized by gas chromatography coupled to high-resolution mass spectrometry without the usage of a dopant. For standard substances, it has been found that Xe-APPI is able to ionize a broad range of polycyclic aromatic hydrocarbons as well as their heteroatom-containing and alkylated derivatives. However, thiol and ester compounds could not be detected. Moreover, Xe-APPI revealed a high tendency to generate oxygenated artifacts, most likely due to a VUV absorption band of oxygen at 148 nm. Beneficially, almost no chemical background, commonly caused by APCI or Kr-APPI due to column blood, plasticizers or impurities, is observed. This advantage is noteworthy for evolved gas analysis without preseparation or for chromatographic coelution. For the complex mixtures, Xe-APPI revealed the predominant generation of radical cations via direct photoionization with a high selectivity toward aromatic core structures with low alkylation. Interestingly, both Xe-APPI and Kr-APPI could sensitively detect sterane cycloalkanes, validated by gas chromatographic retention. The narrowly ionized chemical space could let Xe-APPI find niche applications, e.g., for strongly contaminated samples to reduce the background.