Detection of ship plumes from residual fuel operation in emission control areas using single-particle mass spectrometry

Ships are among the main contributors to global air pollution, with substantial impacts on climate and public health. To improve air quality in densely populated coastal areas and to protect sensitive ecosystems, sulfur emission control areas (SECAs) were established in many regions of the world. Ships in SECAs operate with low-sulfur fuels, typically distillate fractions such as marine gas oil (MGO). Alternatively, exhaust gas-cleaning devices (“scrubbers”) can be implemented to remove SO2 from the exhaust, thus allowing the use of cheap high-sulfur residual fuels. Compliance monitoring is established in harbors but is difficult in open water because of high costs and technical limitations. Here we present the first experiments to detect individual ship plumes from distances of several kilometers by single-particle mass spectrometry (SPMS). In contrast to most monitoring approaches that evaluate the gaseous emissions, such as manned or unmanned surveillance flights, sniffer technologies and remote sensing, we analyze the metal content of individual particles which is conserved during atmospheric transport. We optimized SPMS technology for the evaluation of residual fuel emissions and demonstrate their detection in a SECA. Our experiments show that ships with installed scrubbers can emit PM emissions with health-relevant metals in quantities high enough to be detected from more than 10 km distance, emphasizing the importance of novel exhaust-cleaning technologies and cleaner fuels. Because of the unique and stable signatures, the method is not affected by urban background. With this study, we establish a route towards a novel monitoring protocol for ship emissions. Therefore, we present and discuss mass spectral signatures that indicate the particle age and thus the distance to the source. By matching ship transponder data, measured wind data and air mass back trajectories, we show how real-time SPMS data can be evaluated to assign distant ship passages.

Detection of Ship Plumes from Residual Fuel Operation in Emission Control Areas using Single-Particle Mass Spectrometry

Ships are main contributors to global air pollution with substantial impacts on climate and public health. To improve air quality in densely populated coastal areas and to protect sensitive ecosystems, sulfur emission control areas (SECA) were established in many regions of the world. Ships in SECAs operate with low-sulfur fuels, typically distillate fractions such as marine gas oil (MGO). Alternatively, exhaust gas cleaning devices (scrubbers) can be implemented to remove SO2 from the exhaust, thus allowing the use of cheap high-sulfur residual fuels. Compliance monitoring is established in harbors, but difficult in open water because of high costs and technical limitations. Here we present the first experiments to detect individual ship plumes from distances of several kilometers by single-particle mass spectrometry (SPMS). In contrast to most monitoring approaches that evaluate the gaseous emissions, such as manned or unmanned surveillance flights, sniffer technologies and remote sensing, we analyze the chemical composition of the particulate phase that is transported by the wind over long distances. We optimized SPMS technology for the evaluation of residual fuel emissions and demonstrate their detection in a SECA. Our experiments show that ships with installed scrubbers can emit PM emissions with health-relevant metals in quantities high enough to be detected from more than 10 km distance, emphasizing the importance of novel exhaust cleaning technologies and cleaner fuels. Because of the unique and stable metal signatures, our method is not affected by urban background. With this study, we establish a route towards a novel monitoring protocol for ship emissions. Therefore, we present and discuss mass spectral signatures that indicate the particle age, and thus the distance to the source. By matching ship transponder data, measured wind data and air mass back trajectories, we show, how real-time SPMS data can be evaluated to assign distant ship passages.

Resonance-enhanced detection of metals in aerosols using single-particle mass spectrometry

We describe resonance effects in laser desorption–ionization (LDI) of particles that substantially increase the sensitivity and selectivity to metals in single-particle mass spectrometry (SPMS). Within the proposed scenario, resonant light absorption by ablated metal atoms increases their ionization rate within a single laser pulse. By choosing the appropriate laser wavelength, the key micronutrients Fe, Zn and Mn can be detected on individual aerosol particles with considerably improved efficiency. These ionization enhancements for metals apply to natural dust and anthropogenic aerosols, both important sources of bioavailable metals to marine environments. Transferring the results into applications, we show that the spectrum of our KrF-excimer laser is in resonance with a major absorption line of iron atoms. To estimate the impact of resonant LDI on the metal detection efficiency in SPMS applications, we performed a field experiment on ambient air with two alternately firing excimer lasers of different wavelengths. Herein, resonant LDI with the KrF-excimer laser (248.3 nm) revealed iron signatures for many more particles of the same aerosol ensemble compared to the more common ArF-excimer laser line of 193.3 nm (nonresonant LDI of iron). Many of the particles that showed iron contents upon resonant LDI were mixtures of sea salt and organic carbon. For nonresonant ionization, iron was exclusively detected in particles with a soot contribution. This suggests that resonant LDI allows a more universal and secure metal detection in SPMS. Moreover, our field study indicates relevant atmospheric iron transport by mixed organic particles, a pathway that might be underestimated in SPMS measurements based on nonresonant LDI. Our findings show a way to improve the detection and source attribution capabilities of SPMS for particle-bound metals, a health-relevant aerosol component and an important source of micronutrients to the surface oceans affecting marine primary productivity.

High secondary formation of nitrogen-containing organics (NOCs) and its possible link to oxidized organics and ammonium

Nitrogen-containing organic compounds (NOCs) substantially contribute to light-absorbing organic aerosols, although the atmospheric processes responsible for the secondary formation of these compounds are poorly understood. In this study, seasonal atmospheric processing of NOCs is investigated using single-particle mass spectrometry in urban Guangzhou from 2013 to 2014. The relative abundance of NOCs is found to be strongly enhanced when they are internally mixed with photochemically produced secondary oxidized organics (i.e., formate, acetate, pyruvate, methylglyoxal, glyoxylate, oxalate, malonate, and succinate) and ammonium (NH4+). Moreover, both the hourly detected particle number and the relative abundance of NOCs are highly correlated with those of secondary oxidized organics and NH4+. Therefore, it is hypothesized that the secondary formation of NOCs is most likely linked to oxidized organics and NH4+. Results from both multiple linear regression analysis and positive matrix factorization analysis further show that the relative abundance of NOCs could be well predicted (R2 > 0.7, p < 0.01) by oxidized organics and NH4+. Interestingly, the relative abundance of NOCs is inversely correlated with NH4+, whereas their number fractions are positively correlated. This result suggests that although the formation of NOCs does require the involvement of NH3/NH4+, the relative amount of NH4+ may have a negative effect. Higher humidity and NOx likely facilitates the conversion of oxidized organics to NOCs. Due to the relatively high oxidized organics and NH3/NH4+, the relative contributions of NOCs in summer and fall were higher than those in spring and winter. To the best of our knowledge, this is the first direct field observation study reporting a close association between NOCs and both oxidized organics and NH4+. These findings have substantial implications for the role of NH4+ in the atmosphere, particularly in models that predict the evolution and deposition of NOCs.Highlights. NOCs were highly internally mixed with photochemically produced secondary oxidized organics NOCs could be well predicted by the variations of these oxidized organics and NH4+ Higher relative humidity and NOx may facilitate the conversion of these oxidized organics to NOCs