Abstract. Particulate amines play an important role for the particle acidity and 43 hygroscopicity and also contribute to secondary organic aerosol mass. We investigated 44 the sources and mixing states of particulate amines using a single-particle aerosol 45 mass spectrometer (SPAMS) during summer and winter 2014 at a rural site in the 46 Pearl River Delta, China. Amine-containing particles accounted for 12.8 % and 9.2 % 47 of the total detected individual particles in summer and winter, respectively. only 6.7 % of the total amine-containing particles were found to be mixed with 57 ammonium, while in winter this percentage increased to 55 %. The ammonium-poor 58 state of amine-containing particles in summer may have been caused by the 59 displacement of particle-phase ammonium by amine uptake, which was more efficient 60 in summer at higher ambient RH (72 ± 13 %) than in winter (63 ± 11 %). In 61 ECOC-type amine-containing particles, the time series of the amine peak area and the 62 sum of the nitrate and sulfate peak areas were similar in both summer and winter, 63 suggesting the formation of aminium sulfate and nitrate salts. The particle acidity of 64 ECOC-type amine-containing particles was represented by the relative acidity ratio 65 (R a ), which was defined as the ratio of the total sulfate and nitrate peak areas to the 66 ammonium peak area. The R a decreased from 348 ± 335 and 28 ± 14 to 10 ± 5 and 9 ± 67 2 in summer and winter, respectively, after including amines along with the 68 ammonium in the acidity calculation, suggesting that it is reasonable to consider 69 amines when estimating particle acidity.

<p><strong>Abstract.</strong> Black carbon (BC) is an important climate forcer in the atmosphere. Amplification of light absorption can occur by coatings on BC aerosols, an effect that remains one of the major sources of uncertainties for accessing the radiative forcing of BC. In this study, the absorption enhancement factor (E<sub>abs</sub>) was quantified by the minimum R squared (MRS) method using elemental carbon (EC) as the tracer. Two field campaigns were conducted in urban Guangzhou at the Jinan university super site during both wet season (July 31–September 10, 2017) and dry season (November 15, 2017–January 15, 2018) to explore the temporal dynamics of BC optical properties. The average concentration of EC was 1.94 ± 0.93 and 2.81 ± 2.01 μgC m<sup>−3</sup> in the wet and dry seasons, respectively. Mass absorption efficiency at 520 nm by primary aerosols (MAE<sub>p520</sub>) determined by MRS exhibit a strong seasonality (8.6 m<sup>2</sup>g<sup>−1</sup> in the wet season and 16.8 m<sup>2</sup>g<sup>−1</sup> in the dry season). E<sub>abs520</sub> was higher in the wet season (1.51 ± 0.50) and lower in the dry season (1.29 ± 0.28). Absorption Ångström exponent (AAE<sub>470-660</sub>) in the dry season (1.46 ± 0.12) were higher than that in the wet season (1.37 ± 0.10). Collective evidence showed that the active biomass burning (BB) in dry season effectively altered optical properties of BC, leading to elevated MAE, MAE<sub>p</sub> and AAE in dry season comparing to those in wet season. Diurnal E<sub>abs520</sub> was positively correlated with AAE<sub>470-660</sub> (<i>R</i><sup>2</sup> = 0.71) and negatively correlated with the AE33 aerosol loading compensation parameter (<i>k</i>) (<i>R</i><sup>2</sup> = 0.74) in the wet season, but these correlations were significantly weaker in the dry season, which may be related to the impact of BB. This result suggests that lensing effect was dominating the AAE diurnal variability during the wet season. The effect of secondary processing on Eabs diurnal dynamic were also investigated. The E<sub>abs520</sub> exhibit a clear dependency on secondary organic carbon to organic carbon ratio (SOC/OC). E<sub>abs520</sub> correlated well with nitrate, implying that gas-particle partitioning of semi-volatile compounds may potentially play an important role in steering the diurnal fluctuation of E<sub>abs520</sub>. In dry season, the diurnal variability of E<sub>abs520</sub> was associated with photochemical aging as evidenced by the good correlation (<i>R</i><sup>2</sup> = 0.69) between oxidant concentrations (O<sub>x</sub>=O<sub>3</sub>+NO<sub>2</sub>) and E<sub>abs520</sub>.</p>

Highlights 19 Nitrogen-containing organics (NOCs) were highly internally mixed with photochemically 20 produced secondary oxidized organics 21  More than 50% of NOCs were well predicted by secondary formation from these 22 oxidized organics and ammonium 23  Higher relative humidity and particle acidity facilitated the formation of NOCs 24 2 Abstract 25Nitrogen-containing organic compounds (NOCs) substantially contribute to light 26 absorbing organic aerosols, although the atmospheric processes responsible for the secondary 27 formation of these compounds are poorly understood. In this study, seasonal atmospheric 28 processing of NOCs were investigated by single particle mass spectrometry in urban 29Guangzhou from 2013-2014. The relative abundance of NOCs was found to be strongly 30 enhanced by internal mixing with the photochemically produced secondary oxidized organics 31 (such as formate, acetate, pyruvate, methylglyoxal, glyoxylate, oxalate, malonate and 32 succinate). Furthermore, the co-occurrence of NOCs with ammonium was also observed. 33Interestingly, the relative abundance of NOCs was inversely correlated with ammonium, while 34 their number fractions were positively correlated. Multiple linear regression analysis and 35 positive matrix factorization analysis were performed to predict the relative abundance of NOCs 36 generated from oxidized organics and ammonium. Both results showed close associations (R 2 > 37 0.7, p < 0.01) between the predicted NOCs and the observed values. Increased humidity and 38 higher particle acidity were found to promote the production of NOCs. Higher relative 39 contributions of NOCs were observed in summer and autumn, in comparison to spring and 40 winter, due to the relatively higher contribution of oxidized organics and NH3/NH + 4 in summer 41 and autumn periods. To the best of our knowledge, this is the first direct field observation study 42 establishing a close association between NOCs and both oxidized organics and ammonium. 43These findings have substantial implications on the role of ammonium in the atmosphere, 44 particularly in models predicting the evolution and deposition of NOCs. 45 3 https://doi.

Abstract. 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.

Abstract. The composition, morphology, and mixing structure of individual cloud residues (RES) and interstitial particles (INT) at a mountain-top site were investigated. Eight types of particles were identified, including sulfate-rich (S-rich), S-organic matter (OM), aged soot, aged mineral, aged fly ash, aged metal, fresh mixture, and aged mixture. A shift of dominant particle types from S-rich (29 %) and aged soot (27 %) in the INT to S-OM (24 %) and aged mixture (22 %) in the RES is observed. In particular, particles with organic shells are enriched in the RES (30 %) relative to the INT (12 %). Our results highlight the in-cloud formation of more oxidized organic shells on the activated particles. We also show that in-cloud processes may result in less compact soot, with the fractal dimensions (Df) of soot in the RES (1.82 ± 0.12) lower than those in the INT (2.11 ± 0.09). This research emphasizes the role of in-cloud processes on the chemistry and microphysical properties of individual particles. Given that organic coatings may determine the particle hygroscopicity, activation ability, and heterogeneous chemical reactivity, the increase of OM-shelled particles upon in-cloud processes should have considerable implications.