Marine aerosol samples were collected over the western North Pacific along the latitudinal transect from 44° N to 10° N in late summer 2008 for measurements of organic nitrogen (ON) and organic carbon (OC) as well as isotopic ratios of total nitrogen (TN) and total carbon (TC). Increased concentrations of methanesulfonic acid (MSA) and diethylammonium (DEA⁺) at 40–44° N and subtropical regions (10–20° N) together with averaged satellite chlorophyll-a data and 5-day back trajectories suggest a significant influence of marine biological activities on aerosols in these regions. ON exhibited increased concentrations up to 260 ngN m⁻³ in these marine biologically influenced aerosols. Water-insoluble organic nitrogen (WION) was found to be the most abundant nitrogen in the aerosols, accounting for 55 ± 16% of total aerosol nitrogen. In particular, the average WION/ON ratio was as high as 0.93 ± 0.07 at 40–44° N. These results suggest that marine biological sources significantly contributed to ON, a majority of which is composed of water-insoluble fractions in the study region. Analysis of the stable carbon isotopic ratios (δ¹³C) indicated that, on average, marine-derived carbon accounted for ~88 ± 12% of total carbon in the aerosols. In addition, the δ¹³C showed higher values (from −22 to −20‰) when ON/OC ratios increased from 0.15 to 0.35 in marine biologically influenced aerosols. These results clearly show that organic nitrogen is enriched in organic aerosols originated from an oceanic region with high biological productivity, indicating a preferential transfer of nitrogen-containing organic compounds from the sea surface to the marine atmosphere. Both WION concentrations and WION/water-insoluble organic carbon (WIOC) ratios tended to increase with increasing local wind speeds, indicating that sea-to-air emissions of ON via sea spray contribute significantly to the marine organic aerosols over the study region.

Day‐ and nighttime aerosol samples were collected at an urban site in New Delhi, India, in winter 2006–2007. They were studied for low molecular weight dicarboxylic acids and related compounds, as well as total water‐soluble organic carbon (TWSOC). High concentrations of diacids (up to 6.03 μg m⁻³), TWSOC, and OC were obtained, which are substantially higher than those previously observed at other urban sites in Asia. Daytime TWSOC/OC ratio (37%) was on average higher than that in nighttime (25%). In particular, more water‐soluble OC (M‐WSOC) to TWSOC ratio in daytime (50%) was twice higher than in nighttime (27%), suggesting that aerosols in New Delhi are photochemically more processed in daytime to result in more water‐soluble organic compounds. Oxalic acid (C₂) was found as the most abundant dicarboxylic acid, followed by succinic (C₄) and malonic (C₃) acids. Contributions of C₂ to M‐WSOC were greater (av. 8%) in nighttime than daytime (av. 3%). Positive correlations of C₂ with malic acid (hC₄), glyoxylic acid (ωC₂), and relative humidity suggest that secondary production of C₂ probably in aqueous phase is important in nighttime via the oxidation of both longer‐chain diacids and ωC₂. C₂ also showed a positive correlation with potassium (K⁺) in nighttime, suggesting that the enhanced C₂ concentrations are associated with biomass/biofuel burning. More tight, positive correlation between less water‐soluble OC (L‐WSOC) and K⁺ was found in both day‐ and nighttime, suggesting that L‐WSOC, characterized by longer chain and/or higher molecular weight compounds, is significantly influenced by primary emissions from biomass/biofuel burning.

To investigate the seasonal changes in biogenic water-soluble organic carbon (WSOC) aerosols in a boreal forest, aerosol samples were collected continuously in the canopy of a deciduous forest in northern Japan during 2009–2010. Stable carbon isotopic composition of WSOC (δ¹³C_WSOC) in total suspended particulate matter (TSP) exhibited a distinct seasonal cycle, with lower values from June through September (−25.5±0.5 ‰). This cycle follows the net CO₂ exchange between the forest ecosystem and the atmosphere, indicating that δ¹³C_WSOC likely reflects the biological activity at the forest site. WSOC concentrations showed the highest values in early summer and autumn. Positive matrix factorization (PMF) analysis indicated that the factor in which biogenic secondary organic aerosols (BSOAs) dominated accounted for ~40 % of the highest concentrations of WSOC, where BSOAs mostly consisted of α-/β-pinene SOA. In addition, primary biological aerosol particles (PBAPs) made similar contributions (~57 %) to the WSOC near the forest floor in early summer. This finding indicates that the production of both primary and secondary WSOC aerosols is important during the growing season in a deciduous forest. The methanesulfonic acid (MSA) maximum was also found in early summer and had a distinct vertical gradient with larger concentrations near the forest floor. Together with the similar vertical gradients found for WSOC and δ¹³C_WSOC as well as the α-/β-pinene SOA tracers, our results indicate that the forest floor, including ground vegetation and soil, acts as a significant source of WSOC in TSP within a forest canopy at the study site.

We designed a continuous soot monitoring system (COSMOS) for fully automated, high-sensitivity, continuous measurement of light absorption by black carbon (BC) aerosols. The instrument monitors changes in transmittance across an automatically advancing quartz fiber filter tape using an LED at a 565 nm wavelength. To achieve measurements with high sensitivity and a lower detectable light absorption coefficient, COSMOS uses a double-convex lens and optical bundle pipes to maintain high light intensity and signal data are obtained at 1000 Hz. In addition, sampling flow rate and optical unit temperature are actively controlled. The inlet line for COSMOS is heated to 400 °C to effectively volatilize non-refractory aerosol components that are internally mixed with BC. In its current form, COSMOS provides BC light absorption measurements with a detection limit of 0.45 Mm⁻¹ (0.045 µg m⁻³ for soot) for 10 min. The unit-to-unit variability is estimated to be within ±1%, demonstrating its high reproducibility. The absorption coefficients determined by COSMOS agreed with those by a particle soot absorption photometer (PSAP) to within 1% (r² = 0.97). The precision (±0.60 Mm⁻¹) for 10 min integrated data was better than that of PSAP and an aethalometer under our operating conditions. These results showed that COSMOS achieved both an improved detection limit and higher precision for the filter-based light absorption measurements of BC compared to the existing methods.

It is critical to understand how variations in chemical composition in surface seawater (SSW) affect the chemistry of marine atmospheric aerosols. We investigated the sea-to-air transfer of dissolved organic carbon (DOC) via cruise measurements of both ambient aerosols and SSW in the Oyashio and its coastal regions, the western subarctic Pacific during early spring. Sea spray aerosols (SSAs) were selected based on the stable carbon isotope ratio of water-soluble organic carbon (WSOC) (δ¹³C_WSOC) and concentrations of glucose as a molecular tracer in marine aerosols together with local surface wind speed data. For both SSA and SSW samples, excitation-emission matrices were obtained to examine the transfer of fluorescent organic material. We found that the ratios of fluorescence intensity of humic-like and protein-like substances in the submicrometer SSAs were significantly larger than those in the bulk SSW (~63%). This ratio was also larger for the supermicrometer SSAs than for the SSW. The results suggest significant decomposition of protein-like DOC on a timescale of <12–24 h and/or preferential production of humic-like substances in the atmospheric aerosols regardless of the particle size. This study provides unique insights into the complex transfer of DOC from the ocean surface to the atmosphere.