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A key Earth system science question is the role of atmospheric deposition in supplying vital nutrients to the phytoplankton that form the base of marine food webs. Industrial and vehicular pollution, wildfires, volcanoes, biogenic debris, and desert dust all carry nutrients within their plumes throughout the globe. In remote ocean ecosystems, aerosol deposition represents an essential new source of nutrients for primary production. The large spatiotemporal variability in aerosols from myriad sources combined with the differential responses of marine biota to changing fluxes makes it crucially important to understand where, when, and how much nutrients from the atmosphere enter marine ecosystems. This review brings together existing literature, experimental evidence of impacts, and new atmospheric nutrient observations that can be compared with atmospheric and ocean biogeochemistry modeling. We evaluate the contribution and spatiotemporal variability of nutrient-bearing aerosols from desert dust, wildfire, volcanic, and anthropogenic sources, including the organic component, deposition fluxes, and oceanic impacts.

Isoprene (C 5 H 8 ) is the main non-methane hydrocarbon emitted into the global atmosphere. Despite intense research, atmospheric transformations of isoprene leading to secondary organic aerosol (SOA) are still not fully understood, including its multiphase chemical reactions. Herein, we report on the detailed structural characterization of atmospherically relevant isoprene-derived organosulfates (OSs) with a molecular weight (MW) of 212 (C 5 H 8 SO 7 ), which are abundantly present in both ambient fine aerosol (PM 2.5 ) and laboratory-generated isoprene SOA. The results obtained from smog chamber-generated isoprene SOA and aqueous-phase laboratory experiments coupled to the S(IV)-autooxidation chemistry of isoprene, 3-methyl-2(5 H )-furanone, and 4-methyl-2(5 H )-furanone, allowed us for the first time to fully elucidate the isomeric structures of the MW 212 OSs. By applying liquid chromatography interfaced to electrospray ionization high-resolution mass spectrometry, we firmly confirmed six positional isomers of the MW 212 OSs in PM 2.5 collected from different sites in Europe and the United States. Our results also show that despite the low solubility of isoprene in water, aqueous-phase or multiphase chemistry can play an important role in the formation of OSs from isoprene. Possible formation mechanisms for the MW 212 OSs are also tentatively proposed.

From 30 June 2011 to 2 July 2012 PM10 aerosol samples were simultaneously taken every 4th day at four urban background sites in Flanders, Belgium. The sites were in Antwerpen, Gent, Brugge, and Oostende. The PM10 mass concentration was determined by weighing; organic and elemental carbon (OC and EC) were measured by thermal-optical analysis, the wood burning tracers levoglucosan, mannosan and galactosan were determined by gas chromatography/mass spectrometry, 8 water-soluble ions were measured by ion chromatography, and 15 elements were determined by a combination of inductively coupled plasma atomic emission spectrometry and mass spectrometry. The multi-species dataset was subjected to receptor modeling by PMF. The 10 retained factors (with their overall average percentage contributions to the experimental PM10 mass) were wood burning (9.5%), secondary nitrate (24%), secondary sulfate (12.6%), sea salt (10.0%), aged sea salt (19.2%), crustal matter (9.7%), non-ferrous metals (1.81%), traffic (10.3%), non-exhaust traffic (0.52%), and heavy oil burning (3.0%). The average contributions of wood smoke for the four sites were quite substantial in winter and ranged from 12.5 to 20% for the PM10 mass and from 47 to 64% for PM10 OC. Wood burning appeared to be also a notable source of As, Cd, and Pb. The contribution from wood burning to the PM10 mass and OC was also assessed by making use of levoglucosan as single marker compound and the conversion factors of Schmidl et al. (2008), as done in our previous study on wood burning in Flanders (Maenhaut et al., 2012). However, the apportionments were much lower than those deduced from PMF. It seems that the conversion factors of Schmidl et al. (2008) may not be applicable to wood burning in Flanders. From scatter plots of the PMF-derived wood smoke OC and PM versus levoglucosan, we arrived at conversion factors of 9.7 and 22.6, respectively., (Copyright © 2016 Elsevier B.V. All rights reserved.)

In the present work, we have evaluated whether isomeric C5-alkene diols (1,2-dihydroxy-2-methyl-3-butene, 1,2-dihydroxy-3-methyl-3-butene, and 1,4-dihydroxy-2-methyl-2-butene (cis + trans)), which have first been detected upon photooxidation of isoprene in the absence of NO and are known to be formed in the ambient atmosphere, can serve as precursors for the 2-methyltetrols, C5-alkene triols, and 2-methylglyceric acid under low-NO(x) conditions. The C5-alkene diols were prepared following published synthesis procedures. It is shown that under the applied chamber conditions the isomeric C5-alkene diols give rise to 2-methyltetrols with different threo/erythro abundance ratios and that certain diols produce 2-methylglyceric acid, but that they do not form C5-alkene triols. Furthermore, it is shown that the photooxidation of isoprene under the applied chamber conditions employing photolysis of H2O2 under dry conditions yields relatively small amounts of C5-alkene triols compared to those of the 2-methyltetrols, unlike under ambient conditions. It is argued that the chamber conditions are not optimal for the formation of C5-epoxydiols, which serve as gas-phase precursors for the C5-alkene triols, and likely as in some previous studies favor the formation of C5-alkene diols as a result of RO2 + RO2 reactions.

From February 2010 to February 2011 PM10 aerosol samples were simultaneously taken every 4th day at 7 monitoring sites in Flanders, Belgium. Two of the sites (i.e., Borgerhout and Gent) were urban background sites; one (i.e., Mechelen) a suburban background site, and the other four (i.e., Hamme, Lier, Retie, and Houtem) rural background sites, whereby Hamme and Lier were expected to be particularly impacted by biomass burning. The samplings were done for 24h and 47-mm diameter Pallflex® Tissuquartz™ 2500 QAT-UP filters were used. After sampling the PM10 mass concentration was determined by weighing; organic and elemental carbon (OC and EC) were measured by thermal-optical transmission analysis and the wood burning tracers levoglucosan, mannosan, and galactosan were determined by means of gas chromatography/mass spectrometry. The atmospheric concentrations of levoglucosan and the other two monosaccharide anhydrides showed a very clear seasonal variation at each site, with highest levels in winter, followed by autumn, spring, and summer. The levoglucosan levels for 5 of our 7 sites (i.e., Retie, Lier, Mechelen, Borgerhout, and Gent) were very highly correlated with each other (all between site correlation coefficients r>0.9, except for one value of 0.86) and the levels in the parallel samples of these 5 sites were similar, indicating that wood burning at these 5 sites was a regional phenomenon and that it was taking place in many individual houses on similar occasions (e.g., on cold days, weekends or holidays). The levoglucosan levels at Houtem and the correlation coefficients of the 5 sites with Houtem were lower, which is explained by the fact that the latter site is at less than 20 km from the North Sea so that the air there is often diluted by rather clean westerly maritime air. A peculiar behavior was seen for Hamme, with on many occasions very high levoglucosan levels, which was attributed to the fact that there is wood burning going on in several houses nearby this site. From our levoglucosan/mannosan ratios we derived the relative contributions of softwood and hardwood burning, thereby following the same approach as used by Schmidl et al. (Atmos Environ 2008;38:126-41). It was found that softwood burning accounted, on average, for about 70%, and there was little variation in this percentage with site or with season. The levoglucosan data were used to assess the contribution of wood burning to the OC and to the PM10 mass, again following the approach of Schmidl et al. (2008). The annual average contributions of wood burning OC to the PM10 OC were in the range of 20-25% for 6 of our 7 sites and 36% for Hamme; the averages for summer were 2.0-3.9% for the 6 sites and 14.5% for Hamme; the corresponding data for winter were 36-43% and 60%. As to the contribution from wood burning to the PM10 mass, the annual averages were in the range of 4.8-6.3% for 6 of our 7 sites and 13.3% at Hamme; the averages for summer were 0.51-1.14% for the 6 sites and 5.0% for Hamme; the corresponding data for winter were 8.6-11.3% and 22%. Our finding that wood burning is an important contributor to the OC and the PM10 mass, especially in winter, is in line with published data from various other sites in other European countries., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Recent work in our laboratory has shown that the photooxidation of isoprene (2-methyl-1,3-butadiene, C(5)H(8)) leads to the formation of secondary organic aerosol (SOA). In the current study, the chemical composition of SOA from the photooxidation of isoprene over the full range of NO(x) conditions is investigated through a series of controlled laboratory chamber experiments. SOA composition is studied using a wide range of experimental techniques: electrospray ionization-mass spectrometry, matrix-assisted laser desorption ionization-mass spectrometry, high-resolution mass spectrometry, online aerosol mass spectrometry, gas chromatography/mass spectrometry, and an iodometric-spectroscopic method. Oligomerization was observed to be an important SOA formation pathway in all cases; however, the nature of the oligomers depends strongly on the NO(x) level, with acidic products formed under high-NO(x) conditions only. We present, to our knowledge, the first evidence of particle-phase esterification reactions in SOA, where the further oxidation of the isoprene oxidation product methacrolein under high-NO(x) conditions produces polyesters involving 2-methylglyceric acid as a key monomeric unit. These oligomers comprise approximately 22-34% of the high-NO(x) SOA mass. Under low-NO(x) conditions, organic peroxides contribute significantly to the low-NO(x) SOA mass (approximately 61% when SOA forms by nucleation and approximately 25-30% in the presence of seed particles). The contribution of organic peroxides in the SOA decreases with time, indicating photochemical aging. Hemiacetal dimers are found to form from C(5) alkene triols and 2-methyltetrols under low-NO(x) conditions; these compounds are also found in aerosol collected from the Amazonian rainforest, demonstrating the atmospheric relevance of these low-NO(x) chamber experiments.