Surfactants account for minor fractions of total organic carbon in the ocean but can significantly influence the production of primary marine aerosol particles (PMA) at the sea surface via modulation ...of bubble surface tension. During September and October 2016, model PMA (mPMA) were produced from seawater by bursting bubbles at two biologically productive and two oligotrophic stations in the western North Atlantic Ocean. Total concentrations of surfactants extracted from mPMA and seawater were quantified and characterized via measurements of surface tension isotherms and critical micelle concentrations (CMCs). Surfactant CMCs in biologically productive seawater were lower than those in the oligotrophic seawater suggesting that surfactant mixtures in the two regions were chemically distinct. mPMA surfactants were enriched in all regions relative to those in the associated seawater. Surface tension isotherms indicate that mPMA surfactants were weaker than corresponding seawater surfactants. mPMA from biologically productive seawater contained higher concentrations of surfactants than those produced from oligotrophic seawater, supporting the hypothesis that seawater surfactant properties modulate mPMA surfactant concentrations. Diel variability in concentrations of seawater and mPMA surfactants in some regions is consistent with biological and/or photochemical processing. This work demonstrates direct links between surfactants in mPMA and those in the associated seawater.
Breaking waves on the ocean surface produce bubbles that, upon bursting, inject seawater constituents into the atmosphere. Nascent aerosols were generated by bubbling zero‐air through flowing ...seawater within an RH‐controlled chamber deployed at Bermuda and analyzed for major chemical and physical characteristics. The composition of feed seawater was representative of the surrounding ocean. Relative size distributions of inorganic aerosol constituents were similar to those in ambient air. Ca2+ was significantly enriched relative to seawater (median factor = 1.2). If in the form of CaCO3, these enrichments would have important implications for pH‐dependent processes. Other inorganic constituents were present at ratios indistinguishable from those in seawater. Soluble organic carbon (OC) was highly enriched in all size fractions (median factor for all samples = 387). Number size distributions exhibited two lognormal modes. The number production flux of each mode was linearly correlated with bubble rate. At 80% RH, the larger mode exhibited a volume centroid of ∼5‐μm diameter and included ∼95% of the inorganic sea‐salt mass; water comprised 79% to 90% of volume. At 80% RH, the smaller mode exhibited a number centroid of 0.13‐μm diameter; water comprised 87% to 90% of volume. The median mass ratio of organic matter to sea salt in the smallest size fraction (geometric mean diameter = 0.13 μm) was 4:1. These results support the hypothesis that bursting bubbles are an important global source of CN and CCN with climatic implications. Primary marine aerosols also influence radiative transfer via multiphase processing of sulfur and other climate‐relevant species.
The oceans hold a massive quantity of organic carbon, nearly all of which is dissolved and more than 95% is refractory, cycling through the oceans several times before complete removal. The vast ...reservoir of refractory dissolved organic carbon (RDOC) is a critical component of the global carbon cycle that is relevant to our understanding of fundamental marine biogeochemical processes and the role of the oceans in climate change with respect to long‐term storage and sequestration of atmospheric carbon dioxide. Here we show that RDOC includes surface‐active organic matter that can be incorporated into primary marine aerosol produced by bursting bubbles at the sea surface. We propose that this process will deliver RDOC from the sea surface to the atmosphere wherein its photochemical oxidation corresponds to a potentially important and hitherto unknown removal mechanism for marine RDOC.
Key Points
Dissolved organic carbon in the deep ocean contains organic surfactants
Primary marine aerosol can be enriched in refractory dissolved organic carbon
Atmospheric removal pathway for marine refractory dissolved organic carbon
During summer 2002, soluble trace gases, the ionic composition of size‐resolved aerosols, and meteorological conditions were measured from the National Oceanic and Atmospheric Administration ship ...Ronald H. Brown in coastal air along the eastern U.S. seaboard. Aerosol acidities were extrapolated from direct pH measurements in minimally diluted extracts and were also inferred from the measured phase partitioning and thermodynamic properties of HCl, HNO3, NH3, HCOOH, and CH3COOH. Median pHs for 0.75‐ through 25‐μm geometric mean diameter (GMD) size fractions based on direct measurements (2.6–3.9) were higher than those inferred from HCl partitioning (1.7–3.3). Phase disequilibria caused negative deviations in median pHs inferred from HNO3 partitioning with aerosol size fractions greater than 2.8‐μm GMD; pHs inferred for smaller size fractions (median values of 1.9–3.0) were similar to those based on HCl (median values of 1.5–3.0). The pHs inferred from NH3 partitioning were significantly lower than those estimated by other approaches; causes for this apparent bias are not known. The dominance of gas‐phase HCOOH and CH3COOH was generally consistent with predicted phase partitioning with acidic aerosols. Typically large diel excursions in most gases implied corresponding variability in aerosol acidity. The pHs inferred from maximum and minimum mixing ratios of gases over each aerosol sampling interval suggested median 12‐hour variations of ∼0.4–0.7 pH unit. Total acidity (Ht = H+ + undissociated acids) was greater than H+ by 1–2 orders of magnitude in all size fractions; most Ht was in the form of HSO4−.
Precipitation composition was characterized at 14 remote sites between 65 degree N and 51 degree S. Anthropogenic sources contributed to non-sea-salt (nss) SO sub(4) super(2-), NO sub(3) super(-), ...and NH sub(4) super(+) in North Atlantic precipitation. Biogenic sources accounted for 0.4-3.3 mu eq L super(-1) of volume-weighted-average (VWA) nss SO sub(4) super(2-) in marine precipitation. SO sub(4) super(2-) at the continental sites (2.9-7.7 mu eq L super(-1)) was generally higher. VWA NO sub(3) super(-) (0.5-1.3 mu eq L super(-1)) and NH sub(4) super(+) (0.5-2.6 mu eq L super(-1)) at marine-influenced, Southern Hemispheric sites were generally less than those at continental sites (1.4-4.8 mu eq L super(-1) and 2.3-4.2 mu eq L super(-1), respectively). VWA pH ranged from 4.69 to 5.25. Excluding the North Atlantic, nss SO sub(4) super(2-), NO sub(3) super(-), and NH sub(4) super(+) wet depositions were factors of 4-47, 5-61, and 3-39, respectively, less than those in the eastern United States during 2002-04. HCOOH sub(t) (HCOOH sub(aq) + HCOO super(-)) and CH sub(3)COOH sub(t) (CH sub(3)COOH sub(aq) + CH sub(3)COO super(-)) concentrations and depositions at marine sites overlapped, implying spatially similar source strengths from marine-derived precursors. Greater variability at continental sites suggests heterogeneity in terrestrial source strengths. Seasonality in deposition was driven by variability in precipitation amount, wind velocity, transport, and emissions. Between 1980 and 2009, nss SO sub(4) super(2-) at Bermuda decreased by 85% in response to decreasing U.S. SO sub(2) emissions; trends in NO sub(3) super(-) and NH sub(4) super(+) were inconsequential. Corresponding decreases in acidity, as reflected in the significant 30% decline in VWA H super(+), impacted pH-dependent chemical processes. Comparisons between measurements and models indicate that current predictive capabilities are uncertain by factors of 2 or more.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A negative‐ion proton‐transfer chemical ionization mass spectrometer was deployed on a mobile tower‐mounted platform during Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT) to ...measure nitrous acid (HONO) in the winter of 2011. High resolution vertical profiles revealed (i) HONO gradients in nocturnal boundary layers, (ii) ground surface dominates HONO production by heterogeneous uptake of NO2, (iii) significant quantities of HONO may be deposited to the ground surface at night, (iv) daytime gradients indicative of ground HONO production or emission, and (v) an estimated surface HONO reservoir comparable or larger than integrated daytime HONO surface production. Nocturnal integrated column observations of HONO and NO2 allowed direct evaluation of nocturnal ground surface uptake coefficients for these species (γNO2, surf = 2 × 10−6 to 1.6 × 10−5 and γHONO, surf = 2 × 10−5 to 2 × 10−4). A chemical model showed that the unknown source of HONO was highest in the morning, 4 × 106 molecules cm−3 s−1 (600 pptv h−1), declined throughout the day, and minimized near 1 × 106 molecules cm−3 s−1 (165 pptv h−1). The quantity of surface‐deposited HONO was also modeled, showing that HONO deposited to the surface at night was at least 25%, and likely in excess of 100%, of the calculated unknown daytime HONO source. These results suggest that if nocturnally deposited HONO forms a conservative surface reservoir, which can be released the following day, a significant fraction of the daytime HONO source can be explained for the NACHTT observations.
Key Points
HONO vertical gradients form on nights with stable nocturnal boundary layers
Nocturnal HONO production consistent with ground surface area dominance
Surface deposition of HONO may be a reservoir for the unknown daytime source
Characteristic vegetation and biofuels in major ecosystems of southern Africa were sampled during summer and autumn 2000 and burned under semicontrolled conditions. Elemental compositions of fuels ...and ash and emissions of CO2, CO, CH3COOH, HCOOH, NOX, NH3, HONO, HNO3, HCl, total volatile inorganic Cl and Br, SO2 and particulate C, N, and major ions were measured. Modified combustion efficiencies (MCEs, median = 0.94) were similar to those of ambient fires. Elemental emissions factors (EFel) for CH3COOH were inversely correlated with MCEs; EFels for heading and mixed grass fires were higher than those for backing fires of comparable MCEs. NOX, NH3, HONO, and particulate N accounted for a median of 22% of emitted N; HNO3 emissions were insignificant. Grass fires with the highest EFels for NH3 corresponded to MCEs in the range of 0.93; grass fires with higher and low MCEs exhibited lower EFels. NH3 emissions for most fuels were poorly correlated with fuel N. Most Cl and Br in fuel was emitted during combustion (median for each = 73%). Inorganic gases and particulate ions accounted for medians of 53% and 30% of emitted Cl and Br, respectively. About half of volatile inorganic Cl was HCl indicating significant emissions of other gaseous inorganic Cl species. Most fuel S (median = 76%) was emitted during combustion; SO2 and particulate SO42− accounted for about half the flux. Mobilization of P by fire (median emission = 82%) implies large nutrient losses from burned regions and potentially important exogenous sources of fertilization for downwind ecosystems.
During summer 2004, a comprehensive suite of reactive trace gases (including halogen radicals and precursors, ozone, reactive N, soluble acids, and hydrocarbons), the chemical and physical ...characteristics of size‐resolved aerosols, actinic flux, and related physical conditions were measured at Appledore Island, Maine, as part of the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT). Sea‐salt mass averaged 4 to 8 times lower than that over the open North Atlantic Ocean. Production in association with sea salt was the primary source for inorganic Cl and Br. Acid displacement of sea‐salt Cl− primarily by HNO3 sustained high HCl mixing ratios (often >2000 pptv) during daytime. Median pHs for the larger sea‐salt size fractions (geometric mean diameters, GMDs ≥ 2.9 μm) ranged from 3.1 to 3.4; median pHs for sub‐μm size fractions were ≤ 1.6. Cl* (including HOCl and Cl2) ranged from <20 to 421 pptv Cl but was less than the detection limit (DL) during most sampling intervals. Periods during which Cl* was consistently detectable corresponded to relatively clean conditions, multiday transport over water, and relatively low actinic flux. At high HCl mixing ratios (>1000 pptv), HCl + OH sustained steady state Cl‐atom concentrations in the range of 104 cm−3. When detectable, photolysis of Cl* was generally the dominant source of atomic Cl; steady state concentrations of Cl atoms were frequently in the range of 104 to 105 cm−3. At these concentrations, Cl played an important role in the chemical evolution of polluted coastal air. Br radical chemistry was relatively unimportant.
Breaking waves produce bubble plumes that burst at the sea surface, injecting primary marine aerosol (PMA) highly enriched with marine organic carbon (OC) into the atmosphere. It is widely assumed ...that this OC is modern, produced by present-day biological activity, even though nearly all marine OC is thousands of years old, produced by biological activity long ago. We used natural abundance radiocarbon (
C) measurements to show that 19 to 40% of the OC associated with freshly produced PMA was refractory dissolved OC (RDOC). Globally, this process removes 2 to 20 Tg of RDOC from the oceans annually, comparable to other RDOC losses. This process represents a major removal pathway for old OC from the sea, with important implications for oceanic and atmospheric biogeochemistry, the global carbon cycle, and climate.
Marine aerosols produced by bursting bubbles at the ocean surface are highly enriched in organic matter (OM) relative to seawater. The importance of this OM in the photochemical evolution of marine ...aerosols, particularly as a source of reactive oxidants, is unknown but likely significant. To investigate oxidant production, nascent aerosols were generated by bubbling zero air through flowing Sargasso seawater and photochemical production of OH radical and hydroperoxide were quantified in aqueous aerosol extracts exposed to solar radiation. Extrapolation to ambient conditions indicates that OM photolysis was the primary in situ source for both OH (1.1 × 10−8 M s−1) and hydroperoxides (1.7 × 10−8 M s−1) in nascent aerosols; NO3− photolysis was the primary source in aged, acidified aerosols (1.4 × 10−7 and 4.1 × 10−8 M s−1, respectively). In situ OH photoproduction was comparable to gas‐phase uptake whereas H2O2 photoproduction was slower. Results provide important constraints for poorly quantified oxidant sources in marine aerosols.
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