Concentrations Of Methanesulfonate Research Articles

Relationships among aerosol constituents from Asia and the North Pacific during PEM‐West A

Aerosol particle samples collected from Asia and the North Pacific were analyzed to investigate the relationships among atmospheric sea salt, mineral aerosol, biogenic emissions (methanesulfonate (MSA)), and several anthropogenic substances (sulfate, nitrate, and various trace elements). These studies specifically focused on the sources for aerosol SO4= and on the long‐range transport of continental materials to the North Pacific. Ground‐based aerosol sampling was conducted at four coastal‐continental sites: Hong Kong, Taiwan, Okinawa, and Cheju; and at three remote Pacific islands, Shemya, Midway, and Oahu. Non‐sea‐salt (nss) SO4= and MSA were uncorrelated at the East Asian sites presumably because pollution sources overwhelm the biogenic emissions of nss SO4=. At the coastal‐continental sites, marine biogenic emissions accounted for only 10 to <5% of the total nss SO4=. In contrast, over the ocean the concentrations of nss SO4= and MSA were correlated (Midway r = 0.70; Oahu r = 0.59), and higher percentages of biogenic nss SO4= occurred, 55 and 70% at Oahu and Midway, respectively. The concentrations of nss SO4= and NO3− were correlated at Cheju, Hong Kong, Taiwan, Okinawa, Midway, and Oahu, indicating some similarities in their sources and the processes governing their transport; however, differences in the nss SO4=/NO3− ratios among sites suggest regional differences in the pollution component of the aerosol. At Shemya the concentrations of MSA during the summer (100 ng m−3 or more) are about 2 orders of magnitude higher than those in winter. The dimethylsulfide‐derived fraction of the nss SO4= is highest in the summer when the monthly median nss SO4=/MSA ratios range from 2.7 to 4.5, i.e., comparable to the ratios observed over Antarctica and other high‐latitude locations. However, the monthly median nss SO4=/MSA ratios increase, reaching 50 to 200 in the winter as productivity nearly ceases, and the biogenic fraction of nss SO4= at Shemya decreases dramatically; this suggests a strong seasonal pollution component to the sulfate aerosol. The meteorological conditions favoring the long‐range transport of Asian dust to the North Pacific also lead to transport of anthropogenic materials. At Oahu the correlation between NO3− and Al (dust) was highly significant (r = 0.75; p < 0.001), while the correlations between nitrate and Al at the continental sites were low. These differences indicate that the composition of the air sampled at the coastal‐continental stations may be quite different from the air transported to the remote ocean. This phenomenon also appeared to affect the relationship between nss SO4= and antimony. The correlations between nss SO4= and Sb were weak at the Asian sites but strong at the open ocean sites where the nss SO4=/Sb ratios were higher than those over the continent.

Sources of aerosol nitrate and non-sea-salt sulfate in the Iceland region

Daily aerosol filter samples were collected on Heimaey, Iceland (63.40° N, 20.30° W), beginning in July 1991. Samples were analyzed for NO3−, non-sea-salt (nss) SO42−, and methanesulfonate (MSA). Along with SO2 and nss-SO42−, MSA is a product of the atmospheric oxidation of dimethyl sulfide (DMS) that is produced by marine organisms. For much of the time, concentrations of aerosol nss-SO42− and NO3− were relatively low. Occasionally, however, concentrations increased sharply, by an order of magnitude or more, often for periods of several days. These concentration peaks were usually associated with the presence of a high-pressure field over western Europe; the large-scale wind fields associated with the high pressure subsequently transported pollutants to the Iceland region. The 2-year mean NO3− aerosol concentration was 0.239 μg/m3, while that for nss-SO42− was 0.642 μg/m3; the median values were, respectively, 0.113 μg/m3 and 0.367 μg/m3. Excluding the high-aerosol events (i.e. about 10% of the samples), the NO3− average was 0.131 μg/m3 and that for nss SO42− was 0.385 μg/m3; these values are similar to those measured in the pristine South Pacific. Thus, although pollution events were relatively infrequent, they had a substantial impact on atmospheric chemistry in this region, in effect doubling the annual mean concentrations. There was a very strong seasonal cycle in MSA concentrations, with a summer maximum of about 500 ng/m3, which decreased to a few ng/m3 in December. The seasonal cycle of MSA matches that ofPhaeocystis pouchetii andEmiliania huxleyi, both of which are strong DMS producers; intense and widespread blooms of these organisms are often found around Iceland in the late spring and summer. During the summer, the nss-SO42−MSA ratio was very low much of the time, suggesting that biogenic DMS was the dominant source of aerosol nss-SO42− in this region in this season.

Biogenic sulfur aerosol in the Arctic troposphere: 2. Trends and seasonal variations

An 11‐year record of tropospheric aerosol methanesulfonate (MSA) in the Canadian high Arctic at Alert, Northwest Territories, from 1980 to 1991 shows marked seasonal and long‐term variations. By using spectral‐analysis techniques, the seasonal cycles and long‐term variations have been quantified. There are two distinctly different seasonal peaks with levels of 12–23 ng m−3 in early May and 6–18 ng m−3 in July‐August. Over the 11.3 years, the amplitudes of the MSA seasonal cycles and therefore the annual means of MSA concentrations decreased significantly by 33% (3% annually). So far there is no evidence of experimental artifact in this trend, but such a possibility will be further examined. Analysis of MSA monthly anomalies suggests that in spring they are weakly but significantly related to sea surface temperature anomalies (SSTA) in the North Atlantic west of the coast of continental Europe. In summer, MSA monthly anomalies are significantly correlated with SSTA in oceanic regions further north in the North Atlantic off the coast of Norway and in the northeast North Pacific.

Seasonal variation of methanesulfonic acid in precipitation at Amsterdam island in the southern Indian Ocean

A 29-month record of methanesulfonate (MSA) concentration in 103 rainwater samples has been performed at Amsterdam Island in the southern Indian Ocean. Rain water MSA concentrations range from 0.008 to 1.150 μeq l −1 with a mean value of 0.187 ± 0.054 μeq l −1. A strong seasonal variation in rain water MSA concentration was found with a minimum in winter and a maximum in summer, similar to that observed for atmospheric DMS concentrations measured during the same period. The annual average MSA wet deposition during the studied period was 0.51 μeq m −2 d −1 which represents roughly 20% of the annual average DMS flux.

Dimethylsulfide, aerosols, and condensation nuclei over the tropical northeastern Atlantic Ocean

Concentration of dimethylsuifide (DMS) in seawater, concentrations of DMS and sulfur dioxide (SO2) in the atmosphere, concentrations of methanesulfonate (MSA) and non‐sea‐salt sulfate (nss‐SO42−) in size‐segregated aerosols, and number concentration of condensation nuclei (CN) were measured during September and October 1991 in the northern tropical Atlantic Ocean in order to assess the role of DMS in CN production over this oceanic area. Radon‐222 activity and aerosol ionic composition were used to distinguish air masses with oceanic, continental, and/or polluted characters. No obvious covariation appeared between DMS and its oxidation products (SO2, H2SO4, and MSA) over the whole period of the experiment. However, the division of data into subsets according to continental tracer information allowed us to show that SO2 and nss‐SO4 concentrations correlated with DMS concentration in unpolluted air masses. MSA and nss‐SO42− were found to be mainly concentrated in particles with diameters < of 0.6 μm. Daily mean nss‐SO42− in the <0.6‐μm‐diameter range and CN concentration were correlated (R = 0.91, n = 17, P < 0.001), which suggests that H2SO4 is an important CN precursor. Atmospheric DMS and CN number daily mean concentrations also correlated (R = 0.82, n = 21, P < 0.001). However, the CN population was strongly influenced by continental inputs less than 500 km downwind of Africa, whereas DMS seemed to be able to affect the CN number concentration at about 1500 km from this continent.

Nitrogen and sulfur species in Antarctic aerosols at Mawson, Palmer Station, and Marsh (King George Island)

High volume bulk aerosol samples were collected continuously at three Antarctic sites: Mawson (67.60° S, 62.50° E) from 20 February 1987 to 6 January 1992; Palmer Station (64.77° S, 64.06° W) from 3 April 1990 to 15 June 1991; and Marsh (62.18° S, 58.30° W) from 28 March 1990, to 1 May 1991. All samples were analyzed for Na+, SO 4 2− , NO 3 − , methanesulfonate (MSA), NH 4 + ,210Pb, and7Be. At Mawson for which we have a multiple year data set, the annual mean concentration of each species sometimes vary significantly from one year to the next: Na+, 68–151 ng m−3; NO 3 − , 25–30 ng m−3; nss SO 4 2− , 81–97 ng m−3; MSA, 19–28 ng m−3; NH 4 + , 16–21 ng m−3;210Pb, 0.75–0.86 fCi m−3. Results from multiple variable regression of non-sea-salt (nss) SO 4 2− with MSA and NO 3 − as the independent variables indicates that, at Mawson, the nss SO 4 2− /MSA ratio resulting from the oxidation of dimethylsulfide (DMS) is 2.80±0.13, about 13% lower than our earlier estimate (3.22) that was based on 2.5 years of data. A similar analysis indicates that the ratio at Palmer is about 40% lower, 1.71±0.10, and more comparable to previous results over the southern oceans. These results when combined with previously published data suggest that the differences in the ratio may reflect a more rapid loss of MSA relative to nss SO 4 2− during transport over Antarctica from the oceanic source region. The mean210Pb concentrations at Palmer and Marsh and the mean NO 3 − concentration at Palmer are about a factor of two lower than those at Mawson. The210Pb distributions are consistent with a210Pb minimum in the marine boundary layer in the region of 40°–60° S. These features and the similar seasonalities of NO 3 − and210Pb at Mawson support the conclusion that the primary source regions for NO 3 − are continental. In contrast, the mean concentrations of MSA, nss SO 4 2− , and NH 4 + at Palmer are all higher than those at Mawson: MSA by a factor of 2; nss SO 4 2− by 10%; and NH 4 + by more than 50%. However, the factor differences exhibit substantial seasonal variability; the largest differences generally occur during the austral summer when the concentrations of most of the species are highest. NH 4 + /(nss SO 4 2− +MSA) equivalent ratios indicate that NH3 neutralizes about 60% of the sulfur acids during December at both Mawson and Palmer, but only about 30% at Mawson during February and March.

The first Greenland ice core record of methanesulfonate and sulfate over a full glacial cycle

Methanesulfonate (MSA) in ice cores has attracted attention as a possible tracer of past oceanic emissions of dimethylsulfide (DMS). After sulfate MSA is the second most prevalent aerosol oxidation product of DMS, but in contrast to sulfate, DMS oxidation is the only known source of MSA. The hypothesis by Charlson et al., [1987] of a climate feedback mechanism with sulfur emissions from marine phytoplankton influencing the cloud albedo adds to the interest in establishing long records of MSA and non‐seasalt sulfate spanning large climatic changes. Records of MSA and non‐seasalt sulfate covering time periods from a few years to thousands of year have been extracted from antarctic ice cores [Ivey et al., 1986; Saigne and Legrand, 1987; Legrand and Feniet‐Saigne, 1991; Mulvaney et al., 1992] but only the record from the Vostok ice core [Legrand et al., 1991] covers a full glacial cycle. The concentrations of MSA and non‐seasalt sulfate in Antarctica have been found to increase under glacial conditions. Here we present the first Northern Hemisphere record of MSA, and the first continuous record of non‐seasalt sulfate, both extracted from the Renland ice core, East Greenland. The records are extending from the Holocene to the Eem interglacial 130,000 years B.P. The contrast to the Southern Hemisphere records is striking, with a decreasing concentration of MSA with the advance of glaciation but an increasing concentration of non‐seasalt sulfate. A strong linear relationship is found in the Renland ice core between the ratio of MSA to non‐seasalt sulfate and the temperature, with higher ratios associated with warmer climatic stages, while the opposite relationship to temperature is found in the Vostok ice core. A more complicated picture is emerging of the use of MSA in ice cores as a quantitative tracer which suggests that previous interpretations can have been overly simplistic.

Distribution of methanesulfonate, nss sulfate and dimethylsulfide over the atlantic and the north sea

Abstract The concentrations of aerosol methanesulfonate (MSA) and non-sea-salt (nss) sulfate and of gaseous dimethylsulfide (DMS) were measured simultaneously in the marine atmosphere. Over the Atlantic measurements were performed during two cruises with the research vessel Polarstern between Germany (54°N) and South America (32°S, 42°S). Further sampling sites were located on a research platform and on the island Sylt in the North Sea. MSA concentrations of 1–20 ngS (MSA) m −3 and 5–100 ngS (MSA) m −3 were determined over the Atlantic and North Sea, respectively. On average, the concentration of MSA and its precursor DMS showed a good correlation, with high values being observed especially in spring. Seasonal and diurnal variations of the MSA concentration are discussed. The nss sulfate concentration was quite often influenced by advection of sulfate from continental sources. Under remote marine conditions the concentration ratio of nss sulfate and MSA ranged from 3 to 22.

Airborne measurements of dimethylsulfide, sulfur dioxide, and aerosol ions over the Southern Ocean South of Australia

Vertical distributions of dimethylsulfide (DMS), sulfur dioxide (SO2), aerosol methane-sulfonate (MSA), non-sea-salt sulfate (nss-SO42-), and other aerosol ions were measured in maritime air west of Tasmania (Australia) during December 1986. A few cloudwater and rainwater samples were also collected and analyzed for major anions and cations. DMS concentrations in the mixed layer (ML) were typically between 15–60 ppt (parts per trillion, 10−12; 24 ppt=1 nmol m−3 (20°C, 1013 hPa)) and decreased in the free troposphere (FT) to about <1–2.4 ppt at 3 km. One profile study showed elevated DMS concentrations at cloud level consistent with turbulent transport (‘cloud pumping’) of air below convective cloud cells. In another case, a diel variation of DMS was observed in the ML. Our data suggest that meteorological rather than photochemical processes were responsible for this behavior. Based on model calculations we estimate a DMS lifetime in the ML of 0.9 days and a DMS sea-to-air flux of 2–3 μmol m−2 d−1. These estimates pertain to early austral summer conditions and southern mid-ocean latitudes. Typical MSA concentrations were 11 ppt in the ML and 4.7–6.8 ppt in the FT. Sulfur-dioxide values were almost constant in the ML and the lower FT within a range of 4–22 ppt between individual flight days. A strong increase of the SO2 concentration in the middle FT (5.3 km) was observed. We estimate the residence time of SO2 in the ML to be about 1 day. Aqueous-phase oxidation in clouds is probably the major removal process for SO2. The corresponding removal rate is estimated to be a factor of 3 larger than the rate of homogeneous oxidation of SO2 by OH. Model calculations suggest that roughly two-thirds of DMS in the ML are converted to SO2 and one-third to MSA. On the other hand, MSA/nss-SO42- mole ratios were significantly higher compared to values previously reported for other ocean areas suggesting a relatively higher production of MSA from DMS oxidation over the Southern Ocean. Nss-SO42- profiles were mostly parallel to those of MSA, except when air was advected partially from continental areas (Africa, Australia). In contrast to SO2, nss-SO42- values decreased significantly in the middle FT. NH4+/nss-SO42- mole ratios indicate that most non-sea-salt sulfate particles in the ML were neutralized by ammonium.

Methanesulfonate in rainwater at Cape Grim, Tasmania

Strong seasonal variation in rainwater methanesulfonate (MSA) concentration and wet deposition at Cape Grim is found to parallel the strong seasonal variation in aerosol MSA concentration previously reported for clean, maritime air at this site. The 4 years of rainwater MSA data available from mid-1983 to mid-1987 yield an estimated annual-average wet deposition rate to the ocean surface at 41°S of 0.096 ± 0.047 mmol m -2 year -1 . This annual wet deposition of sulphur in the form of MSA represents only a small fraction (7%) of the 1.3 mmol m -2 yr -1 recently estimated for annual emissions of sulphur (in the form of dimethyl sulfide) from temperate oceans. DOI: 10.1034/j.1600-0889.1990.t01-1-00008.x

Non‐sea‐salt sulfate and nitrate in trade wind aerosols at Barbados: Evidence for long‐range transport

From mid‐May 1984 through December 1987, more than 1100 daily high‐volume bulk aerosol samples were collected during onshore trade winds at Barbados, West Indies. All of these have been analyzed to determine the concentrations of particulate non‐sea‐salt (nss) sulfate, nitrate, and Saharan dust; 91 of the samples were also analyzed for methanesulfonate (MSA). The mean concentrations (in μg m−3) during the period were nitrate, 0.509 (s = 0.389); nss sulfate, 0.751 (s = 0.602); mineral dust, 16.0 (s = 21.1); and MSA, 0.0207 (s = 0.0093). The concentrations of both nitrate and nss sulfate are significantly correlated with those of Saharan dust, indicating that substantial fractions of both are transported across the tropical North Atlantic in association with the dust. This transport accounts for about 60% of the mean total concentration of each of the anions at Barbados. Our data, combined with those from previous studies, indicate that these dust‐related fractions are probably not derived from the Sahara soil material; they are more likely derived from anthropogenic sources. The nitrate‐to‐nss sulfate ratio in this dust‐related fraction changes markedly from the summer to the winter. During the summer the general meteorology and nitrate‐to‐nss sulfate mass ratio (0.36) are consistent with Europe being the major source region; during the winter the ratio increases by a factor of 4 to 1.44, which may be consistent with a source region over southern West Africa. The ratio of the mean MSA concentration to that of the nss sulfate that is not related to dust transport is 0.066, a value similar to the ratio of MSA to total nss sulfate at relatively pristine stations in the Pacific: Fanning Island and American Samoa. The similarity suggests that this fraction of the nss sulfate at Barbados may be derived predominantly from oxidation of reduced sulfur compounds emitted from the ocean. The mean concentration of nitrate that is not related to dust transport is 0.22 μg m−3, about double the total mean concentration over the tropical South Pacific (0.11 μg m−3) and 40% higher than that over the equatorial Pacific (0.16 μg m−3). The major source (or sources) of this nondust‐related nitrate is still very uncertain.

Biogenic sulfur emissions from the Subantarctic and Antarctic Oceans

Measurements of the atmospheric distributions of dimethylsulfide (DMS), sulfur dioxide (SO2), methanesulfonate (MSA), non‐seasalt sulfate (nss‐SO42−), and methylmercaptan (MeSH) were made over the Drake Passage and the coastal and inshore waters west of the Antarctic Peninsula during the 1986 austral fall season. DMS concentrations were also measured in the surface ocean, and vertical profiles were obtained at several locations in the inshore water areas. Surface seawater concentrations of DMS were on the order of 2 nmol L−1, similar to values observed in temperate latitudes. The vertical profiles showed maximum values at depths between 5–40 m. DMS concentrations in the atmosphere were near 4 nmol m−3 (96 parts per trillion by volume, (pptv)), close to the global average for remote oceanic regions. The sea‐to‐air flux of DMS ranged between 1–5 μmol m−2 d−1, with the highest values found in the open ocean areas. The total sea‐to‐air flux of DMS from the Southern Ocean is estimated to be 0.2 Tmol yr −1. MeSH was detected occasionally at concentrations up to 0.15 nmol m−3 (3.6 pptv). The average aerosol MSA concentration (0.27 nmol m−3) was surprisingly high relative to the level of nss‐SO42− (0.31 nmol m−3). Both compounds were found predominantly in fine particles. The nss‐SO42− values were extremely low, comparable to winter values reported for the South Pole. SO2 concentrations were also very low (0.45 nmol m−3 (11 pptv)), consistent with the low levels of nss‐SO42−. The residence time of DMS in the Antarctic marine atmosphere is estimated to be about 2–3 days during clear weather and about 6–7 days during overcast conditions. Photooxidation of DMS in the Southern Ocean atmosphere may lead to a higher yield of MSA and a lower yield of SO2 compared to other world ocean areas.