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Popular summary: Atmospheric aerosols play an important role in the Earth's climate system, and can also have adverse effects on air quality and human health. The environmental impacts of aerosols, on the other hand, are highly regional, since their temporal/spatial distribution is inhomogeneous and highly depends on the regional emission sources. To better understand the effects of aerosols, intensive field experiments are necessary to characterize the chemical and physical properties on a region-by-region basis. From late February to early May in 2006, NASA/GSFC's SMARTLabs facility was deployed at a rural site in central Thailand, Southeast Asia, to conduct a field experiment dubbed BASE-ASIA (Biomass-burning Aerosols in South East-Asia: Smoke Impact Assessment). The group was joined by scientists from the University of Hawaii and other regional institutes. Comprehensive measurements were made during the experiment, including aerosol chemical composition, optical and microphysical properties, as well as surface energetics and local . meteorology. This study analyzes part of the data from the BASE-ASIA experiment. It was found that, even for the relatively remote rural site, the aerosol loading was still substantial. Besides agricultural burning in the area, industrial pollution near the Bangkok metropolitan area, about 200 km southeast of the site, and even long-range transport from China, also contribute to the area's aerosol loading. The results indicate that aerosol pollution has developed into a regional problem for northern Indochina, and may become more severe as the region's population and economy continue to grow. Abstract: Comprehensive measurements of atmospheric aerosols were made in Phimai, central Thailand (15.l83 N, 102.565 E, elevation: 206 m) during the BASE-ASIA field experiment from late February to early May in 2006. The observed aerosol loading was sizable for this rural site (mean aerosol scattering: 108 +/- 64 Mm(exp -1); absorption: 15 +/- 8 Mm(exp -1); PM(sub 10) concentration: 33 +/- 17 miro-g/ cubic m and dominated by submicron particles. Major aerosol compounds included carbonaceous (OC: 9.5 +/- 3.6miro-g/ cubic m; EC: 2.0 2.3 miro-g/ cubic m and secondary species (SO4(2-): 6.4 +/- 3.7 miro-g/ cubic m, NH4(+): 2.2 +/- 1.3 miro-g/ cubic m). While the site was seldom under the direct influence of large forest fires to its north, agricultural fires were ubiquitous during the experiment, as suggested by the substantial concentration of K+ (0.56 +/- 0.33 micro-g/ cubic m). Besides biomass burning, aerosols in Phimai during the experiment were also strongly influenced by industrial and vehicular emissions from the Bangkok metropolitan region and long-range transport from southern China. High humidity played an important role in determining the aerosol composition and properties in the region. Sulfate was primarily formed via aqueous phase reactions, and hygroscopic growth could enhance the aerosol light scattering by up to 60%, at the typical morning RH level of 85%. The aerosol single scattering albedo demonstrated distinct diurnal variation, ranging from 0.86 +/- 0.04 in the evening to 0.92 +/- 0.02 in the morning. This experiment marks the first time such comprehensive characterization of aerosols was made for rural central Thailand. Our results indicate that aerosol pollution has developed into a regional problem for northern Indochina, and may become more severe as the region's population and economy continue to grow.

In this paper, we present recent field studies conducted by NASA's SMART-COMMIT (and ACHIEVE, to be operated in 2013) mobile laboratories, jointly with distributed ground-based networks (e.g., AERONET, http://aeronet.gsfc.nasa.gov/ and MPLNET, http://mplnet.gsfc.nasa.gov/) and other contributing instruments over northern Southeast Asia. These three mobile laboratories, collectively called SMARTLabs (cf. http://smartlabs.gsfc.nasa.gov/, Surface-based Mobile Atmospheric Research & Testbed Laboratories) comprise a suite of surface remote sensing and in-situ instruments that are pivotal in providing high spectral and temporal measurements, complementing the collocated spatial observations from various Earth Observing System (EOS) satellites. A satellite-surface perspective and scientific findings, drawn from the BASE-ASIA (2006) field deployment as well as a series of ongoing 7-SEAS (2010-13) field activities over northern Southeast Asia are summarized, concerning (i) regional properties of aerosols from satellite and in situ measurements, (ii) cloud properties from remote sensing and surface observations, (iii) vertical distribution of aerosols and clouds, and (iv) regional aerosol radiative effects and impact assessment. The aerosol burden over Southeast Asia in boreal spring, attributed to biomass burning, exhibits highly consistent spatial and temporal distribution patterns, with major variability arising from changes in the magnitude of the aerosol loading mediated by processes ranging from large-scale climate factors to diurnal meteorological events. Downwind from the source regions, the tightly coupled-aerosolecloud system provides a unique, natural laboratory for further exploring the micro- and macro-scale relationships of the complex interactions. The climatic significance is presented through large-scale anti-correlations between aerosol and precipitation anomalies, showing spatial and seasonal variability, but their precise cause-and-effect relationships remain an open-ended question. To facilitate an improved understanding of the regional aerosol radiative effects, which continue to be one of the largest uncertainties in climate forcing, a joint international effort is required and anticipated to commence in springtime 2013 in northern Southeast Asia.

Lagrangian time series of dimethylsulfide (DMS) concentrations from a cyclonic and an anticyclonic eddy in the Sargasso Sea were used in conjunction with measured DMS loss rates and a model of vertical mixing to estimate gross DMS production in the upper 60 m during summer 2004. Loss terms included biological consumption, photolysis, and ventilation to the atmosphere. The time- and depth (0–60 m)-averaged gross DMS production was estimated to be 0.73±0.09 nM d −1 in the cyclonic eddy and 0.90±0.15 nM d −1 in the anticyclonic eddy, with respective DMS replacement times of 5±1 and 6±1 d. The higher estimated rate of gross production and lower measured loss rate constants in the anticyclonic eddy were equally responsible for this eddy's 50% higher DMS inventory (0–60 m). When normalized to chlorophyll and total dimethylsulfoniopropionate (DMSP), estimated gross production in the anticyclonic eddy was about twice that in the cyclonic eddy, consistent with the greater fraction of phytoplankton that were DMSP producers in the anticyclonic eddy. Higher rates of gross production were estimated below the mixed layer, contributing to the subsurface DMS maximum found in both eddies. In both eddies, gas exchange, microbial consumption, and photolysis were roughly equal DMS loss terms in the surface mixed layer (0.2–0.4 nM d −1 ). Vertical mixing was a substantial source of DMS to the surface mixed layer in both eddies (0.2–0.3 nM d −1 ) owing to the relatively high DMS concentrations below the mixed layer. Estimated net biological DMS production rates (gross production minus microbial consumption) in the mixed layer were substantially lower (by almost a factor of 3) than those estimated in a previous study of the Sargasso Sea, which may explain the relatively low mixed-layer DMS concentrations found here during July 2004 (∼3 nM) compared to previous summers (∼4–6 nM).

ACE-Asia was a multi-national collaboration organized to investigate and understand the chemistry, radiative properties, and climatic effects of mineral dust and other aerosol particles in the East Asia/Northwest Pacific region. Studies conducted at the Gosan and Zhenbeitai surface supersites show striking variations in aerosol concentrations and properties that were affected by the occurrence and origins of the Asian dust storms, air mass pathways, and mixing during the transport. Investigations conducted on the R/V Ronald H. Brown (RHB) showed that dust had a pervasive influence on the chemical composition, size distribution, and optical properties of the aerosol. Analyses using an aerosol time-of-flight mass spectrometer on the RHB showed that most of the coarse-particle nitrate and sulfate in post-frontal air was associated with dust, and more remarkably, that competitive or exclusionary processes evidently are involved in the uptake or production of these substances. Studies conducted onboard the NCAR C-130 aircraft showed that coarse-mode dust was less absorbing and less hygroscopic than pollution aerosol and that there was little correlation in light scattering and absorption by the sub- vs. super-micrometer aerosol. Below ∼2 km, dust was commonly mixed with pollutants, and this had a stronger influence on the optical properties of the submicrometer particles than the coarse-mode dust; at higher altitudes, the dust was less affected by pollution. Single particle analyses of C-130 samples showed that the mixing of black carbon (BC) with dust was common, but only certain types of BC particles were aggregated. Models were used in the planning, execution and interpretative phases of ACE-Asia; and summaries of modeling results are presented to illustrate the progress being made in identifying new dust sources; in depicting the time-varying, three-dimensional structure of dust plumes; and in quantifying the production, transport, and deposition of Asian dust.

The semi-volatile nature of carbonaceous aerosols complicates their collection, and for this reason special air sampling configurations must be utilized. ACE-Asia provided a unique opportunity to compare different sampling techniques for collecting carbonaceous aerosols. In this paper detailed comparisons between filter-based carbonaceous aerosol sampling methods are made. The majority of organic carbon (OC) present on a backup quartz fiber filter (QFF) in an undenuded-filter sampler resulted from the adsorption of native gaseous OC rather than OC evaporated from collected particles. The level of OC on a backup QFF placed behind a QFF was lower than the level present on a backup QFF placed behind a Teflon membrane filter (TMF) indicating that gas/filter equilibrium may not be achieved in some QFF front and backup filter pairs. Gas adsorption artifacts can result in a 20–100% overestimation of the ambient particle-phase OC concentration. The gas collection efficiency of XAD-coated and carbon-impregnated filter-lined denuders were not always 100%, but, nonetheless, such denuders minimize gas adsorption artifacts. The median fraction of particle-phase OC that is estimated to evaporate from particles collected by denuder-filter samplers ranged from 0 to 0.2; this value depends on the sampler configuration, chemical composition of the OC, and sampling conditions. After properly correcting for sampling artifacts, the measured OC concentration may differ by 10% between undenuded- and denuder-filter samplers. Uncorrected, such differences can be as large as a factor two, illustrating the importance of sampling configurations in which gas adsorption or evaporation artifacts are reduced or can be corrected.

Fog or cloud water (CW) deposition plays an important role in particle scavenging and the delivery of trace constituents to the Earth's surface. In this study, CW concentrations of total dissolvable iron (Fe) and aluminum (Al) were measured in 60 samples spanning 26 individual CW events throughout 1999 in Hawaii Volcanoes National Park on the island of Hawaii. Al concentrations ranged from 8 to 10,489 nM, with a median of 344 nM while Fe concentrations ranged from < 1 to 6419 nM with a median of 32 nM. CW deposition fluxes for Fe and Al ranged from 0.15-0.52 mmol Fe m(-2) yr(-1) and 0.62-1.35 mmol Al m(-2) yr(-1), depending on the estimation method used. The large range in concentrations is higher than expected for a relatively pristine ecosystem. It appears that this inconsistency is due to emissions from the currently active nearby volcano, Kilauea. Categorizing CW events into volcanically versus less or non-volcanically impacted events suggests that although volcanically impacted events only accounted for 12% of fog water deposition, Kilauea Volcano was responsible at least 42% of the measured CW Al deposition and 61% of the CW Fe deposition measured for 1999. (C) 2002 Elsevier Science Ltd. All rights reserved.

The mass concentrations of TSP, PM-10, several secondary aerosol species, and up to 20 elements were determined for bulk aerosol samples collected from four ground-based monitoring sites in XiAn, China. The samples were collected during four seasons from September 1996 to August 1997; and in July 1998. Daily concentrations of TSP, SO2 and NOx from 1995 to 1997 were also obtained from the same sampling sites. Representative concentrations (annual averages) of TSP, SO2 and NOx were 410, 39, 43 μg m−3, respectively. PM-10 accounted for about 60–70% of TSP in summer 1998. The most abundant elements in the samples were Si, Ca, Al, Fe, Cl, P, K and S. A fraction of the Ca, which in typically associated with dust, was from non-crustal sources, especially in coarse particles. In winter, the element with the highest concentration was S, and it was primarily in the form of sulfate. The seasonal mean sulfate concentrations, averaged over all sites, were 100, 340, 59 and 27 μg SO2−4 m−3 for autumn, winter, spring and summer, respectively. The corresponding loadings of ammonium ion were 49, 140, 40 and 17 μg NH4+ m−3 for the same seasons and those for nitrate were 22, 65, 33, 16 μg NO3− m−3. Dispersed sources of coal-combustion (most likely residential heating), as opposed to stationary point sources, evidently play an important role in the large increases in TSP and three-fold increases in sulfate, nitrate and ammonium loading during XiAn's space-heating season.

The measurement of atmospheric aerosol properties (i.e. concentration, size, and composition) from an airborne platform is faced by formidable obstacles. The largest problem is one of getting an undisturbed sample into the aerosol sensor sampling volume or onto a filter for subsequent analysis. The importance of such measurements led to the planning of a workshop to address the difficulties and to assess the present state of airborne aerosol sampling technology. The workshop focused on discussions of observational, experimental and theoretical studies of aerosol inlets. The product of this workshop was a summary of the limitations of sampling inlets currently used for airborne applications and a set of recommendations to overcome these limitations and improve the general quality of such measurements.

A portable permeation tube based system has been developed for the field calibration of nitric acid vapor collection on Nylon filters during actual atmospheric sampling. Extensive testing has been undertaken to determine the effects of: transfer line materials, the uptake of nitric acid on the filter holder apparatus, the linearity of dilution of the nitric acid effusing from the permeation tube source achievable and the effects of the permeation of gases, other than nitric acid, on the permeation tube calibration. Data demonstrating significant uptake of HNO3 on commonly used materials are given, together with specific recommendations on the use of materials to avoid such problems. Nitrogen dioxide is shown to be a significant contaminant of the HNO3 permeation tubes used requiring corrections of the order of 15%. Nitric acid “spiking” during actual field sampling of clean tropospheric air at a remote site in the Rocky Mountains west of Boulder, Colorado demonstrated agreement between the measured Nylon filter nitrate loading and the calculated loading to + 0.1, −0.4 μg at the 60% confidence level. At the atmospheric sampling rate used of 120 std l min−1, these limits correspond to +5, −20 pptv for a one hour sampling time, with proportionately smaller uncertainties on the mean HNO3 mixing ratio for longer sampling times.

Gas samples were collected by aircraft entering volcanic eruption clouds of three Guatemalan volcanoes. Gas chromatographic analyses show higher H2 and S gas contents in ash eruption clouds and lower H2 and S gases in vaporous gas plumes. H isotopic data demonstrate lighter isotopic distribution of water vapor in ash eruption clouds than in vaporous gas plumes. Most of the H2O in the vaporous plumes is probably meteoric. The data are the first direct gas analyses of explosive eruptive clouds, and demonstrate that, in spite of atmospheric admixture, useful compositional information on eruptive gases can be obtained using aircraft.

The acidity of dry air south of a warm front was measured before it ascended producing a large area of warm frontal precipitation. Comparison of the chemical compositions of the dry air and precipitation at cloud base suggest a significant production of both sulfuric and nitric acids in the cloud. Below-cloud processes did not appear to significantly affect the concentration of acids in rain at ground level. Rates of nitric acid and sulfuric acid production in the cloud are estimated.

The average contribution of SO2 to the atmosphere by volcanoes, estimated largely by extrapolation from direct measurements of volcanic SO2, is calculated to be 18.7 Tg per year. Of this, an estimated 6.8 Tg per year (36%) is from non-erupting degassing volcanoes. Erupting volcanoes yield an average annual flux estimated to be 11.9 Tg SO2 per year (64%). The estimated total annual SO2 output is about 23% larger than the most recent estimate based on direct measurements. Our calculations suggest that 64% of the total comes from erupting volcanoes, as compared to 7% in the earlier estimate. Of the total worldwide annual SO2 flux, 9% is found to be from volcanoes.

Summary A d.c. and a.c. polarographic study of the cyclooctatetraene system in dimethyl-formamide-tetrabutylammonium perchlorate is presented. Rate parameters are obtained for the reduction at mercury of cyclooctatetraene, the cyclooctatetraene anion radical and 1,3,5-cyclooctatriene, as well as for the homogeneous protonation of the cyclooctatetraene dianion. The results quantitatively confirm previous evidence suggesting a dramatic rate difference associated with the first and second reduction step of cyclooctatetraene. The origin of this phenomenon is discussed.

Discussion de l'article de Reddy et Claassen, sur la validite des donnees obtenues par la collecte simultanee de retombees seches et humides