A filter-based single-wavelength photometer (Particle Soot Absorption Photometer, PSAP) for measuring light absorption by aerosols was modified to measure at three wavelengths, 467 nm, 530 nm, and ...660 nm. The modified and an unmodified photometer were calibrated during the Reno Aerosol Optics Study (RAOS) 2002 against two absorption standards: a photoacoustic instrument and the difference between the extinction and scattering coefficient. This filter-based absorption method has to be corrected for scattering aerosol and transmission changes. A simple function for this was derived from the calibration experiment as a function of transmission and single-scattering albedo. For an unmodified PSAP at typical atmospheric absorption coefficients the algorithm yields about 5-7% lower absorption coefficients than does the usually used method. The three-wavelength PSAP was used for atmospheric measurements both during RAOS and during the New England Air Quality Study (NEAQS).
A volatility tandem differential mobility analyzer (VTDMA) was developed with the intention to measure the fraction of sulfuric acid in marine fine aerosols (Dp less than 150 nm). This work focused ...on the design and calibration of an aerosol conditioner for the standard tandem differential mobility analyzer that heated a selected aerosol sample in a controlled manner while it minimized sample losses due to thermophoresis and diffusion.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The mass and number relationships occurring within the atmospheric dimethylsulfide/cloud condensation nuclei (CCN)/climate system, using simultaneous measurements of particulate phase mass size ...distributions of nss SO4(2-), methanesulfonic acid (MSA), and NH4(+); number size distributions of particles having diameters between 0.02 and 9.6 microns; CCN concentrations at a supersaturation of 0.3 percent; relative humidity; and temperature, obtained for the northeastern Pacific Ocean in April and May 1991. Based on these measurements, particulate nss SO4(2-), MSA, and NH4(+) mass appeared to be correlated with both particle effective surface area and number in the accumulation mode size range (0.16 to 0.5 micron). No correlations were found in the size range below 0.16 micron. A correlation was also found between nss SO4(2-) mass and the CCN number concentration, such that a doubling of the SO4(2-) mass corresponded to a 40 percent increase in the CCN number concentration. However, no correlation was found between MSA mass and CCN concentration.
The accuracy of the estimated radiative forcing of tropospheric sulfate aerosol depends on the quality and spatial coverage of the aerosol chemical, physical, and optical data that serve as input to ...global climate models. To augment the available data and to provide a comparison of measured and calculated optical properties, surface measurements were made of the aerosol light scattering and backscattering coefficients, the number size distribution from 0.02 to 9.6 μm, and chemical mass size distributions during two Pacific Ocean field experiments. All measurements were made on an aerosol sample stream dried to 30% relative humidity and are reported as such. The first experiment took place during the Pacific Sulfur/Stratus Investigation at Cheeka Peak, Washington, in April and May of 1991 (PSI 91). The second occurred as part of the Marine Aerosol and Gas Exchange cruise in February and March of 1992 (MAGE 92) which was conducted from 33°N to 12°S along 140°W. The mass size distributions of nonseasalt sulfate and sodium varied widely both spatially and temporally. The shape of the number size distribution remained fairly constant throughout both experiments with an accumulation mode geometric number mean diameter of 0.19±0.03 μm and a geometric mean standard deviation of 1.4 ± 0.06. Measured light scattering and backscattering ranged from 3.7 to 19×10−6 m−1 and 0.64 to 2.8×106 m−1, respectively, resulting in an average backscattered fraction of 0.15 with a standard deviation of ±0.009. The light scattering and backscattering coefficients were calculated from a Mie model applied to the measured number size distributions. The mean of the calculated scattering values was 3% higher than the mean of the measured values with a 14% variance about the mean. This variance was within the uncertainty of the calculations indicating that the scattering characteristics of the aerosol were parameterized adequately by the model. The calculated backscattering values were about 40% lower than the measured values, however. The calculated light scattering apportioned to nonseasalt sulfate aerosol was 39±17% of the total calculated scatter. The scattering to mass ratio for sulfate aerosol averaged 5.0 m2 g−1 with a standard deviation of ±1.6 m2 g−1 and varied with variability in the number size distribution. Further measurements are needed that will allow for the formation of a global‐scale database to reveal the extent of the variability in the aerosol chemical, physical, and optical properties relevant to climate forcing.
Oxalic acid is the most abundant dicarboxylic acid found in the troposphere, yet there is still no scientific consensus concerning its origins or formation process. Recent studies have suggested ...mechanisms for its formation in cloud water from gaseous precursors. Comparison of the characteristics of oxalic acid and nss sulfate, a chemical with a known in-cloud formation pathway, provides some support for an aqueous formation mechanism for oxalic acid. Analysis of the filters collected from the CIRPAS Twin Otter aircraft during CARMA I, a field campaign designed to study the marine stratocumulus off the coast of Monterey, CA, by a five stage Micro-Orifice Impactor (MOI) revealed a peak in the concentration distribution at a diameter of 0.26–0.44
μm, similar to the size distribution found for nss sulfate and corresponding to the droplet mode in the aerosol size distribution. An air-equivalent average of 2.03±0.47
μg
m
−3 (standard error) of sulfate was observed in the collected marine cloud water, in excess to below-cloud concentrations by 1.16
μg
m
−3 on average. This suggests in-cloud production similar in concentration to previous field campaigns in coastal marine atmospheres. Oxalate was observed in the clouds at air-equivalent concentrations of 0.21±0.04
μg
m
−3, in excess to below-cloud concentrations by 0.14
μg
m
−3 and suggesting an in-cloud production as well. The tentative identification in cloud water of one of the intermediate species in the aqueous oxalate production mechanism lends further support to an in-cloud oxalate source.
During the ACE‐2 field campaign in the summer of 1997 an intensive, ground‐based physical and chemical characterisation of the clean marine and continentally polluted aerosol was performed at Sagres, ...Portugal. Number size distributions of the dry aerosol in the size range 3–10 000 nm were continuously measured using DMPS and APS systems. Impactor samples were regularly taken at 60% relative humidity (RH) to obtain mass size distributions by weighing the impactor foils, and to derive a chemical mass balance by ion and carbon analysis. Hygroscopic growth factors of the metastable aerosol at 60% RH were determined to estimate the number size distribution at a relative humidity of 60%. A size segregated 3‐way mass closure study was performed in this investigation for the first time. Mass size distributions at 60% RH derived from number size distribution measurements and impactors samples (weighing and chemical analysis) are compared. A good agreement was found for the comparison of total gravimetrically‐determined mass with both number distribution‐derived (slope=1.23/1.09; R2>0.97; depending on the parameters humidity growth and density) and chemical mass concentration (slope=1.02; R2= 0.79) for particles smaller than 3 μm in diameter. Except for the smallest impactor size range relatively good correlations (slope=0.86–1.42) with small deviations (R2=0.76–0.98) for the different size fractions were found. Since uncertainties in each of the 3 methods are about 20% the observed differences in the size‐segregated mass fractions can be explained by the measurement uncertainties. However, the number distribution‐derived mass is mostly higher than the chemically and gravimetrically determined mass, which can be explained by sampling losses of the impactor, but as well with measurement uncertainties as, e.g., the sizing of the DMPS/APS.
Airborne measurements of the optical properties of aerosols near the coasts of California and Washington are presented. Parameters examined include the particle light‐scattering coefficient (for both ...total scattering and backscattering), the particle mass light‐scattering efficiency, the hygroscopic growth factor for particle light scattering, and aerosol optical depths computed from vertical profiles of the light‐scattering coefficient. In several instances, the measured values of these parameters differed from commonly accepted values, derived primarily from more polluted airsheds. For example, the aerosol mass scattering efficiency was found to be 2.1 ± 0.3 m2 g−1.
Particle detection efficiency curves for 26 condensation particle counters were determined during a calibration workshop in preparation for the Aerosol Characterization Experiment 1 (ACE1). Three ...different types of commercially available particle counters, the ultrafine condensation particle counter (TSI-3025) and the condensation particle counters (TSI-3010 and TSI-3760 or TS1-7610) were investigated at default temperature and flow settings as well as for other flow rates and temperature differences between the saturator and the condenser. Furthermore, the pulse-height-analysis ultrafine condensation particle counter and a TSI-3010 modified to achieve a higher temperature difference were calibrated. In this study, the large number of particle counters investigated provided the opportunity to obtain a more statistically significant picture of the performance of different particle counters for different operating conditions.
Airborne data are reported on the effect of sea surface temperature and aerosol gradients on the albedo of marine stratocumulus clouds off the coast of central California. Both types of gradients, at ...the magnitudes and spatial scales observed, produce significant and comparable trends in the cloud albedo (∼15% changes over 40 km).
Measurements of the total aerosol mass and ionic composition were obtained for submicrometer (
D
p ⩽ 1.0
μm) aerosol particles from the remote Pacific boundary layer by gravimetric and ion ...chromatography analysis. Discrepancies were found to exist between the absolute mass determined by the separate techniques suggesting aerosol components in addition to sea salt and sulfate particles exist at significant mass concentrations. The gravimetric mass was equal to or significantly larger than the sum of the ionic masses, suggesting additional aerosol components contribute between 0 and 75% of the submicrometer aerosol mass. Measurements of the elemental composition of individual particles by electron microscopy confirmed the presence of mineral and carbonaceous particles which contributed 0–86% of the total number concentration for the particle-size range of interest. The relative number of submicrometer sulfate particles with respect to the total was low during periods with the largest discrepancy between the gravimetric and ionic mass. The amount of water associated with the submicrometer aerosol at 47% relative humidity made up 29% of the total aerosol mass collected on the filters (and 9% of the total mass at 35%). Laboratory studies determined the relative amount of water associated with sea salt, sulfate, and sodium chloride particles on a filter substrate, with sea-salt particles containing 27% water and ammonium sulfate particles containing only 4% water at 40% r.h.
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