D. Orsini

A particle-into-liquid collector for rapid measurement of aerosol bulk chemical composition

We report on a new instrument developed for rapid automated on-line and continuous measurement of ambient aerosol bulk com- position.The general approach is based on earlier devices (Khlystov et al. 1995; Simon and Dasgupta 1995) in which ambient particles are mixed with saturated water vapor to produce droplets easily collected by inertial techniques. The resulting liquid stream is analyzed with an ion chromatograph to quantitatively measure the bulk aerosol ionic components. In this instrument, a modified ver- sion of a particle size magnifier (Okuyama et al. 1984) is employed to activate and grow particles comprising the fine aerosol mass. A single jet inertial impactor is used to collect the droplets onto a vertical glass plate that is continually washed with a constant water diluent flow of nominally 0.10 ml min-1

Refinements to the particle-into-liquid sampler (PILS) for ground and airborne measurements of water soluble aerosol composition

An improved particle-into-liquid sampler (PILS) has proven successful in both ground-based and aircraft experiments for rapid measurements of soluble aerosol chemical composition. Major modifications made to the prototype PILS (Aerosol Sci. Technol. 35 (2001) 718) improve particle collection at higher sample flow (15–17 l min � 1 ) while maintaining minimal sample dilution. Laboratory experiments using a fluorescent calibration aerosol aided in designing the present system and characterized the PILS collection efficiency as a function of particle size. Collection efficiency for particle diameters Dp between 0.03 and 10mm is greater than 97%. In addition, the instrument now samples at low pressures (0.3 atmosphere) necessary for airborne measurements up to approximately 8 km in altitude. An ion chromatograph (IC) is coupled to the PILS for direct on-line analysis of the collected sample (hence the name ‘PILS-IC’). Proper selection of columns and eluants allows for 3.5–4 min separation of 9 major inorganic species (Na + , NH4 ,K + ,C a 2+ ,M g 2+ ,C l � ,N O 3 ,N O 2 ,S O 4� ), while acetate, formate, and oxalate, are also possible in 15 min. Any analytical technique capable of continuous online analysis of a liquid sample can be coupled to the PILS for quantitative semi-continuous measurements of aerosol composition. Changes made to the prototype are explained and data from a recent experiment are compared with standard integrated filter measurements. r 2003 Elsevier Science Ltd. All rights reserved.

Intercomparison Study of the Size-Dependent Counting Efficiency of 26 Condensation Particle Counters

ABSTRACT 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.

Inorganic composition of fine particles in mixed mineral dust–pollution plumes observed from airborne measurements during ACE‐Asia

Chemical characteristics of inorganic water-soluble aerosol particles measured in large Asian springtime dust events during the Asian Pacific Regional Characterization Experiment (ACE-Asia) were investigated. Three specific flights (flights 6, 7, and 10) in the Yellow Sea boundary layer with high mineral dust concentrations mixed with pollutants from Asian urban centers are presented. Measurements during a similar campaign, Transport and Chemical Evolution over the Pacific (TRACE-P), in the same region suggested that fine-particle ammonium sulfate and nitrate salts, and potassium, apparently from biomass burning, are common particle ionic constituents in polluted air. Observations from the ACE campaign show similar characteristics and found that the main component of water-soluble mineral dust was Mg 2+ and Ca 2+ . Ion charge balances of measured fine and total aerosol suggest that a significant fraction of the Mg 2+ and Ca 2+ observed were in the form of carbonates. In polluted air mixed with dust that advected directly from large urban regions in roughly half a day to 1 day (flights 6 and 7), much of the fine-particle nitrate and sulfate (approximately 80%) was apparently associated with ammonium or potassium, the rest likely associated with mineral dust. Only air masses that spent 2-5 days over the Yellow Sea (flight 10) had clear evidence of Cl - depletion. Initial mass accommodation coefficients much less than 0.1 for uptake of SO 2 or HNO 3 by mineral dust in urban plumes containing fossil fuel and biomass-burning emissions could explain the observations. The data suggest an accommodation coefficient dependence on relative humidity.

An intercomparison of lidar-derived aerosol optical properties with airborne measurements near Tokyo during ACE-Asia

[1] During the ACE-Asia intensive observation period (IOP), an intercomparison experiment with ground-based lidars and aircraft observations was conducted near Tokyo. On 23 April 2001, four Mie backscatter lidars were simultaneously operated in the Tokyo region, while the National Center for Atmospheric Research C-130 aircraft flew a steppedascent profile between the surface and 6 km over Sagami Bay southwest of Tokyo. The C-130 observation package included a tracking Sun photometer and in situ packages measuring aerosol optical properties, aerosol size distribution, aerosol ionic composition, and SO2 concentration. The three polarization lidars suggested that the observed modest concentrations of Asian dust in the free troposphere extended up to an altitude of 8 km. We found a good agreement in the backscattering coefficient at 532 nm among lidars and in situ 180� backscatter nephelometer observations. The intercomparison indicated that the aerosol layer between 1.6 and 3.5 km was a remarkably stable and homogenous in mesoscale. We also found reasonable agreement between the aerosol extinction coefficients (sa � 0.03 km � 1 ) derived from the airborne tracking Sun photometer, in situ optical instruments, and those estimated from the lidars above the planetary boundary layer (PBL). We also found considerable vertical variation of the aerosol depolarization ratio (da) and a negative correlation between da and the backscattering coefficient (da) below 3.5 km. Airborne measurements of size-dependent optical parameters (e.g., the fine mode fraction of scattering) and of aerosol ionic compositions suggests that the mixing ratio of the accumulation-mode and coarse-mode (dust) aerosols was primarily responsible for the observed variation of da. Aerosol observations during the intercomparison period captured the following three types of layers in the atmosphere: a PBL (surface to 1.2–1.5 km) where fine (mainly sulfate) particles with a low da (<10%) dominated; an intermediate layer (between the top of the PBL and 3.5 km) where fine particles and dust particles were moderately externally mixed, giving moderate da; and an upper layer (above � 3.5 km) where dust dominated, giving a high da (30%). A substantial dust layer between 4.5 and 6.5 km was observed just west of Japan by the airborne instruments and found to have a lidar ratio of 50.4 ± 9.4 sr. This agrees well with nighttime Raman lidar measurements made later on this same dust layer as it passed over Tokyo, which found a lidar ratio of 46.5 ± 10.5 sr. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles

Intercomparison of near real time monitors of PM2.5 nitrate and sulfate at the U.S. Environmental Protection Agency Atlanta Supersite

[1] Five new instruments for semicontinuous measurements of fine particle (PM2.5) nitrate and sulfate were deployed in the Atlanta Supersite Experiment during an intensive study in August 1999. The instruments measured bulk aerosol chemical composition at rates ranging from every 5 min to once per hour. The techniques included a filter sampling system with automated water extraction and online ion chromatographic (IC) analysis, two systems that directly collected particles into water for IC analysis, and two techniques that converted aerosol nitrate or sulfate either catalytically or by flash vaporization to gaseous products that were measured with gas analyzers. During the one-month study, 15-min integrated nitrate concentrations were low, ranging from about 0.1 to 3.5 μg m -3 with a mean value of 0.5 μg m -3 . Ten-minute integrated sulfate concentrations varied between 0.3 and 40 μg m -3 with a mean of 14 μg m -3 . By the end of the one-month study most instruments were in close agreement, with r-squared values between instrument pairs typically ranging from 0.7 to 0.94. Based on comparison between individual semicontinuous devices and 24-hour integrated filter measurements, most instruments were within 20-30% for nitrate (∼0.1-0.2 μg m -3 ) and 10-15% for sulfate (1-2 leg m -3 ). Within 95% confidence intervals, linear regression fits suggest that no biases existed between the semicontinuous techniques and the 24-hour integrated filter measurements of nitrate and sulfate;, however, for nitrate, the semicontinuous intercomparisons showed significantly less variability than intercomparisons amongst the 24-hour integrated filters.