K. Maxwell-Meier

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

Comparison of ozone temporal scales for large urban, small urban, and rural areas in Georgia.

Abstract Ground‐level ozone (O3) time series are characterized by the sum of several distinct temporal scales: long‐term, seasonal, synoptic, diurnal (daily), and intraday variation. In this study, the authors use a Kolmorogov‐Zurbenko filter to separate the 1981–2001 O3 time‐series from many sites in and around Georgia into these various components. The authors compare the temporal components to examine differences between small and large metropolitan areas and between urban and rural areas. They then focus on the synoptic component to define a predominant transport region or airshed for each site.