Atmospheric Chemistry and Physics Discussions, 2009
−3 ) between 0.2 and 1.0% supersaturation, aerosol size distribution and chemical composition wer... more −3 ) between 0.2 and 1.0% supersaturation, aerosol size distribution and chemical composition were performed at a remote marine site in the eastern Mediterranean, from September to October 2007 during the FAME-07 campaign. Virtually all the particles activate at 0.8% 5 supersaturation, consistent with the very aged nature of the aerosol sampled. Application of Köhler theory, using measurements of bulk composition and size distribution, and assuming that organics are insoluble resulted in agreement between predicted and measured CCN concentrations within 3.4±11% for all supersaturations, with a tendency for CCN underprediction (15±8%; r 2 =0.92) at lower supersaturations (0.2-10 0.4%). Including the effects of the water-soluble organic fraction (which represents around 70% of the total organic content) reduces the underprediction bias at low supersaturations, but introduces a slight overprediction (around 5±15%) bias at higher supersaturations (0.6-0.8%), likely from size-dependent variations of the sulfate to organic ratio. Using threshold droplet growth analysis, the growth kinetics of ambient 15 CCN is consistent with NaCl calibration experiments; hence the presence of aged organics does not suppress the rate of water uptake in this environment. The knowledge of the soluble fraction is sufficient for the description of the CCN activity in this area.
The US Environmental Protection Agency's (EPA) Community Multiscale Air Quality (CMAQ) modeling s... more The US Environmental Protection Agency's (EPA) Community Multiscale Air Quality (CMAQ) modeling system version 4.7 is further developed to enhance its capability in simulating the photochemical cycles in the presence of dust particles. The new model treatments implemented in CMAQ v4.7 in this work include two online dust emission schemes (i.e., the Zender and Westphal schemes), nine dust-related heterogeneous reactions, an updated aerosol inorganic thermodynamic module ISORROPIA II with an explicit treatment of crustal species, and the interface between ISORROPIA II and the new dust treatments. The resulting improved CMAQ (referred to as CMAQ-Dust), offlinecoupled with the Weather Research and Forecast model (WRF), is applied to the April 2001 dust storm episode over the trans-Pacific domain to examine the impact of new model treatments and understand associated uncertainties. WRF/CMAQ-Dust produces reasonable spatial distribution of dust emissions and captures the dust outbreak events, with the total dust emissions of ∼ 111 and 223 Tg when using the Zender scheme with an erodible fraction of 0.5 and 1.0, respectively. The model system can reproduce well observed meteorological and chemical concentrations, with significant improvements for suspended particulate matter (PM), PM with aerodynamic diameter of 10 µm, and aerosol optical depth than the default CMAQ v4.7. The sensitivity studies show that the inclusion of crustal species reduces the concentration of PM with aerodynamic diameter of 2.5 µm (PM 2.5 ) over polluted areas. The heterogeneous chemistry occurring on dust particles acts as a sink for some species (e.g., as a lower limit estimate, reducing O 3 by up to 3.8 ppb (∼ 9 %) and SO 2 by up to 0.3 ppb (∼ 27 %)) and as a source for some others (e.g., increasing fine-mode SO 2− 4 by up to 1.1 µg m −3 (∼ 12 %) and PM 2.5 by up to 1.4 µg m −3 (∼ 3 %)) over the domain. The long-range transport of Asian pollutants can enhance the surface concentrations of gases by up to 3 % and aerosol species by up to 20 % in the Western US.
PMCAMx-2008, a detailed three-dimensional chemical transport model (CTM), was applied to Europe t... more PMCAMx-2008, a detailed three-dimensional chemical transport model (CTM), was applied to Europe to simulate the mass concentration and chemical composition of particulate matter (PM) during May 2008. The model includes a state-of-the-art organic aerosol module which is based on the volatility basis set framework treating both primary and secondary organic components as semivolatile and photochemically reactive. The model performance is evaluated against high time resolution aerosol mass spectrometer (AMS) ground and airborne measurements. Overall, organic aerosol is predicted to account for 32 % of total PM 1 at ground level during May 2008, followed by sulfate (30 %), crustal material and sea-salt (14 %), ammonium (13 %), nitrate (7 %), and elemental carbon (4 %). The model predicts that fresh primary OA (POA) is a small contributor to organic PM concentrations in Europe during late spring, and that oxygenated species (oxidized primary and biogenic secondary) dominate the ambient OA. The Mediterranean region is the only area in Europe where sulfate concentrations are predicted to be much higher than the OA, while organic matter is predicted to be the dominant PM 1 species in cen-Correspondence to: S. N. Pandis (spyros@andrew.cmu.edu) tral and northern Europe. The comparison of the model predictions with the ground measurements in four measurement stations is encouraging. The model reproduces more than 94 % of the daily averaged data and more than 87 % of the hourly data within a factor of 2 for PM 1 OA. The model tends to predict relatively flat diurnal profiles for PM 1 OA in many areas, both rural and urban in agreement with the available measurements. The model performance against the high time resolution airborne measurements at multiple altitudes and locations is as good as its performance against the ground level hourly measurements. There is no evidence of missing sources of OA aloft over Europe during this period.
A module predicting the oxidation state of organic aerosol (OA) has been developed using the two-... more A module predicting the oxidation state of organic aerosol (OA) has been developed using the two-dimensional volatility basis set (2D-VBS) framework. This model is an extension of the 1D-VBS framework and tracks saturation concentration and oxygen content of organic species during their atmospheric lifetime. The host model, a onedimensional Lagrangian transport model, is used to simulate air parcels arriving at Finokalia, Greece during the Finokalia Aerosol Measurement Experiment in May 2008 (FAME-08).
Aerosol Formation and Transport to and from Polluted Megacities
Pollution from megacities and large urban areas is important not only for local effects on health... more Pollution from megacities and large urban areas is important not only for local effects on health, visibility, and ecosystems, but also because of its influence on atmospheric chemistry and radiative forcing in regional scales. We combine in this study results from major field ...
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Papers by C. Fountoukis