Thermodynamic characterization of Mexico City aerosol during MILAGRO 2006

Fast measurements of aerosol and gas-phase constituents coupled with the ISORROPIA-II thermodynamic equilibrium model are used to study the partitioning of semivolatile inorganic species and phase state of Mexico City aerosol sampled at the T1 site during the MILAGRO 2006 campaign. Overall, predicted semivolatile partitioning agrees well with measurements. PM2.5 is insensitive to changes in ammonia but is to acidic semivolatile species. For particle sizes up to 1μm diameter, semi-volatile partitioning requires 15-30 min to equilibrate; longer time is typically required during the night and early morning hours. Aerosol and gas-phase speciation always exhibits substantial temporal variability, so that aerosol composition measurements (bulk or size-resolved) obtained over large integration periods are not reflective of its true state. When the aerosol sulfate-to-nitrate molar ratio is less than unity, predictions improve substantially if the aerosol is assumed to follow the deliquescent phase diagram. Treating crustal species as "equivalent sodium" (rather than explicitly) in the thermodynamic equilibrium calculations introduces important biases in predicted aerosol water uptake, nitrate and ammonium; neglecting crustals further increases errors dramati- cally. This suggests that explicitly considering crustals in the thermodynamic calculations is required to accurately predict the partitioning and phase state of aerosols. © 2009 Author(s).

Hygroscopicity and composition of California CCN during summer 2010

Athanasios Nenes

We present an overview and analysis of cloud condensation nuclei (CCN) sampled in California by a NOAA WP-3D aircraft during the 2010 CalNex project. Four distinct geographical regions are characterized, including the Los Angeles basin, the San Joaquin and Sacramento Valleys, and the eastern Pacific Ocean west of southern California. Median size distributions in the Central Valley were unimodal (Dg ∼ 25nm) with a larger fraction of organic species and smaller fraction of nitrate species in the Sacramento Valley aerosol than in the San Joaquin Valley aerosol. Size distributions in the Los Angeles basin and marine outflow were bimodal (geometric mean diameter, Dg ∼ 30, 90-100nm) with similar organic fractions and some replacement of nitrate with sulfate in the marine outflow. Both fine particle and CCN concentrations were found to decrease rapidly above the planetary boundary layer (∼2 km altitude), with CCN concentrations in the boundary layer ranging from ∼102-104cm-3 STP, while fine particle concentrations (0.004-1 m diameters) ranged from ∼103-10 5 cm-3 STP. The CCN-active number fraction varied between 0-100% in the Los Angeles Basin and Marine Outflow, but was substantially lower (0-40%) in the San Joaquin and Sacramento Valleys. Values of the hygroscopicity parameter, , inferred from the CCN measurements varied from 0.1-0.25, with the highest values in the marine outflow and the lowest values in the Sacramento Valley. The values agreed well with the predictions based on size-resolved aerosol composition, but were overpredicted by almost twofold when size-averaged composition was used. CCN closure was assessed for simplified compositional and mixing state assumptions, and it was found that assuming the aerosol to be internally mixed overpredicted CCN concentrations by 30-75% for all air mass types except within the Sacramento Valley, where good closure (overprediction < 10%) was achieved by assuming insoluble organics. Assuming an externally-mixed aerosol fraction or incorporating size-resolved composition data improved closure in the other three regions, consistent with the bimodal nature of the aerosol size distribution. © 2012 by the American Geophysical Union.

Blackwell Publishing Ltd2012

A multi-year data set on aerosol-cloud-precipitation-meteorology interactions for marine stratocumulus clouds

Athanasios Nenes, Zheng Wang

Airborne measurements of meteorological, aerosol, and stratocumulus cloud properties have been harmonized from six field campaigns during July-August months between 2005 and 2016 off the California coast. A consistent set of core instruments was deployed on the Center for Interdisciplinary Remotely-Piloted Aircraft Studies Twin Otter for 113 flight days, amounting to 514 flight hours. A unique aspect of the compiled data set is detailed measurements of aerosol microphysical properties (size distribution, composition, bioaerosol detection, hygroscopicity, optical), cloud water composition, and different sampling inlets to distinguish between clear air aerosol, interstitial in-cloud aerosol, and droplet residual particles in cloud. Measurements and data analysis follow documented methods for quality assurance. The data set is suitable for studies associated with aerosol-cloud-precipitation-meteorology-radiation interactions, especially owing to sharp aerosol perturbations from ship traffic and biomass burning. The data set can be used for model initialization and synergistic application with meteorological models and remote sensing data to improve understanding of the very interactions that comprise the largest uncertainty in the effect of anthropogenic emissions on radiative forcing. © The Author(s) 2018.

Nature Publishing Groups2018

Toward the determination of joint volatility-hygroscopicity distributions: Development and response characterization for single-component aerosol

Athanasios Nenes

This work presents the development and characterization of a thermodenuder for the study and interpretation of aerosol volatility. Thermodenuder measurements are further combined with a continuous-flow streamwise thermal gradient CCN counter to obtain the corresponding aerosol hygroscopicity. The thermodenuder response function is characterized with monodisperse aerosol of variable volatility and hygroscopicity. The measurements are then interpreted with a comprehensive instrument model embedded within an optimization framework to retrieve aerosol properties with constrained uncertainty. Special attention is given to the interpretation of the size distribution of the thermodenuded aerosol, deconvoluting the effects of impurities and multiple charging, and to simplifications on the treatment of thermodenuder geometry, temperature, the cooling section, and the effects of curvature and accommodation coefficient on inferred particle volatility. Retrieved vapor pressures are consistent with published literature and shown to be most sensitive to uncertainty in the accommodation coefficient. Copyright © 2014 American Association for Aerosol Research.

2014

Hygroscopicity and composition of California CCN during summer 2010

Athanasios Nenes

Blackwell Publishing Ltd2012