K. J. Zarzana

University of Colorado at Boulder, Boulder, Colorado, United States

Are you K. J. Zarzana?

Claim your profile

Publications (9)21 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Accurate refractive index values are required to determine the effects of aerosol particles on direct radiative forcing. Theoretical retrievals using extinction data alone or extinction plus absorption data have been simulated to determine the sensitivity of each retrieval. A range of aerosol types with a range of different refractive indices were considered. The simulations showed that the extinction-only retrieval was not able to accurately or precisely retrieve refractive index values, even for purely scattering compounds, but the addition of a simulated absorption measurement greatly improved the retrieval.Copyright 2014 American Association for Aerosol Research
    Aerosol Science and Technology 11/2014; 48(11). · 2.78 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Knowledge about Rayleigh scattering cross sections is relevant to predictions about radiative transfer in the atmosphere, and needed to calibrate the reflectivity of mirrors that are used in high-finesse optical cavities to measure atmospheric trace gases and aerosols. In this work we have measured the absolute Rayleigh scattering cross-section of nitrogen at 405.8 and 532.2 nm using cavity ring-down spectroscopy (CRDS). Further, multi-spectral measurements of the scattering cross-sections of argon, oxygen and air are presented relative to that of nitrogen from 350 to 660 nm using Broadband Cavity Enhanced Spectroscopy (BBCES). The reported measurements agree with refractive index based theory within 0.2±0.4%, and have an absolute accuracy of better than 1.3%. Our measurements expand the spectral range over which Rayleigh scattering cross section measurements of argon, oxygen and air are available at near-ultraviolet wavelengths. The expressions used to represent the Rayleigh scattering cross-section in the literature are evaluated to assess how uncertainties affect quantities measured by cavity enhanced absorption spectroscopic (CEAS) techniques. We conclude that Rayleigh scattering cross sections calculated from theory provide accurate data within very low error bounds, and are suited well to calibrate CEAS measurements of atmospheric trace gases and aerosols.
    Journal of Quantitative Spectroscopy and Radiative Transfer 11/2014; 147:171–177. · 2.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Light extinction by particles in Earth's atmosphere is strongly dependent on particle size, chemical composition, hygroscopic growth properties and particle mixing state. Here, the influence of an organic coating on particle optical growth was studied. The particle optical growth factor, fRHext, was measured using cavity ring-down aerosol extinction spectroscopy at 532 nm. The particles were composed of ammonium sulfate (AS), 1,2,6-hexanetriol, and mixed particles containing a wet or dry ammonium sulfate core and a 1,2,6-hexanetriol coating. Dry, coated particles were generated by atomization followed by drying. Wet, coated particles were formed via liquid-liquid phase separation (LLPS). LLPS was achieved by deliquescing and then drying the particles to a relative humidity between the phase separation RH and the efflorescence RH. For the LLPS particles, the fRHext at each RH was between the fRHext of ammonium sulfate and 1,2,6-hexanetriol. In contrast, for the mixed dry, coated particles, the fRHext was the same as 1,2,6-hexanetriol particles. At room temperature, the water uptake properties of AS coated with 1,2,6-hexanetriol are largely dictated by the phase of the AS. Thus, the total water uptake depends on the RH history of the particle and the resulting phase of AS.
    Environmental Science & Technology 10/2013; · 5.48 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: At the Rocky Mountain Biogenic Aerosol Study (BEACHON-RoMBAS) field campaign in the Colorado front range, July-August 2011, measurements of gas- and aerosol-phase organic nitrates enabled a study of the role of NOx (NOx = NO + NO2) in oxidation of forest-emitted VOCs and subsequent aerosol formation. Substantial formation of peroxy- and alkyl-nitrates is observed every morning, with an apparent 2.9% yield of alkyl nitrates from daytime RO2 + NO reactions. Aerosol-phase organic nitrates, however, peak in concentration during the night, with concentrations up to 140 ppt as measured by both optical spectroscopic and mass spectrometric instruments. The diurnal cycle in aerosol fraction of organic nitrates shows an equilibrium-like response to the diurnal temperature cycle, suggesting some reversible absorptive partitioning, but the full dynamic range cannot be reproduced by thermodynamic repartitioning alone. Nighttime aerosol organic nitrate is observed to be positively correlated with [NO2] × [O3] but not with [O3]. These observations support the role of nighttime NO3-initiated oxidation of monoterpenes as a significant source of nighttime aerosol. Nighttime production of organic nitrates exceeds daytime photochemical production at this site, which we postulate to be representative of the Colorado front range forests.
    Atmospheric Chemistry and Physics 01/2013; 13(1):1979-2034. · 4.88 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Secondary organic aerosol makes up a significant fraction of the total aerosol mass, and a growing body of evidence indicates that reactions in the atmospheric aqueous phase are important contributors to aerosol formation and can help explain observations that cannot be accounted for using traditional gas-phase chemistry. In particular, aqueous phase reactions between small organic molecules have been proposed as a source of light absorbing compounds that have been observed in numerous locations. Past work has established that reactions between α-dicarbonyls and amines in evaporating water droplets produces particle-phase products that are brown in color. In the present study, the complex refractive indices of model secondary organic aerosol formed by aqueous phase reactions between the α-dicarbonyls glyoxal and methylglyoxal and the primary amines glycine and methylamine have been determined. The reaction products exhibit significant absorption in the visible, and refractive indices are similar to those for light absorbing species isolated from urban aerosol. However, the optical properties are different from the values used in models for secondary organic aerosol, which typically assume little to no absorption of visible light. As a result, the climatic cooling effect of such aerosols in models may be overestimated.
    Environmental Science & Technology 04/2012; 46(9):4845-51. · 5.48 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ambient measurements of NOy (NO2, peroxy- and alkyl-nitrates, and the gas/aerosol partitioning of the latter) and Potential Aerosol Mass measurements of NO3-initiated secondary organic aerosol formation in a 16 L flow-through reactor were made during the BEACHON-RoMBAS field campaign in U.S. Forest Service Manitou Forest Observatory, Colorado (July/August 2011). A cavity ringdown spectrometer (CRDS) is used to monitor NO3 and N2O5 , Thermal Desorption - Laser Induced Fluorescence (TD-LIF) is used to detect the NOy species as NO2; an Aerodyne Aerosol Mass Spectrometer (AMS) monitors chemical composition of aerosol; Proton Transfer Reaction Mass Spectrometry (PTR-TOF-MS) monitors the gas-phase organic compounds; and a thermal converter/chemiluminescent NO/NOx/NH3 analyzer monitors gas-phase inorganic nitrogen compounds. In the PAM measurements, a calibrated flow of NO3 is supplied to the reactor from a temperature-controlled N2O5 trap. With this suite of measurements we seek to elucidate the role of nitrate in biogenic SOA formation, as well as the fate of pollution emissions in a forest environment. We observe significant concentrations of ambient alkyl- and peroxynitrates, despite the remote forest location, and find evidence in PAM measurements that formation of these compounds is linked to organic aerosol production.
    AGU Fall Meeting Abstracts. 12/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: A Potential Aerosol Mass (PAM) photooxidation reactor (Kang et al., ACP 2007, 2010) was used in conjunction with an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (DeCarlo et al. Anal. Chem. 2006; HR-ToF-AMS) to characterize biogenic secondary organic aerosol formation during the July-August 2011 BEACHON-RoMBAS field campaign at the U.S. Forest Service Manitou Forest Observatory, Colorado. The PAM reactor uses mercury lamps to create OH concentrations up to 10,000 times ambient levels. High oxidant concentrations accelerate the photooxidation of volatile organic compounds and inorganic gases, which then partition into the aerosol phase. PAM photochemical processing can represent up to approximately 20 days of equivalent atmospheric aging in the span of 4 minutes of residence time in the reactor, and PAM-processed aerosols have shown similar aging signatures as well as sulfate and SOA yields when compared to aging ambient aerosols (Kang et al., ACP 2010; Lambe et al., ACP 2011). The reactor was also injected with O3 or N2O5 in the absence of lights to investigate oxidation by O3 or NO3, oxidants that are expected to have increased importance at locations dominated by biogenic emissions. Presented here is the analysis of PAM processed aerosols using an HR-ToF-AMS, a Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF-MS), and an NO3/N2O5 instrument. Preliminary results show that PAM photooxidation enhances SOA at intermediate OH exposure (1-10 equivalent days) but results in net loss of OA at very long OH exposure (10-20 equivalent days). PAM oxidation also results in a Van Krevelen diagram (H/C vs. O/C) slope similar to ambient oxidation. Oxidation with NO3 is shown to result in significant SOA production, and both OH and N2O5/NO3 oxidation cause production of NH4NO3 at low nighttime temperatures.
    AGU Fall Meeting Abstracts. 12/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Light extinction by particles is strongly dependent on chemical composition, particle size, and water uptake. Relative humidity affects extinction by causing changes in refractive index and particle size due to hygroscopic growth. The ability of particles to take up water depends on its composition and structure. Organic compounds and inorganic salts are often found to be internally mixed within the same aerosol particle. There is currently a great deal of interest in aqueous particles with an insoluble organic coating. The impact of organic films on particle water uptake is uncertain. Therefore, a systematic study that examines water uptake as a function of the chemical nature, packing structure, and coating thickness is highly desirable. These data are critical to evaluate the aerosol direct effect on climate, which is the most uncertain aspect of future climate change. To determine how tightly packed the organic component is, a range organic compounds with different chain lengths, such as decanoic (C10), myristic (C14), stearic (C18), and docosanoic (C22) acids, were used. Coated aerosols are generated and sized using a TSI constant output atomizer and scanning mobility particle sizer. A cavity ring-down aerosol extinction spectrometer at 532 nm is used to measure the optical growth factor as a function of relative humidity for the internally mixed particles. We explored the relationship between optical growth and packing structure by varying the organic component chain length and working with different coating thicknesses.
    AGU Fall Meeting Abstracts. 12/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Secondary organic aerosol is primarily produced via the oxidation of volatile organic compounds, but can also be formed by aqueous particle-phase accretion reactions. Recently it has been shown that volatile alpha-dicarbonyls such as glyoxal and methylglyoxal can react in aqueous solutions with themselves and with other organic compounds such as amines to form complex light-absorbing oligomers. Recent work has indicated that these reactions could take place in cloud water and other aqueous aerosol solutions and be a significant source of SOA. In order to determine the effects of these particles on radiative forcing, their optical properties, specifically their refractive indices, must be known. This study examines the optical properties of four model systems for cloud condensation reactions: glyoxal and glycine; glyoxal and methylamine; methylglyoxal and glycine; and methylglyoxal and methylamine. Cavity ring-down aerosol extinction spectroscopy, FTIR transmission spectroscopy, and AFM were used to determine both the real and imaginary parts of the refractive indices of these systems.
    AGU Fall Meeting Abstracts. 12/2010;