2.1. Aerosol Sample Inlet
 Aerosol particles were sampled 18 m above the sea surface through a heated mast that extended 5 m above the aerosol measurement container. The mast was capped with a horizontal inlet nozzle that was rotated into the relative wind to maintain nominally isokinetic flow and minimize the loss of supermicrometer particles. Air entered the inlet through a 5 cm diameter hole, passed through a 7° expansion cone, and then into the 20 cm inner diameter sampling mast. The flow through the mast was 1 m3 min−1. The transmission efficiency for particles with aerodynamic diameters less than 6.5 μm (the largest size tested) is greater than 95% [Bates et al., 2002].
 The bottom 1.5 m of the mast and the humidity controlled chamber containing the impactors, nephelometers, and sizing instruments were heated or cooled to establish a stable reference relative humidity (RH) for the sample air of ≈60%. A stable reference RH allows for constant instrumental size segregation in spite of variations in ambient RH and results in chemical, physical, and optical measurements which are directly comparable. In addition, measurement at a constant reference RH makes it possible, with the knowledge of appropriate growth factors, for end users of the data set (process, chemical transport, and radiative transfer models) to adjust the measured parameters to a desired relative humidity. A reference RH of 60% was chosen because it is above the crystallization humidity of most aerosol components and component mixtures [Carrico et al., 2003]. For the atmospheric conditions encountered during TexAQS-GoMACCS 2006, it was possible to maintain the humidity controlled chamber at 58 ± 3.4% RH while heating the aerosol 2.5 ± 2.6°C (range −8 to +8°C) above the ambient temperature. The mean temperature in the chamber was 32.8 ± 1.4°C. For the continuous flow instruments discussed below (e.g., AMS, PILS-IC, PILS-WSOC, semicontinuous OC) the aerosol was heated for approximately 2 s.
2.2. Aerosol Chemical Composition
2.2.1. Impactor Sample Collection for Chemical Analysis
 Twenty one 1.6 cm outer diameter stainless steel tubes extended into the heated portion of the mast. These were connected to the aerosol instrumentation and impactors with conductive silicon tubing to prevent electrostatic loss of particles or stainless steel tubing for the lines to the impactors used for collection of carbonaceous aerosol and the aerosol mass spectrometer (AMS).
 The airflow to the impactors was controlled so that air was sampled only when the concentration of particles greater than 15 nm in diameter indicated the sample air was free of Ronald H. Brown emissions (i.e., there were no rapid increases in particle concentration), the relative wind speed was greater than 3 m s−1, and the relative wind was forward of the beam.
 One- and two-stage multijet cascade impactors [Berner et al., 1979] were used to determine submicrometer and supermicrometer concentrations of inorganic ions, organic and elemental carbon (OC and EC), and inorganic oxidized material (IOM). The 50% aerodynamic cutoff diameters of the impactors, D50,aero, were 1.1 and 10 μm. The RH of the sampled air stream was measured a few inches upstream from the impactors. Throughout the paper submicrometer refers to particles with Daero < 1.1 μm at 58 ± 3.4% RH and supermicrometer refers to particles with 1.1 μm < Daero < 10 μm at 58 ± 3.4% RH. Sampling periods ranged from 2 to 14 h for all impactor samples. Blank levels were determined by loading an impactor with substrates but not drawing any air through it.
2.2.2. Impactor Sampling for Inorganic Ions
 Submicrometer and supermicrometer concentrations of Cl−, NO3−, SO4=, methanesulfonate (MSA−), Na+, NH4+, K+, Mg+2, and Ca+2 were determined by ion chromatography (IC) [Quinn et al., 1998]. Non-sea-salt sulfate concentrations were calculated by subtracting sea salt sulfate (based on Na+ concentrations and the ratio of sulfate to sodium in seawater) from the total sulfate. Sea salt aerosol concentrations were calculated as
where 1.47 is the seawater ratio of (Na+ + K+ + Mg+2 + Ca+2 + SO4= + HCO3−)/Na+ [Holland, 1978]. This approach prevents the inclusion of non-sea-salt K+, Mg+2, Ca+2, SO4=, and HCO3− in the sea salt mass and allows for the loss of Cl− mass through Cl− depletion processes. It also assumes that all measured Na+ and Cl− is derived from seawater. Results of Savoie and Prospero  indicate that soil dust has a minimal contribution to measured soluble sodium concentrations.
 Sources of uncertainty in the ionic mass include the air volume sampled (±5%), the extract liquid volume (±3.3%), 2 times the standard deviation of the blank values measured over the course of the experiment, and the precision/calibration of the method (±5%). The average overall uncertainly in the total ionic submicrometer mass was ±8.5%.
2.2.3. Impactor Sampling for Organic and Elemental Carbon
 Submicrometer and sub-10 μm samples were collected using 2 and 1 stage impactors, respectively [Bates et al., 2004]. A denuder was deployed upstream of the submicrometer impactor to remove gas phase organic species. OC and EC concentrations were determined with a Sunset Laboratory thermal/optical analyzer. The thermal program was the same as that used in ACE Asia [Mader et al., 2003; Schauer et al., 2003]. Four temperature steps were used to achieve a final temperature of 870°C in He to drive off OC. After cooling the sample down to 550°C, a He/O2 mixture was introduced and the sample was heated in four temperature steps to 910°C to drive off EC. The transmission of light through the filter was measured to separate EC from any OC that charred during the initial stages of heating. No correction was made for carbonate carbon, so OC includes both organic and carbonate carbon.
 The mass of supermicrometer particulate organic matter (POM) was determined by multiplying the measured organic carbon concentration in μg m−3 by a factor of 2.0. The POM factor is an estimated average of the molecular weight per carbon weight and is based on a review of published measurements of the composition of organic aerosol in urban and nonurban regions [Turpin and Lim, 2001]. On the basis of the range of values given by Turpin and Lim , the POM factor has an uncertainty of ±31%. Note that the submicrometer POM values reported here were obtained from the AMS, not the impactor samples (discussed further in section 3.2.1).
 The uncertainties associated with positive and negative artifacts in the sampling of semivolatile organic species can be substantial and are discussed below. Other sources of uncertainty in the POM mass include the air volume sampled (±5%), 2 times the standard deviation of the blanks measured over the course of the experiment, the precision/calibration of the method (±5%) based on the results of Schauer et al. , and the POM factor (±31%). The average of the quadratic sum of these errors, ignoring positive and negative artifacts, yields an uncertainty of ±13% for OC and ±33% for POM.
 Sources of uncertainty in the EC mass include the air volume sampled (±5%) and the precision/calibration of the method (±13%) based on the results of Schauer et al. . A quadratic sum of these errors involved yields an uncertainty of ±14%.
2.2.4. Impactor Sampling for Inorganic Oxidized Material (Dust)
 Total elemental composition (Na, Mg, Al, Si, P, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ba, As, and Pb) was determined by thin-film X-ray primary and secondary emission spectrometry [Bates et al., 2004]. A component composed of inorganic oxidized material (IOM) was constructed from the elemental data. The IOM most likely was composed of soil dust and/or fly ash. These two components are difficult to distinguish based on elemental ratios. To construct the IOM component, the mass concentrations of Al, Si, Ca, Fe, and Ti, the major elements in soil and fly ash, were combined. It was assumed that each element was present in the aerosol in its most common oxide form (Al2O3, SiO2, CaO, K2O, FeO, Fe2O3, TiO2). The measured elemental mass concentration was multiplied by the appropriate molar correction factor as follows:
[Malm et al., 1994; Perry et al., 1997]. This equation includes a 16% correction factor to account for the presence of oxides of other elements such as K, Na, Mn, Mg, and V that are not included in the linear combination. In addition, the equation omits K from biomass burning by using Fe as a surrogate for soil K and an average K/Fe ratio of 0.6 in soil [Cahill et al., 1986].
 Sources of uncertainty in the IOM mass concentration include the volume of air sampled (±5%), the area of the filter (±5%), 2 times the standard deviation of the blank values measured over the course of the experiment for each element, and the precision of the X-ray analysis [Feely et al., 1991]. The average overall uncertainty in the IOM mass, propagated as a quadratic sum of the errors, was ±12%.
2.2.5. Impactor Sampling for Gravimetrically Determined Mass
 Films and filters were weighed at PMEL with a Cahn Model 29 and Mettler UMT2 microbalance, respectively [Quinn and Coffman, 1998]. The balances are housed in a glove box kept at a humidity of 65 ± 4%. The resulting mass concentrations from the gravimetric analysis include the water mass that is associated with the aerosol at 65% RH. The average uncertainty in submicrometer gravimetric mass, calculated as outlined by Quinn et al. , was ±8.4%.
2.2.6. Aerodyne Mass Spectrometer Sampling of Nonrefractory Aerosol Composition
 Concentrations of submicrometer NH4+, SO4=, NO3−, and POM were measured with a quadrupole aerosol mass spectrometer (Q-AMS) (Aerodyne Research Inc., Billerica, Massachusetts, USA) [Jayne et al., 2000]. The species measured by the AMS are referred to as nonrefractory (NR) and are defined as all chemical components that vaporize at the vaporizer temperature of ∼550°C. This includes most organic carbon species and inorganic species such as ammonium nitrate and ammonium sulfate salts but not mineral dust, elemental carbon, or sea salt. The ionization efficiency of the AMS was calibrated every few days with dry monodisperse NH4NO3 particles using the procedure described by Jimenez et al. . The instrument operated on a 5 min cycle with the standard AMS aerodynamic lens.
 The POM aerosol was divided into two fractions, a hydrocarbon-like organic aerosol (HOA) and an oxygenated organic aerosol (OOA) using a multiple linear regression of the m/z 57 and m/z 44 signals, respectively (algorithm 1 [Zhang et al., 2005]). The regression was conducted on the entire data set and the reconstructed organic concentrations (HOA + OOA) agreed well with the measured values (r2 = 0.97, slope = 0.97). The regression coefficients determined in the AMS mass spectral mode were used to derive the HOA and OOA mass size distributions. A two-component analysis, as conducted here, can underrepresent [Ulbrich et al., 2008] or overrepresent [Lanz et al., 2007] the OOA fraction by up to 20% in cases where more than two components are needed to describe the data set. Although there was no evidence for a wood burning aerosol source (elevated concentrations of non-sea-salt potassium) in the study area, we do not equate HOA and OOA to primary or secondary organic aerosol as the direct emission of oxygenated aerosol species from sources like biomass burning, charbroiling, food cooking cannot be ruled out [Lanz et al., 2007]. A more detailed positive matrix factorization of this data set will be presented in a subsequent manuscript.
 The collection efficiency of the AMS is the product of the transmission of particles through the aerodynamic lens (EL), the efficiency with which particles are focused by the lens and directed to the vaporizer (Es), and the degree to which particles are vaporized and analyzed versus bounced off the vaporizer (EB) [Huffman et al., 2005]. The AMS sampled downstream of an impactor with a 50% aerodynamic cutoff diameter of 1.1 μm. The collection efficiency of the aerodynamic lens, EL, on the AMS inlet, however, is less than 1 for particles with aerodynamic diameters between 500 nm and 1 ìm [Jayne et al., 2000]. Particle losses in this size range were corrected using a linear EL collection efficiency curve (where EL was equal to 100% at 550 nm and 10% at 1000 nm vacuum aerodynamic diameter). The correction added, on average, 14 ± 8% to the AMS total mass.
 The shape-related collection efficiency, ES, depends on the efficiency with which particles are focused by the lens and directed to the vaporizer [Jayne et al., 2000; Huffman et al., 2005]. On the basis of beam width probe data, there was no indication that this factor was different from one for this data set. The collection efficiency due to particle bounce, EB, appears to be a function of particle water content and chemical composition [Allan et al., 2003]. The AMS sampling line coming from the humidity controlled chamber (58 ± 3.4% RH) was controlled to 52 ± 3.2% RH. Pure ammonium nitrate particles, used in the calibration of the instrument have an EB of nearly 1 [Jayne et al., 2000]. Particles with a high percentage of ammonium sulfate have an EB of around 0.5 [Allan et al., 2003; Matthew et al., 2008]. An EB of 0.5 is often used when no other chemical information is available. Comparison of the size corrected (EL) AMS NR sulfate from this cruise with sulfate derived from a particle-into-liquid sampler coupled to an ion chromatograph (PILS-IC) suggests an EB that varied from 1 for acidic sulfate (ammonium to sulfate molar ratio of <0.5) to 0.54 for ammonium sulfate. Therefore, EB was assigned to each 5 min sample based on the AMS ammonium to sulfate molar ratio with EB as an exponential function of the ammonium to sulfate molar ratio varying from 0.54 to 1 for ammonium to sulfate molar ratios of 2 to 0.5. There was no indication from the AMS mass size distributions that the ammonium to sulfate molar ratio varied as a function of size over the accumulation mode size range. A linear regression of 5 min transmission and bounce corrected AMS sulfate concentrations versus PILS-IC sulfate concentrations yielded a slope of 0.95 and an r2 of 0.81. The uncertainty in the AMS concentration measurements during TexAQS/GoMACCS was estimated at ±20%.
2.2.7. PILS Sampling of Water Soluble Organic Carbon
 Water soluble organic carbon (WSOC) was measured with a particle-into-liquid sampler (PILS) [Weber et al., 2001, Orsini et al., 2003] coupled to a Sievers Model 800 Turbo Total Organic Carbon Analyzer [Sullivan et al., 2006]. WSOC is operationally defined as the fraction of particulate organic carbon that is collected in water by the PILS and penetrates a 0.5 μm filter [Sullivan et al., 2004]. The PILS sampled downstream of an impactor with a 50% aerodynamic cutoff diameter of 1.1 μm. A parallel plate carbon denuder was placed upstream of the PILS to remove gas phase organic compounds. The flow was split downstream of the denuder with a 15 l min−1 bypass flow and 15 l min−1 going to the PILS. The sample air was passed through a HEPA filter for 15 min every 45–120 min to remove particles and determine the measurement background. This measurement background was subtracted from the sample air to obtain WSOC concentrations. The water flow coming out of the PILS passed through a 0.5 μm in-line filter to remove particles. The system was standardized by running a dilute liquid sucrose sample through the PILS with the sample air passing through the HEPA filter. Dilution of the sample within the PILS was corrected by directly measuring the water flows through the debubbler, drain, and top of the PILS impactor. Data were recorded every 1 min. The WSOC relative uncertainty was estimated to be between ±20% based on the combined uncertainties associated with air (±5%) and liquid (±5%) flows, calibration (±5%) and background variability (±17%).
2.2.8. PILS Sampling of Inorganic Ions
 Inorganic ions were measured with a PILS coupled to two Metrohm Compact 761 ion chromatographs (IC) operated for the analysis of cations and anions [Weber et al., 2001, Orsini et al., 2003]. The PILS sampled downstream of an impactor with a 50% aerodynamic cutoff diameter of 1.1 μm. The flow was split downstream of the impactor with a 15 l min−1 bypass flow and 15 l min−1 going to two denuders (URG, Inc) located in series after the impactor and upstream of the PILS. One denuder was coated with sodium carbonate to remove gas phase acids and a second denuder was coated with phosphorous acid to remove gas phase bases. The sample air was periodically valved through a HEPA filter to remove particles and determine the measurement background. Samples were collected and analyzed every 5 min. The system was standardized by injecting standard solutions directly into the IC loops. Dilution of the sample within the PILS was corrected by directly measuring the water flows through the debubbler, drain, and top of the PILS impactor.
2.2.9. Sunset Laboratory Semicontinuous Sampling of Organic Carbon
 Organic carbon also was measured with a Sunset Laboratory real-time, semicontinuous thermal/optical carbon analyzer. The instrument sampled downstream of an impactor with a 50% aerodynamic cutoff diameter of 1.1 μm and a parallel plate carbon denuder to remove gas phase organic compounds. The flow was split downstream of the denuder with a 21 l min−1 bypass flow and 9 l min−1 going to the carbon analyzer (filter face velocity = 97 cm s−1). The instrument sampled air for 45 or 105 min depending on the OC concentrations. At the end of the sampling time the instrument analyzed the filter (15 min) using the same temperature program as the laboratory instrument described in section 2.2.3. The concentration of evolved CO2 was measured with an NDIR detector. The sampling times were not sufficient to measure EC above the instrument detection limit (0.35 ìg m−3 based on a 45 min sample time). The sample air was periodically valved through a HEPA filter for the 45 or 105 min sampling time to remove particles and determine the measurement background. Sources of uncertainty for the real-time semicontinuous OC measurement include the air volume sampled (5%), the precision of the method (3%) based on injection of a CH4 standard with each run, and the variability of the background signal (20%). The total uncertainty, excluding positive or negative artifacts, propagated as a quadratic sum of the errors was ±21%.
2.3. Ozone, Sulfur Dioxide, and Carbon Monoxide
 At the base of the sampling mast a 1.4 L min−1 flow was pulled through a 0.32 cm ID, 2 m long Teflon tube into a TECO 49 c ozone analyzer that had been calibrated to a NIST traceable analyzer at NOAA-GMD. Data were recorded in 10 s averages. The detection limit was 2 ppbv and the overall uncertainty was ±2 ppbv + 5%.
 Similarly, at the base of the sampling mast a 0.5 L min−1 flow was pulled through a 0.32 cm inner diameter, 1 m long Teflon tube, a Millipore Fluoropore filter (1.0-μm pore size) housed in a Teflon filter holder, a Perma Pure Inc. Nafion Drier (MD-070, stainless steel, 61 cm long) and then through 2 m of Telfon tubing to a Thermo Environmental Instruments Model 43C Trace Level Pulsed Fluorescence SO2 Analyzer. The initial 1 m of tubing, filter, and drier were located in the humidity-controlled (60%) chamber at the base of the mast. Dry zero air (scrubbed with a charcoal trap) was run through the outside of the Nafion Drier at 1 Lmin−1. Data were recorded in 10 s averages.
 Zero air was introduced into the sample line upstream of the Fluoropore filter for 10 min every 6 h to establish a zero baseline. An SO2 standard was generated with a permeation tube (Vici Metronics, 21.6 ng S min−1 at 40°C). The flow over the permeation tube, diluted to 5.6 ppb, was introduced into the sample line upstream of the Fluoropore filter for 10 min every 24 h. The limit of detection for the 1 min data, defined as 2 times the standard deviation of the signal during the zero periods, was 100 ppt. Uncertainties in the concentrations based on the permeation tube weight and dilution flows was <5%.
 CO was measured with a modified AeroLaser GmbH (Garmisch-Partenkirchen, Germany) AL5002 Ultra-Fast CO analyzer, a commercially available vacuum-UV resonance fluorescence instrument [Gerbig et al., 1999]. Ambient air was sampled from an inlet located approximately 16 m above waterline and 5 m starboard of the aerosol mast inlet; sample air was pulled through a 1.59 cm ID, 10 m long PFA manifold at a flow of 200 lpm to the instrument location. A 0.32 cm ID, 1 m long PFA tap delivered the sample to a Nafion drying tube, which reduced water vapor to less than 0.5 ppth. The CO analyzer then measured the dried air. Mixing ratios were reported for ambient air by correcting for the removed water vapor, using the water vapor mixing ratio measured at the inlet with a Vaisala RH probe. The water mixing ratio was typically 30 ppth (3%) during the campaign, and the correction was always less than 4%. Data were collected at 1 Hz and averaged to 1-min resolution; the total uncertainty was 3%, with a limit of detection of 1.5 ppbv.
2.5. Number Size Distributions
 One of the 21 mast tubes was used to supply ambient air to a short column differential mobility particle sizer (Aitken-DMPS), a medium column differential mobility particle sizer (Accumulation-DMPS) and an aerodynamic particle sizer (APS, TSI model 3321). The two DMPSs were located in a humidity-controlled box (RH = 60%) at the base of the mast. The Aitken-DMPS was a short column University of Vienna [Winklmayr et al., 1991] instrument connected to a TSI 3760A particle counter (TSI, St. Paul, Minnesota) operating with a positive center rod voltage to sample particles with a negative charge. Data were collected in 10 size bins from 20 to 200 nm geometric diameter. The Aitken-DMPS operated with an aerosol flow rate of 1 L min−1and a sheath airflow rate of 10 L min−1. The Accumulation-DMPS was a medium column University of Vienna instrument connected to a TSI 3760A particle counter operating with a positive center rod voltage to sample particles with a negative charge. The aerosol was charged with a Kr85 charge neutralizer (TSI model 3077) upstream of each DMA also at 60% RH. Data were collected in seven size bins from 200 to 800 nm diameter. The Accumulation-DMPS operated with an aerosol flow rate of 0.5 L min−1and a sheath airflow rate of 5 L min−1. The relative humidity of the sheath air for both DMPSs was controlled resulting in a measurement RH in the DMPSs of approximately 60%. With this RH control the aerosol should not have effloresced if it was hydrated in the atmosphere [Carrico et al., 2003]. Mobility distributions were collected every 5 min.
 The mobility distributions were inverted to a number distribution assuming a Fuchs-Boltzman charge distribution from the charge neutralizer. The overlapping channels between the two instruments were eliminated in the inversion. The data were corrected for diffusional losses and size-dependent counting efficiencies. The estimated uncertainty in the number concentration in each bin, based on flow uncertainties was ±10%. The DMPS data were converted from geometric diameters to aerodynamic diameters using calculated densities and the water masses associated with the inorganic ions at the measurement RH. The densities and associated water masses were calculated with a thermodynamic equilibrium model (AeRho) using the measured chemical data [Quinn et al., 2002].
 The APS was located in the lower humidity controlled box (60% RH) at the base of the mast. The inlet to the APS was vertical and its sample withdrawn isokinetically from the larger flow to the DMPS. The APS was modified to minimize internal heating of the sample flow in the APS by its sheath flow and waste heat and thus maintain 60% RH [Bates et al., 2005]. Number size distributions were collected with the APS every 5 min. The APS data were collected in 34 size bins with aerodynamic diameters ranging from 0.96 to 10.37 μm. The APS has been shown to underestimate the size of irregularly shaped particles, such as dust, by an average of 25% [Marshall et al., 1991]. Since dust was a major component of the TexAQS/GoMACCS aerosol, the APS data were corrected for nonspherical particle shape using the dynamic shape factor (1.18) and ultra-Stokesian corrections of Cheng et al.  as summarized by Quinn et al. . The estimated uncertainty in the supermicrometer size distribution was ±10%.
2.6. Seawater DMS
 Seawater entered the ship at the bow, 5.6 m below the ship waterline, and was pumped to the ship laboratory at approximately 30 lpm (water residence time within the ship was <5 min). Every 30 min, a 5 ml water sample was valved from the ship water line directly into a Teflon gas stripper. The sample was purged with hydrogen at 80 ml min−1 for 5 min. DMS and other sulfur gases in the hydrogen purge gas were collected on a Tenax filled trap held at −5°C. During the sample trapping period, 6.2 pmoles of methylethyl sulfide (MES) were valved into the hydrogen stream as an internal standard. At the end of the sampling/purge period the trap was rapidly heated to 120°C and the sulfur gases were desorbed from the trap, separated on a DB-1 megabore fused silica column held at 70°C, and quantified with a sulfur chemiluminesence detector. Between each water sample the system analyzed either a DMS standard or a system blank. The system was calibrated using gravimetrically calibrated DMS and MES permeation tubes. The precision of the analysis has been shown to be ±2% based on replicate analysis of a single water sample at 3.6 nM DMS.
2.7. Back Trajectories
 FLEXPART, a Lagrangian particle dispersion model [Stohl et al., 1998; Stohl and Thomson, 1999], was used to determine the origin of aerosols that had undergone transport to the ship. FLEXPART was driven with model-level data from the European Centre for Medium-Range Weather Forecasts (ECMWF) at a resolution of 0.36° × 0.36° in the area of interest here. The ECMWF model has four levels in the lowest 100 m of the atmosphere and can resolve some of the structure of the marine boundary layer. Backward simulations, as described by Seibert and Frank , were done along the ship track every hour. Every simulation consisted of 40,000 particles released in the volume of air sampled. The backward simulations are done with full turbulence and convection parameterizations. The primary output of FLEXPART is an emission sensitivity, which indicates where and when emissions could have impacted the sampled air mass. The impact of surface emissions on the sampled air mass, for instance, is proportional to the local product of the emission strength and the emission sensitivity at the lowest altitude (the so-called footprint). For the purpose of classifying air masses according to their origin, the emissions sensitivity fields can be interpreted analogous to traditional air mass back trajectories.
2.8. Calculations of Aerosol Water Content
 The chemical thermodynamic equilibrium model AeRho was used to estimate the water mass associated with the inorganic ions at 60% RH and at ambient humidity. It was assumed that the inorganic aerosol was an internal mixture containing all measured ionic species. The chemical reactions included in the model, the crystallization humidities used for the solid phase species, and the method for the calculation of the aerosol water content are given by Quinn et al. . Both the IOM and the organic mass were assumed to not take up any water. AeRho was also used to calculate the refractive index and density for each chemical component based on measured size distributions and chemical composition. To check for internal consistency in the measured and modeled parameters, closure experiments were performed for measured and calculated mass (summarized in section 3.1.3).
2.9. Calculations of Mixing Height
 Mixing heights were calculated using velocity and aerosol data acquired from NOAA's High Resolution Doppler Lidar (HRDL), a 2 μm wavelength, motion stabilized, scanning, coherent, Doppler lidar that provides velocity and signal strength estimates with 30 m line-of-sight range resolution and an update rate of 2 Hz [Grund et al., 2001]. Processing of velocity and backscatter data from various scan sequences provided high vertical resolution (5–30 m) profiles of horizontal mean wind speed and direction, and 30 m vertical resolution profiles of both atmospheric velocity variance and uncalibrated aerosol backscatter. A new set of profiles was acquired once every 15 min during the experiment. In this application, mixing height is defined as the top of the layer in turbulent connection with the surface. For most of the experiment, mixing height was estimated directly from turbulence profiles (S. C. Tucker et al., manuscript in preparation, 2008) by searching for the height in the variance profiles at which surface-connected turbulence dropped below the threshold of 0.04 m2/s2 (20 cm/s). Hourly averages of the mixing heights were used in this study.