Despite the substantial improvements in the measurements of aerosol physical and chemical properties and in the direct and indirect radiative effects of aerosols, there is still a need for studying the properties of aerosols under controlled laboratory conditions to develop a mechanistic and quantitative understanding of aerosol formation, chemistry, and dynamics. In this work, we present the factors that affect measurement accuracy and the resulting uncertainties of the extinction-minus-scattering method using a combination of cavity ring-down spectroscopy (CRDS) and integrating nephelometry at a wider range of optical wavelengths than previously attempted. Purely scattering polystyrene latex (PSL) spheres with diameters from 107-303 nm and absorbing polystyrene spheres (APSL) with 390 nm diameter were used to determine the consistency and agreement, within experimental uncertainties, of CRDS and nephelometer values with theoretical calculations derived from Mie theory for non-absorbing spheres. Overall uncertainties for extinction cross-section were largely 10%-11% and dominated by condensation particle counter (CPC) measurement error. Two methods for determining σ ext error are described, and they were found to produce equivalent results. Systematic uncertainties due to particle losses, RD cell geometry (R L ), CPC counting efficiency, ring-down regression fitting, blank drift, optical tweezing, and recapturing of forward scattered light are also investigated. The random error observed in this work for absorbing spheres is comparable to previous reported measurements. For both absorbing and non-absorbing spheres, a statistical framework is developed for including the contributions to random error due to CPC measurement uncertainty, R L , statistical fluctuations in

Gas chromatographic peaks were demonstrated to have the form of normal distribution curves. A mathematical treatment has been developed which permits the calculation of the areas of these curves from the statistical parameters, height of the mode (peak height), and standard deviation u. The standard deviation equals the width of the peak a t 0.882 of peak height. Methods given for the evaluation of the mutual effects of overlapping peaks have made it possible t o obtain corrected peak heights. The standard deviation of the gas chromatography peak has been found to vary linearly with the retention time, thus permitting the graphical estimation of u for use with corrected peak heights in the calculation of true areas for overlapping peaks. The method has also been extended to the treatment of skewed, overlapping pealts. The variation of u with retention time, its constancy, and its relationship t o the number of theoretical plates are discussed. INTRODUCTIONIn quantitative gas chron~atography using a differential detector, the area under the peak corresponding to a colnpound is proportioilal to the aiuount of that compound present in tlie gas stream. Area measurements are therefore fundamental.Various procedures have been proposed for the measurement of peak areas. The integrator built into the recorder is the least laborious, but suffers from obvious disadvantages if there is a base-line drift or if there are overlapping peaks. The triangulation procedure (1) gives a good first approximation. Another procedure which has been widely used is to cut out the pealrs or a tracing of the pealts, and to weigh the cut paper. Planimeter tracing has also been used. With all these procedures, precision and accuracy suffer when the peaks are very narroxv or if two or more peaks have a moderate overlap. AREA OF SYiLIMETRICAL PE-AKS ( a ) Isolated PeaksI t has been pointed out and developed theoretically (2, 3, 4) that the peaks obtained with a well-designed chromatograph closely approxiinate a nornlal or Gaussian distribution curve as ~1 1 0~~1 1 in Fig. 1. The equatioii for this type of curve is given by Goulden (5) as where Y is the height of tlie curve measured a t a distance x from tlie mean, i V is the number of variates, which, for our purposes may be tal

We describe here the construction and characterization of a new combustion-chamber system (the NCAT chamber) for studying the optical and physicochemical properties of biomass burning (BB) aerosols. This system is composed of a ~9 m 3 fluorinated ethylene propylene (FEP) film reactor placed in a temperature-controlled room that uses a tube furnace to combust biomass fuel samples under controlled conditions. The optical properties are measured using a cavity ringdown spectrometer and nephelometer. Aerosol number density and size classification used condensation particle counter, and differential mobility analyzer. Other analytical instruments, used include NO x , O 3 , CO, and CO 2 analyzers, a gas chromatograph, and particle filter samples for determining the physicochemical and morphological properties. The construction details and characterization experiments are described, including measurements of the BB particulate size distribution and deposition rate, gas wall loss rates, dilution rate, light intensity, mixing speed, temperature and humidity variations, and air purification method. The wall loss rates for NO, NO 2 , and O 3 were found to be (7.40 ± 0.01) × 10 -4 , (3.47 ± 0.01) × 10 -4 , and (5.90 ± 0.08) × 10 -4 min -1 , respectively. The NO 2 photolysis rate constant was 0.165 ± 0.005 min -1 , which corresponds to a flux of (7.72 ± 0.25) × 10 17 photons nm cm -2 s -1 for 296.0-516.8 nm, and the particle deposition rate was (9.46 ± 0.18) × 10 -3 min -1 for 100 nm mobility diameter BB particles from pine. Preliminary results of the single scattering albedo of fresh and aged BB aerosols are also reported.

Abstract:The refractive index (RI) is an important parameter in describing the radiative impacts of aerosols. It is important to constrain the RI of aerosol components, since there is still significant uncertainty regarding the RI of biomass burning aerosols. Experimentally measured extinction cross-sections, scattering cross-sections, and single scattering albedos for white pine biomass burning (BB) aerosols under two different burning and sampling conditions were modeled using T-matrix theory. The refractive indices were extracted from these calculations. Experimental measurements were conducted using a cavity ring-down spectrometer to measure the extinction, and a nephelometer to measure the scattering of size-selected aerosols. BB aerosols were obtained by burning white pine using (1) an open fire in a burn drum, where the aerosols were collected in distilled water using an impinger, and then re-aerosolized after several days, and (2) a tube furnace to directly introduce the BB aerosols into an indoor smog chamber, where BB aerosols were then sampled directly. In both cases, filter samples were also collected, and electron microscopy images were used to obtain the morphology and size information used in the T-matrix calculations. The effective radius of the particles collected on filter media from the open fire was approximately 245 nm, whereas it was approximately 76 nm for particles from the tube furnace burns. For samples collected in distilled water, the real part of the RI increased with increasing particle size, and the imaginary part decreased. The imaginary part of the RI was also significantly larger than the reported values for fresh BB aerosol samples. For the particles generated in the tube furnace, the real part of the RI decreased with particle size, and the imaginary part was much smaller and nearly constant. The RI is sensitive to particle size and sampling method, but there was no wavelength dependence over the range considered (500-680 nm). Our values for the RI of fresh (white pine) biomass burning aerosols ranged from 1.33 + i0.008 to 1.74 + i0.008 for 200-nm, 300-nm, and 400-nm diameter particles. These are within the range of RI values in the most recent study conducted during the Fire Laboratory at Missoula Experiments (FLAME I and II), which were 1.55 to 1.80 for the real part, and 0.01-0.50 for the imaginary part, for fresh BB aerosols with diameters of 200-570 nm. There is no clear trend on the dependence of the RI values on particle size. The RI values derived from measurements of aerosols produced from the combustion of hydrocarbons and diesel cannot be used for BB aerosols.

Abstract. An accurate measurement of the optical properties of aerosol is critical for quantifying the effect of aerosol on climate. Uncertainties persist and results of measurements vary significantly. Biomass burning (BB) aerosol has been extensively studied through both field and laboratory environments for North American fuels to understand the changes in optical and chemical properties as a function of aging. There is a need for a wider sampling of fuels from different regions of the world for laboratory studies. This work represents the first such study of the optical and chemical properties of wood fuel samples commonly used for domestic purposes in east Africa. In general, combustion temperature or modified combustion efficiency (MCE) plays a major role in the optical properties of the emitted aerosol. For fuels combusted with MCE of 0.974±0.015, which is referred to as flaming-dominated combustion, the single-scattering albedo (SSA) values were in the range of 0.287 to 0.439, while for fuels combusted with MCE of 0.878±0.008, which is referred to as smoldering-dominated combustion, the SSA values were in the range of 0.66 to 0.769. There is a clear but very small dependence of SSA on fuel type. A significant increase in the scattering and extinction cross section (with no significant change in absorption cross section) was observed, indicating the occurrence of chemistry, even during dark aging for smoldering-dominated combustion. This fact cannot be explained by heterogeneous oxidation in the particle phase, and we hypothesize that secondary organic aerosol formation is potentially happening during dark aging. After 12 h of photochemical aging, BB aerosol becomes highly scattering with SSA values above 0.9, which can be attributed to oxidation in the chamber. Aging studies of aerosol from flaming-dominated combustion were inconclusive due to the very low aerosol number concentration. We also attempted to simulate polluted urban environments by injecting volatile organic compounds (VOCs) and BB aerosol into the chamber, but no distinct difference was observed when compared to photochemical aging in the absence of VOCs.