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Atmospheric Science Papers (Blue Books)

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https://hdl.handle.net/10217/100334
Much of this digital collection of Blue Books comes from CSU's Department of Atmospheric Science. Included are student theses and dissertations and project reports dating from 1959 to 2007. The works focus on different areas of atmospheric science research such as climate change, severe weather, climatology, solar radiation, remote sensing, wind forecasting, and air quality.

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Browsing Atmospheric Science Papers (Blue Books) by Subject "Aerosols -- Measurement"

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    Aerosol black carbon measurements in Fort Collins, Colorado
    (Colorado State University. Libraries, 1999-03) Calame, Lorraine, author; Collett, Jeffrey L., Jr., author
    Aerosol black carbon concentrations were measured in Fort Collins, a small city in northern Colorado. A Magee Scientific aethalometer was used to obtain real time data. In 1997 a gradual build-up in monthly BC concentrations over the late spring and summer was observed to peak in August and then decline. The number of days featuring high concentrations (> 2000 ng/m3 for 30 minutes) was also observed to rise and fall with an August peak. The monthly trends in aerosol black carbon concentrations suggest some seasonality. Observations of aerosol black carbon concentrations made during this study reveal monthly mean concentrations that vary from 487 to 1004 ng/m3. The BC concentration timelines showed there are usually two daily peaks in the data. These peaks usually occur between 0600 - 0800 and 1600 - 2100, hours associated with peak traffic. Concentrations of BC were found to correlate reasonably well with CO concentrations over time scales of up to a week. The covariance in our data set suggests they were emitted from a common set of combustion sources. The results of this study indicate there is little relationship between measured BC concentrations and long range transport patterns, as back-trajectory results indicated that long range transport of air masses from particular regions does not influence whether BC concentrations in Ft. Collins are high or low. The observed BC concentrations tended to decrease with increasing wind speed which is consistent with emissions from a local source that would tend to be diluted at higher wind speeds. On shorter timescales of minutes to hours, the study revealed the importance of individual sources on BC concentrations. Passages of diesel locomotives near the site were shown to increase BC concentrations on many occasions when local winds were favorable to transporting locomotive emissions to the aerosol sample site. The impact of this source, however, was fairly limited in its duration, with concentration spikes typically lasting only about 10 minutes. Train passage also exerted an indirect effect on BC concentrations, perhaps associated with a period of increased BC emissions by vehicles idled at train crossings. Fires were also shown to influence BC concentrations during the study. The large fires associated with the July 1997 flood and smaller fires associated with a CSU student riot were observed to increase BC concentrations. The number of fires during the study period, however, was very low. Impacts of two prescribed bums along the Front Range on Ft. Collins BC concentrations were observed to be fairly minor. Correlation of BC concentrations with "total" particle number concentrations (as measured by a Condensation Nucleus Counter), and number concentrations of particles with diameters greater than 0.3 µm (as measured by a Climet Optical Particle Counter) were extremely weak on long time scales and often weak on time scales as short as a day. This reflected the diverse sources of the aerosols. Some of these were probably primary combustion aerosol (and therefore are likely to correlate with BC), but others were the secondary aerosol fraction of CN or particles larger than 0.3 µm that are not expected to correlate strongly with BC concentrations. BC concentrations were independent of the diurnal pressure patterns, but were affected by synoptic pressure patterns. Frontal passages were marked by low BC concentrations. BC concentrations were not found to be depressed on summer days featuring precipitation, as the duration of summer thunderstorms is typically too short to scavenge enough aerosol particles to significantly influence the daily average BC concentration. In addition, primary aerosol particles that are generated locally by vehicle emissions would be replenished rapidly in the atmosphere following precipitation. Absorption coefficients were derived from the aethalometer and the difference between transmissometer and nephelometer data. The monthly mean values ranged from 0.005 - 0.009 km-' for the aethalometer, and 0.036 - 0.038 km-1 for the transmissometer and nephelometer. The aethalometer derived absorption coefficients are on the order of 10 - 20% of the absorption coefficients determined from the paired nephelometer and transmissometer measurements, and only 6 - 11% of the total extinction measured by the transmissometer.
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    Effects of clouds on aerosol and chemical species processing, production, and distribution in the boundary layer and upper troposphere
    (Colorado State University. Libraries, 1998-09) Zhang, Yiping, author
    Clouds play important roles in boundary layer and tropospheric aerosol and chemical processes. This work addresses the aerosol and chemical species processing, production, and distribution through two important types of clouds: convective and stratocumulus clouds. A modeling study of the effects of convection on the transformation and redistribution of chemical species and evolution and redistribution of aerosol particles in the troposphere is presented. A two-mode, two-moment aerosol evolution model is coupled with a two­ dimensional, mixed-phase, two-moment microphysics, Eulerian cloud model and a sulfate cloud chemistry model [Kreidenweis et al., 1997; Taylor et al., 1997; Zhang et al., 1998] to examine the new particle formation mechanism and the importance of different pathways for aqueous sulfate production. In the simulations, the complexation of CH20 with S(IV) is found to be of minor importance in most of the model cloud, compared with the oxidation of S(IV) by H202 and 03, while Fe (III)-catalyzed oxidation plays an important role in aqueous sulfate production. Significant S02 is convectively transported to the mid-to­ upper troposphere, where it is oxidized to gas-phase H2S04. After cloud processing, cloud condensation nuclei (CCN) particles are removed by precipitation and graupel to form a CCN-depleted region above cloud top and in the cold and humidified cloud outflow region. The new particle formation in the mid- to upper- troposphere interacts with cloud processing and transport of chemical species and aerosol particles and produces a peak of small particle concentration in the outflow region. The model results suggest that both small aerosols and aerosol precursors can be transported into the mid- to upper- troposphere by convective clouds, affecting vertical profiles of aerosol concentrations. The sensitivity of the S(VI) and aerosol production, S02 and aerosol redistribution to variations in the initial chemical and aerosol conditions and several model parameters are also examined. A trajectory ensemble model (TEM) is used to investigate stratocumulus processing of gases and C CN in the boundary layer. The fully coupled aqueous chemistry/ cloud microphysics model (Feingold et al., 1998; Zhang et al., 1998] is driven by a set of boundary layer parcel trajectories derived from a large eddy simulation model to study the effects of variations in the initial chemical fields and initial aerosol number concentration on chemical heterogeneity, broadening of the CCN and drop spectra, effective drop radius, and differences in the overall fractional conversion between the TEM and a single parcel experiencing mean conditions in a stratocumulus-capped marine boundary layer. It is found that the TEM offers a more representative method of describing the stratocumulus processing of aerosol and gases than does a single parcel model. In the base case simulation, the 03 oxidation rate averaged over all parcels is larger than the H202 oxidation rate, whereas the volume-mean cloudwater pH might suggest that H202 oxidation dominates. The liquid water-weighted pH generally increases with increasing drop size, to a peak pH. The drop size at this peak corresponds to the minimum in S(VI) concentration and is located near the mode of the drop mass distribution. However, the pH dependence on drop size at larger cloud drop sizes is affected by the initial chemical conditions. Aqueous chemistry contributes to the broadening of the drop size distribution, but the magnitude of the broadening depends on the initial aerosol and chemical conditions. In cases where more mass is added onto large particles in the tail of the initial CCN spectrum, the broadening of the drop spectrum is most evident, and may even trigger the collision coalescence process and drizzle formation in stratocumulus clouds. The change in initial CCN number concentration has the most prominent effect on the effective drop radius.
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    Predicting particle critical supersaturation from hygroscopic growth measurements in the humified tandem differential mobility analyzer
    (Colorado State University. Libraries, 1998-09-25) Brechtel, Fredrick J., author
    A new method is described to estimate the critical supersaturation of a quas1- monodisperse, dry particle population composed of pure salts using measurements of hygroscopic growth at several relative humidities below 100%. We describe how Kohler theory may be used to derive two chemical composition dependent parameters, with appropriate accounting for solution effects through a simplified model of the osmotic coefficient. Using a regression routine, the two unknown chemical parameters are derived by fitting the Kohler model to the results from hygroscopic growth experiments. The derived parameters are then used in the Kohler model to calculate critical supersaturations for given dry particle size. From these studies, it is possible to derive the cloud condensation nucleus spectrum if simultaneous measurements of the total number size distribution are made and a sufficient number of critical supersaturations for different particle sizes are determined to characterize the cloud condensation nucleus sub-population of the total particle population. This work represents one of the first, detailed studies on the relationships between particle hygroscopicity and CCN activity using simultaneous measurements of droplet growth and particle critical supersaturation on particles composed of pure salts. In this work we present the theory and methodology that allow the critical supersaturation to be derived from hygroscopic growth measurements, and perform numerical sensitivity studies with respect to assumptions made and anticipated uncertainties in key input parameters to the Kohler model. Laboratory studies are conducted on particles composed of NaCl, (NH4 )2SO 4 , NH4 HSO4 , internally and externally mixed N aC1-(NH4 ) 2SO4 to validate the technique. Studies on ambient particles are also conducted to test if the technique can predict accurate values of Scrit for particles of unknown chemical composition. Results from numerical studies show that for particle diameters of 40 and 100 nm, the maximum errors in critical supersaturations derived using the proposed method are between ±15%. This error is similar to the observed average experimental uncertainty in estimates of the critical supersaturation of -0.6%±11 % determined from CCN studies on particles of known composition. Laboratory studies demonstrate that the critical supersaturation can be derived from hygroscopic growth measurements within experimental uncertainties for the particles of known chemical composition examined in this work. The largest observed differences (-3% to -62%) between HTDMA and CCN derived values of Scrit occurred for ambient particle samples where the chemical composition was unknown and most likely contained a significant amount of hydrophobic material. The numerical and laboratory studies indicate that the proposed technique can establish quantitative relationships between particle size and hygroscopic growth and cloud condensation nucleus activity. The method should help reduce uncertainties in estimates of the indirect effect of particles on climate by allowing more commonly measured aerosol properties, for example particle size and hygroscopic growth, to be directly related to the particle critical supersaturation.