Aerosol particle light scattering at a perturbed mid-latitude continental northern hemisphere site and its dependence on relative humidity, wavelength of light, particle size and composition

Recent model predictions indicate that sulfate aerosol particles cause radiative forcing of the same magnitude but of opposite sign than the forcing caused by anthropogenic greenhouse gases. The spatial and temporal variability of parameters used in the models are highly uncertain resulting in uncertain model predictions of the aerosol radiative forcing. Such parameters related to aerosol particle properties and direct radiative forcing are: the hygroscopic growth factor (f(RH)), the upscatter fraction ($\beta$), and the mass scattering efficiency, ($\alpha$). These three parameters can be estimated from regional measurements of total light scattering and back-scattering coefficients as functions of relative humidity, particle composition and size, and wavelength of light.To take and validate such measurements: (i) an ambient aerosol monitoring station was designed and built for continuous ambient aerosol measurements, south of Bondville, in Central Illinois, U.S.A., (ii) instrumentation that measures aerosol particle light scattering coefficients under controlled relative humidity conditions was designed, built, calibrated and tested, (iii) a model was developed that estimates hygroscopic particle growth under the assumption of thermodynamic equilibrium and for metastable particles, (iv) experiments with laboratory generated aerosol particles were completed to calibrate the instrumentation and test the models, and (v) tests for closure were completed using the experimental and modeled results.Examination of the measurements to date, showed that about 95% of the aerosol gravimetric mass (dp $\le$ 1 $\mu$m), at Bondville, that is identifiable with ion chromatography consists of NH\sb4\sp+ and SO\sb4\sp{2-}. Mean values and standard deviations for f(RH) were in the range 1.1 $\pm$ 0.4 to 2.3 $\pm$ 1.1 depending on wavelength and direction of scattering. Mean values and standard deviations for b were in the range 7.0% $\pm$ 1.4% to 21.7% $\pm$ 4.18% depending on relative humidity and wavelength. \rm\alpha\sb{so\sbsp{4}{2-}} (estimated with multiple linear regression) was 8.25 m\sp2/g.A model, was developed to test closure. The model integrates results from thermodynamic equilibrium calculations and experimental data on metastable particles, with light scattering modeling. Tests for closure indicated that the water insoluble component of the aerosol, which is not accounted for by ion chromatography, can be very important in modifying the optical properties of the aerosol.U of I OnlyETDs are only available to UIUC Users without author permissio

Modeling Ammonia Emissions Post Chemical Fertilizer Application

We present alternative methods for estimating spatial surrogates and temporal factors for ammonia (NH3) emissions from chemical fertilizer usage (CFU), in the USA, at spatial and temporal scales used to simulate regional air quality and deposition of reactive nitrogen to ecosystems. The newly developed Improved Spatial Surrogate (ISS) method incorporates year-specific fertilizer sales data, high resolution and year-specific crop maps, and local crop nitrogen demands to allocate NH3 emissions at 4km× 4 km grid cells. Results are compared with the commonly used gridded emission estimates by the Sparse Matrix Operator Kernel Emissions (SMOKE) preprocessor. NH3 emissions over Central Illinois in the USA, estimated at the 4 km× 4 km grid level in SMOKE and ISS methods, exhibit differences between 10% and 120%, with 58% of the grid cells exhibiting more than ±10% difference. Application of the ISS method for a larger domain over the Midwest USA, at 4km×4km, reflected similar differences. We also employed the Denitrification Decomposition (DNDC) model to develop daily temporal factors of NH3 emissions from CFU using multi-site and multi-year analyses. Ratio of temporal factors estimated by SMOKE and DNDC methods is 0.54 ± 2.35, with DNDC identifying daily emission peaks 2.5–8 times greater than SMOKE. Identified emission peaks will be useful for future air quality modeling efforts to understand particulate matter episodes, as well as trends in regional particulate matter formation and nitrogen deposition for Midwest USA, using the proposed NH3 emissions inventory.NSF Award No. AGS 12-36814 with accompanying research experience for undergraduates (REU)University of Illinois Campus Research Boar

Open burning and open detonation PM₁₀ mass emission factor measurements with optical remote sensing

<div><p>Emission factors (EFs) of particulate matter with aerodynamic diameter ≤10 µm (PM₁₀) from the open burning/open detonation (OB/OD) of energetic materials were measured using a hybrid-optical remote sensing (hybrid-ORS) method. This method is based on the measurement of range-resolved PM backscattering values with a micropulse light detection and ranging (LIDAR; MPL) device. Field measurements were completed during March 2010 at Tooele Army Depot, Utah, which is an arid continental site. PM₁₀ EFs were quantified for OB of M1 propellant and OD of 2,4,6-trinitrotoluene (TNT). EFs from this study are compared with previous OB/OD measurements reported in the literature that have been determined with point measurements either in enclosed or ambient environments, and with concurrent airborne point measurements. PM₁₀ mass EFs, determined with the hybrid-ORS method, were 7.8 × 10⁻³ kg PM₁₀/kg M1 from OB of M1 propellant, and 0.20 kg PM₁₀/kg TNT from OD of TNT. Compared with previous results reported in the literature, the hybrid-ORS method EFs were 13% larger for OB and 174% larger for OD. Compared with the concurrent airborne measurements, EF values from the hybrid-ORS method were 37% larger for OB and 54% larger for OD. For TNT, no statistically significant differences were observed for the EFs measured during the detonation of 22.7 and 45.4 kg of TNT, supporting that the total amount of detonated mass in this mass range does not have an effect on the EFs for OD of TNT.</p> <p></p><p>Implications:</p><p> <i>Particulate matter (PM) in the atmosphere affects the health of humans and ecosystems, visibility, and climate. Fugitive PM emissions are not well characterized because of spatial and temporal ubiquity and heterogeneity. The hybrid-ORS method is appropriate for quantifying fugitive PM emission factors (EFs) because it captures the spatial and temporal dispersion of ground level and elevated plumes in real time, without requiring numerous point measurement devices. The method can be applied to provide an opportunity to reduce the uncertainty of fugitive PM EFs and readily update PM emissions in National Emission Inventories for a range of fugitive PM sources.</i></p> <p></p></div