A new technique for obtaining aerosol size distributions with applications to estimates of aerosol properties (Texas)

The B&barbelow;ig B&barbelow;end R&barbelow;egional A&barbelow;erosol V&barbelow;isibility and O&barbelow;bservation study (BRAVO) was conducted from July to October 1999. The park is located in a remote region of southwest Texas on the border with Mexico but still has some of the poorest visibility of any Class 1 monitored area in the western United States. The park is frequently influenced by air masses carrying pollutants from Mexico and eastern Texas. Continuous physical, optical and chemical aerosol measurements were performed in an effort to understand the sources and contributions to haze in the park.; Dry aerosol size distributions were measured over the size range of 0.05 < D_p < 20 μm. Three instruments were used to cover this range, each having a different measurement technique. A new method was developed to align the size distributions in the instrument overlap regions, allowing for the retrieval of aerosol real refractive index and effective density, as well as size parameters for accumulation and coarse modes. The combined size distributions were used to calculate particle light scattering coefficients for the total distributions as well as investigate the fractional contribution of accumulation and coarse mode particles to total scattering coefficients.; Measurements of aerosol chemical composition were performed on a daily basis and demonstrated that the aerosol ionic composition was generally acidic with sulfate and ammonium as the dominant species, although organic and soil fractional contributions were significant episodically. Retrieved refractive index and effective density were compared with volume weighted model estimates based on measured fine and coarse chemical compositions and good agreement was found, well within experimental uncertainties.; Finally, surface-based measurements of aerosol properties were related to column measurements of aerosol optical depth at a USDA UVB radiometer network site located in the park. Correlations were observed between column-based measurements and in-situ measurements for the duration of the study. Angstrom wavelength exponents were calculated for surface-based and column-based aerosol optical depths over the wavelength range of 415–860 nm. Good agreement was observed between the methods, with variations in Angstrom exponents corresponding to changing aerosol properties.