The Ames airborne tracking sunphotometer was operated at the National Oceanic and Atmospheric Administration (NOAA) Mauna Loa Observatory (MLO) in 1991 and 1992 along with the NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) automated tracking sunphotometer and lidar. June 1991 measurements provided calibrations, optical‐depth spectra, and intercomparisons under relatively clean conditions; later measurements provided spectra and comparisons for the Pinatubo cloud plus calibration checks. June 1991 results are similar to previous MLO springtime measurements, with midvisible particle optical depth τp(λ = 0.526μm) at the near‐background level of 0.012 ± 0.006 and no significant wavelength dependence in the measured range (λ = 0.38 to 1.06μm). The arrival of the Pinatubo cloud in July 1991 increased midvisible particle optical depth by more than an order of magnitude and changed the spectral shape of τp(λ) to an approximate power law with an exponent of about −1.4. By early September 1991, the spectrum was broadly peaked near 0.5 μm, and by July 1992, it was peaked near 0.8 μm. Our optical‐depth spectra include corrections for diffuse light which increase postvolcanic midvisible τp values by 1 to 3% (i.e., 0.0015 to 0.0023). NOAA‐ and Ames Research Center (ARC)‐measured spectra are in good agreement. Columnar size distributions inverted from the spectra show that the initial (July 1991) post‐Pinatubo cloud was relatively rich in small particles (r<0.25μm), which were progressively depleted in the August‐September 1991 and July 1992 periods. Conversely, both of the later periods had more of the optically efficient medium‐sized particles (0.25

In this article we present results from a 2-year comprehensive exposure assessment study that examined the particulate matter (PM) exposures and health effects in 108 individuals with and without chronic obstructive pulmonary disease (COPD), coronary heart disease (CHD), and asthma. The average personal exposures to PM with aerodynamic diameters < 2.5 µm (PM 2.5 ) were similar to the average outdoor PM 2.5 concentrations but significantly higher than the average indoor concentrations. Personal PM 2.5 exposures in our study groups were lower than those reported in other panel studies of susceptible populations. Indoor and outdoor PM 2.5 , PM 10 (PM with aerodynamic diameters < 10 µm), and the ratio of PM 2.5 to PM 10 were significantly higher during the heating season. The increase in outdoor PM 10 in winter was primarily due to an increase in the PM 2.5 fraction. A similar seasonal variation was found for personal PM 2.5 . The high-risk subjects in our study engaged in an equal amount of dust-generating activities compared with the healthy elderly subjects. The children in the study experienced the highest indoor PM 2.5 and PM 10 concentrations. Personal PM 2.5 exposures varied by study group, with elderly healthy and CHD subjects having the lowest exposures and asthmatic children having the highest exposures. Within study groups, the PM 2.5 exposure varied depending on residence because of different particle infiltration efficiencies. Although we found a wide range of longitudinal correlations between central-site and personal PM 2.5 measurements, the longitudinal r is closely related to the particle infiltration efficiency. PM 2.5 exposures among the COPD and CHD subjects can be predicted with relatively good power with a microenvironmental model composed of three microenvironments. The prediction power is the lowest for the asthmatic children.

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[1] Desert dust and marine aerosols are receiving increased scientific attention because of their prevalence on intercontinental scales and their potentially large effects on Earth radiation, climate, other aerosols, clouds, and precipitation. The relatively large size of dust and marine aerosol particles produces scattering phase functions that are strongly forward peaked. Hence Sun photometry and pyrheliometry of these aerosols are more subject to diffuse light errors than is the case for smaller aerosols. We quantify these diffuse light effects for common Sun photometer and pyrheliometer fields of view (FOV), using data on dust and marine aerosols from (1) Aerosol Robotic Network (AERONET) measurements of sky radiance and solar beam transmission and (2) in situ measurements of aerosol layer size distribution and chemical composition. Accounting for particle nonsphericity is important when deriving dust size distribution from both AERONET and in situ aerodynamic measurements. We obtain correction factors that can be applied to Sun photometer or pyrheliometer results for aerosol optical depth (AOD) or direct beam transmission. The corrections are negligible (less than $1% of AOD) for Sun photometers with narrow FOV (half-angle h < $1°), but they can be as large as 10% of AOD at 354 nm wavelength for Sun photometers with h = 1.85°. For pyrheliometers (which can have h up to $2.8°), corrections can be as large as 16% at 354 nm. AOD correction factors are well correlated with AOD wavelength dependence (hence Å ngström exponent). We provide best fit equations for determining correction factors from Å ngström exponents of uncorrected AOD spectra, and we demonstrate their application to vertical profiles of multiwavelength AOD.

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