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A new instrument for monitoring atmospheric C[O.sub.2] has been developed based on the measurement of the speed of sound in air. The instrument uses a selective scrubber to yield highly precise and accurate measurements of C[O.sub.2] mixing ratios at ambient concentrations. The instrument has a precision of 0.3 ppmv (1[sigma]) with a signal that is independent of pressure and requires a flow rate of only 30 mL/min. Laboratory measurements of atmospheric C[O.sub.2] showed excellent agreement with values obtained by nondispersive infrared absorption. The instrument has the advantage of collecting continuous, high-precision data every 25 s and can be modified for vertical profiling studies using kites, balloons, or light aircraft for the purpose of measuring landscape-scale fluxes. 10.1021/ac101365p

A new portable instrument has been developed that offers rapid detection of ozone at the parts per billion (ppb) level for personal exposure monitoring. The personal ozone monitor is based on the EPA Federal Reference Method of UV absorbance and has the advantage of being small (10 cm x 7.6 cm x 3.8 cm), lightweight (0.3 kg), low power (2.9 W), and battery-operated. The instrument can be worn by an individual during normal daily activities because it is unaffected by humidity, physical orientation, temperature, and vibration. In order to eliminate any significant interference from water vapor, Nation tubing was installed before the detection cell, and the optical path was lined with quartz. A precision of 1.5 parts per billion by volume (ppbv) and limit of detection of 4.5 ppbv (S/N = 3) was demonstrated with the instrument making measurements every 10 s. 10.1021/ac1013578

A highly portable calibration source of nitric oxide (NO) based on photolysis of nitrous oxide (N2O) supplied by 8- or 16-g disposable cartridges is demonstrated to serve as an accurate and reliable transfer standard for the calibration of NO monitors in the field. The instrument provides output mixing ratios in the range 0-1,000 ppb with a precision and accuracy of better than the greater of 3 ppb or 3% of the target NO mixing ratio over a wide range of environmental conditions of ambient temperature (8.5-35.0 °C), pressure (745-1,015 mbar corresponding to 2.7-0.0 km elevation) and relative humidity (0-100% RH). Combination of the NO calibration source with a previously described ozone calibration source based on photolysis of oxygen in air provides a new instrument capable of outputting calibrated mixing ratios of NO, ozone (O3) and nitrogen dioxide (NO2), where the NO2 is produced by the stoichiometric gas-phase reaction of NO with O3. The portable NO2/NO/O3 calibration source requires no external gas cylinders and can be used for calibrations of NO, NO2 and O3 instruments for mixing ratios up to 1,000, 500, and 1,000 ppb, respectively. This portable calibrator may serve as a convenient transfer standard for field calibrations of ozone and NOx air pollution monitors. [ABSTRACT FROM AUTHOR]

It was observed that silver colloids exhibit blinking, independent of the nature of the adsorbate in the presence or absence of surface enhanced Raman scattering (SERS). It is believed that further research of the relationship between optical behavior and SERS and the continuum will lead to better understanding of the entire process.

Understanding nitrogen oxides (NOx = NO + NO2) measurement techniques is important as air-quality standards become more stringent, important sources change, and instrumentation develops. NOx observations are compared in two environments: source testing from the combustion of Southwestern biomass fuels, and urban, ambient NOx. The latter occurred in the urban core of Albuquerque, NM, at an EPA NCORE site during February-March 2017, a relatively clean photochemical environment with ozone (O3) <60 ppb for all but 6 hr. We compare two techniques used to measure NOx in biomass smoke during biomass burning source testing: light absorption at 405 nm and a traditional chemiluminescence monitor. Two additional oxides of nitrogen techniques were added in urban measurements: a cavity attenuated phase shift instrument for direct NO2, and the NOy chemiluminescence instrument (conversion of NOy to NO by molybdenum catalyst). We find agreement similar to laboratory standards for NOx, NO2, and NO comparing all four instruments (R2 > 0.97, slopes between 0.95 and 1.01, intercepts < 2 ppb for 1-hr averages) in the slowly varying ambient setting. Little evidence for significant interferences in NO2 measurements was observed in comparing techniques in late-winter urban Albuquerque. This was also confirmed by negligible NOz contributions as measured with an NOy instrument. For the rapidly varying (1-min) higher NOx concentrations in biomass smoke source testing, larger variability characterized chemiluminescence and absorption instruments. Differences between the two instruments were both positive and negative and occurred for total NOx, NO, and NO2. Nonetheless, integrating the NOx signals over an entire burn experiment and comparing 95 combustion experiments, showed little evidence for large systematic influences of possible interfering species biasing the methods. For concentrations of <2 ppm, a comparison of burn integrated NOx, NO2, and NO yielded slopes of 0.94 to 0.96, R2 of 0.83 to 0.93, and intercepts of 8 to 25 ppb. We attribute the latter, at least in part, to significant noise particularly at low NOx concentrations, resulting from short averaging times during highly dynamic lab burns. Discrepancies between instruments as indicated by the intercepts urge caution with oxides of nitrogen measurements at concentrations <50 ppb for rapidly changing conditions. Implications: Multiple NOx measurement methods were employed to measure NOx concentrations at an EPA NCORE site in Albuquerque, NM, and in smoke produced by the combustion of Southwestern biomass fuels. Agreement shown during intercomparison of these NOx techniques indicated little evidence of significant interfering species biasing the methods in these two environments. Instrument agreement is important to understand for accurately characterizing ambient NOx conditions in a range of environments. [ABSTRACT FROM AUTHOR]

We describe and characterize a modular folded tubular photometer for making direct measurements of the concentrations of nitrogen dioxide (NO2) and specify how this method could be extended to measure other pollutants such as sulfur dioxide (SO2), ozone (O3), and black carbon particulate matter. Direct absorbance measurements using this photometer can be made across the spectral range from the ultraviolet (UV) to the near infrared. The absorbance cell makes use of modular components (tubular detection cells and mirror cubes) that allow construction of path lengths of up to 2m or more while maintaining low cell volumes. The long path lengths and low cell volumes enable sensitive detection of ambient air pollutants down to low part-perbillion levels for gas species and aerosol extinctions down to 1Mm-1, corresponding to ~0.1 μgm-3 for black carbon particulates. Pressure equalization throughout the stages of the absorbance measurement is shown to be critical to accurate measurements of analyte concentrations. The present paper describes the application of this photometer to direct measurements of nitrogen dioxide (NO2) and the incorporation of design features that also enable measurement of nitric oxide (NO) in the same instrument. Excellent agreement for ambient measurements along an urban roadside was found for both NO2 and NO measured by the folded tubular photometer compared to existing standard techniques. Compared to commonly used methods for measurements of NOx species, the advantages of this approach include (1) an absolute quantification for NO2 based on the Beer-Lambert law, thereby greatly reducing the frequency at which calibrations are required; (2) the direct measurement of NO2 concentration without prior conversion to NO as is required for the commonly used chemiluminescence method; (3) the use of modular components that allow construction of absorbance detection cells of varying lengths for extending the dynamic range of concentrations that can be measured; (4) a more economical instrument than other currently available direct measurement techniques for NO2; and (5) the potential for simultaneous detection of additional species such as SO2, O3, and black carbon in the same instrument. In contrast to other commercially available direct NO2 measurements, such as cavity-attenuated phase-shift spectroscopy (CAPS), the folded tubular photometer also measures NO simultaneously in the same apparatus by quantitatively converting NO to NO2 with ozone, which is then detected by direct absorbance. [ABSTRACT FROM AUTHOR]

The effects of four rates of phosphorus (P) fertilization (0, 0.56, 5.6 and 56.0 mg l−1) in soilless medium on the growth and physiology of mahogany seedlings were examined. The greatest response occurred at the 56 mg l−1 rate, with relatively small differences between other treatments. Biometric parameters increased at the 56 mg l−1 compared to 0 mg l−1 rate except root dry mass. Both the concentration and the total content of P and Kjeldahl nitrogen (N) increased in leaves, stems and roots with P application rate. Foliar concentrations of potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn) and sulfur (S) declined, and boron (B) and copper (Cu) increased with P limitations; zinc (Zn) and iron (Fe) were unaffected. Physiological adaptations of mahogany to P limitations include the preferential allocation of carbon (C) to plant roots, and increases in P utilization efficiency, P acquisition efficiency and the concentration of organic acids in xylem fluid. Root phosphatase activity was not influenced by P fertilization. [ABSTRACT FROM AUTHOR]