[1] Recent decreases in nitrogen oxide (NO x = NO + NO 2 ) emissions from eastern U.S. power plants and their effects on regional ozone are studied. Using the EPA 1999 National Emission Inventory as a reference emission data set, NO x and sulfur dioxide (SO 2 ) emission rates at selected power plants are updated to their summer 2003 levels using Continuous Emission Monitoring System (CEMS) measurements. The validity of the CEMS data is established by comparison to observations made on the NOAA WP-3 aircraft as part of the 2004 New England Air Quality Study. The impacts of power plant NO x emission decreases on O 3 are investigated using the WRF-Chem regional chemical forecast model. Summertime NO x emission rates decreased by approximately 50% between 1999 and 2003 at the subset of power plants studied. The impact of NO x emission reductions on ozone was moderate during summer 2004 because of relatively cool temperatures and frequent synoptic disturbances. Effects in individual plant plumes vary depending on the plant's NO x emission strength, the proximity of other NO x sources, and the availability of volatile organic compounds (VOCs) and sunlight. This study provides insight into the ozone changes that can be anticipated as power plant NO x emission reductions continue to be implemented throughout the United States.

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[1] This work describes measurements of the heterogeneous depositional nucleation of ice on micrometer-sized (NH 4 ) 2 SO 4 (AS), maleic acid (C 4 H 4 O 4 ) (MA), and mixed AS/MA particles and on thin NH 4 NO 3 (AN) films. The critical saturation ratio (S crit ) required for heterogeneous nucleation was found to be similar and temperature-dependent for all solids, ranging from S crit = 1.42 ± 0.04 at 190 K to S crit = 1.04 ± 0.05 at 240 K. Deliquescence of the solids was not observed in any experiment; ice nucleation always occurred below the deliquescence relative humidity. The observed saturation ratios for ice nucleation were all substantially lower than the saturation ratios required for homogeneous nucleation. These results suggest that vapor deposition of ice may compete with deliquescence for crystalline organic and inorganic solids below the eutectic temperature.

[1] We have constructed a pulsed cavity ring-down spectrometer (CARDS) for simultaneous measurements of nitrogen dioxide (NO 2 ), the nitrate radical (NO 3 ), and dinitrogen pentoxide (N 2 O 5 ) in the atmosphere. In this paper, we describe the development of the instrument to measure NO 2 via its absorption at 532 nm. The NO 2 detection channel was calibrated against a NIST traceable calibration standard as well as a photolysis-chemiluminescence (P-CL) NO 2 detector. The absorption cross section of NO 2 at 532 nm was determined to be (1.45 ± 0.06) Â 10 À19 cm 2 . The NO 2 detection limit (1s) for 1 s data is 40 pptv, and the instrument response is accurate within ±4% (1s) under laboratory conditions. The linear dynamic range of the instrument has been verified from the detection limit to above 200 ppbv (r 2 > 99.99%). For field measurements it is necessary to correct the CARDS NO 2 signal for absorption by ozone. Under ambient conditions we report 1 s NO 2 CARDS data with total uncertainty ±(4%, 60 pptv + 0.4 Â (pptv/ppbv) Â O 3 ) (1s). The instrument was deployed in the field during the New England Air Quality Study-International Transport and Chemical Transformation on board the NOAA research vessel Ronald H. Brown in the summer of 2004 and in Boulder, Colorado, in the winter of 2005. In both campaigns, CARDS and P-CL NO 2 measurements were highly correlated (r 2 > 98%), indicating the absence of interfering gas phase absorbers at 532 nm other than ozone and the suitability of CARDS to measure NO 2 in the troposphere.

We report comprehensive thermodynamic property measurements of 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone. The (p, ρ, T) behavior was measured from T = (225 to 470) K with pressures up to 36 MPa with a two-sinker densimeter. These measurements include compressed-liquid states and states in the extended critical region. The vapor-phase speed of sound was measured from T = (325 to 500) K with pressures up to 1.7 MPa with a spherical acoustic resonator. The vapor pressure was measured in the spherical resonator from T = (325 to 440) K with a static technique. The density and speed of sound of the liquid was measured from T = (278 to 308) K at atmospheric pressure (p = 83 kPa) in a benchtop instrument employing a vibrating-U-tube densimeter and a time-of-flight speed-of-sound technique. These data, together with selected data from the fluid manufacturer, have been used to develop an equation of state explicit in the Helmholtz energy covering the fluid region. The equation of state represents the present experimental vapor-pressure data with an RMS deviation of 0.066 %, the (p, ρ, T) data to 0.067 %, and the speed-of-sound data to 0.029 %. This fluid is of interest as the working fluid in Rankine-cycle power applications and as a fire extinguishing agent; it is also known by the trade names Novec-649 and Novec-1230.

Measurements of density, speed of sound, and viscosity have been carried out on liquid certified reference materials for biofuels as a function of temperature at ambient pressure. The samples included anhydrous and hydrated bioethanol and two biodiesel fuels from different feedstocks, soy and animal fat. The ethanol samples were measured from a maximum temperature of 60 to 5 °C (speed of sound) and to −10 °C (density and viscosity), respectively. The biodiesel samples were characterized from 100 °C (density and viscosity) and from 70 °C (speed of sound) to 10 °C (animal fat-based) and 5 °C (soy-based). Densities were measured with two vibrating-tube instruments of different accuracy. The speeds of sound were measured with a propagation-time method in an acoustic cell that was combined with one of the densimeters. Viscosities were measured with an open gravitational capillary viscometer and with a rotating concentric cylinder viscometer, according to Stabinger. The measurement results are reported with detailed uncertainty analyses.

[1] Bromine oxide (BrO) was measured in situ during the Arctic Tropospheric Ozone Chemistry (ARCTOC) '96 campaign in Ny Å lesund, Spitsbergen (April-May 1996), and during the Alert 2000 Polar Sunrise Experiment in Alert, Nunavut, Canada (April-May 2000). Measurements were made in near-surface air during low-ozone events in early May at both sites. The average of the in situ concentrations of BrO at Ny Å lesund is consistent with the path average of near-simultaneous long-path differential optical absorption spectroscopy measurements, but there is considerable scatter in a point-by-point comparison. The differences between these observations are consistent with a strong surface influence on reactive bromine. We see similar variability of the in situ measurements at Alert, which reflects the real variability of both surface sources and sinks. The fluctuations of BrO abundances are used to assess the expected loss rates and associated lifetimes of ozone during depletion events. We show that ozone loss will be underpredicted by any temporal or spatial average of BrO.

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