Ground‐based measurements of NOx and total reactive oxidized nitrogen (NOy) at Sable Island, Nova Scotia, during the NARE 1993 summer intensive

Measurements of NO, NO2, and total reactive oxidized nitrogen (NOy) were added to ongoing measurements of aerosols, CO, and O3 at Sable Island (43°55′N, 60°01′W), Nova Scotia, during the North Atlantic Regional Experiment (NARE) 1993 summer intensive. Ambient levels of NOx and NOy were found to be highly variable, and elevated levels can be attributed to the transport of polluted continental air or presumably to relatively fresh emissions from sources upwind (e.g., ship traffic). The median values for NOx and NOy are 98 and 266 parts per trillion by volume (pptv), respectively. A multiday pollution episode occurred during which elevated NOx and NOy were observed with enhanced levels of O3, CO, and condensation nuclei. Air masses of recent tropical marine origin characterized by low and constant levels of O3 and CO were sampled after Hurricane Emily. The correlation between ozone and CO is reasonably good, although the relation is driven by the single pollution episode observed during the study. The correlation of O3 with NOy and with NOy‐NOx is complicated by the presumed NOy removal processes in the marine boundary layer. Examination of the radiosonde data and comparisons of the surface data with those obtained on the overflying aircraft provide clear indications of vertical stratification above the site

Photochemical production and loss rates of ozone at Sable Island, Nova Scotia during the North Atlantic Regional Experiment (NARE) 1993 summer intensive

Three weeks of summertime surface‐based chemical and meteorological observations at Sable Island, Nova Scotia during the North Atlantic Regional Experiment (NARE) 1993 summer intensive are used to study instantaneous photochemical production and loss rates of ozone by means of a numerical photochemical model. Results are most sensitive to the averaging scheme of data used to constrain the model and the ambient variability of the measurements. Model simulations driven by a time series of 5 min averaged data, most representative of the chemistry at the site, yield an average net photochemical ozone production of 3.6 ppbv/d. Estimates of net ozone production designed to filter out local sources, by using 1000–1400 LT median values of observations to drive the model and by excluding short‐lived hydrocarbons, give values ranging from 1 to 4 ppbv/d. These positive values of net ozone production within the marine boundary layer over Sable Island demonstrate the impact of polluted continental plumes on the background photochemistry of the region during the intensive. The dominant ambient variables controlling photochemical production and loss rates of ozone at the site during the measurement campaign appear to be levels of nitrogen oxides, ozone, nonmethane hydrocarbons, and solar intensity determined by cloud cover. The model partitioning of nitrogen oxides agrees for the most part with measurements, lending credence to calculated photochemical production and loss rates of ozone as well as inferred levels of peroxy radicals not measured at the site. Discrepancies, however, often occur during episodes of intermittent cloud cover, fog, and rain, suggesting the influence of cloud processes on air masses reaching the site

Measurements of atmospheric layers from the NASA DC-8 and P-3B aircraft during PEM-Tropics A

Tropospheric vertical structure was analyzed using in situ measurements of O₃, CO, CH₄, and H₂O taken on board the NASA DC-8 aircraft during three Pacific Exploratory Missions (PEMs): PEM-West A, September-October 1991 in the western Pacific; PEM-West B, February-March 1994 in the western Pacific; and PEM-Tropics A, September-October 1996 in the central and eastern Pacific. PEM-Tropics A added measurements from the NASA P3-B aircraft. We used a new mode-based method to define a background against which to find layers. Using only O₃ and H₂O, we found 472 layers in PEM-Tropics A (0.72 layers per vertical kilometer profiled), 237 layers in PEM-West A (0.54 layers/km), and 158 layers in PEM-West B (0.41 layers/km). Using all constituents, we found 187 layers in PEM-Tropics A (0.43 layers/km), 128 layers in PEM-West A (0.29 layers/km), and 80 layers in PEM-West B (0.21 layers/km). Stratospheric air, sometimes mixed with trapped pollution, was the dominant layer source in all three missions. The larger number of layers per kilometer in PEM-Tropics A was probably due to repeated profiling of several “superlayers” visible in many of the mission lidar and potential voracity profiles. The thickness of the superlayers was of order 1 km, and the horizontal extent was of order 1000 km. We found that layers have an important effect on the thermal structure. An example based on ozonesonde data from Tahiti is shown, where a dry, subsiding layer was stabilized by much greater radiative cooling at the base than at the top. The stabilized layer can trap pollution and force vertical plumes to spread into horizontal layers.United States. National Aeronautics and Space Administration (Grant NAG1-1758)United States. National Aeronautics and Space Administration (Grant NAG1-1901

An Assessment of HOx Chemistry in the Tropical Pacific Boundary Layer: Comparison of Model Simulations with Observations Recorded during PEM Tropics A

Reported are the results from a comparison of OH,H 2 O 2 CH 3 OOH, and O 3 observationswithmodel predictions based on current HO x –CH 4 reaction mechanisms. The field observations are thoserecorded during the NASA GTE field program, PEM-Tropics A. The major focus ofthis paper is on thosedata generated on the NASA P-3B aircraft during a mission flown in the marineboundary layer (MBL) nearChristmas Island, a site located in the central equatorial Pacific (i.e.,2° N, 157° W). Taking advantage of thestability of the southeastern trade-winds, an air parcel was sampled in aLagrangian mode over a significantfraction of a solar day. Analyses of these data revealed excellent agreementbetween model simulated andobserved OH. In addition, the model simulations reproduced the major featuresin the observed diurnalprofiles of H 2 O 2 and CH 3 OOH. In the case ofO 3 , the model captured the key observational feature whichinvolved an early morning maximum. An examination of the MBL HO x budget indicated that the O( 1 D) + H 2 Oreaction is the major source of HO x while the major sinks involveboth physical and chemical processes involving the peroxide species,H 2 O 2 and CH 3 OOH. Overall, the generally goodagreement between modeland observations suggests that our current understanding ofHO x –CH 4 chemistry in the tropical MBL isquite good; however, there remains a need to critically examine this chemistrywhen both CH 2 O and HO 2 are added to the species measured.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43056/1/10874_2004_Article_280634.pd

Ground-based measurements of NO x

Measurements of NO, NO2, and total reactive oxidized nitrogen (NOy) were added to ongoing measurements of aerosols, CO, and O3 at Sable Island (43°55′N, 60°01′W), Nova Scotia, during the North Atlantic Regional Experiment (NARE) 1993 summer intensive. Ambient levels of NOx and NOy were found to be highly variable, and elevated levels can be attributed to the transport of polluted continental air or presumably to relatively fresh emissions from sources upwind (e.g., ship traffic). The median values for NOx and NOy are 98 and 266 parts per trillion by volume (pptv), respectively. A multiday pollution episode occurred during which elevated NOx and NOy were observed with enhanced levels of O3, CO, and condensation nuclei. Air masses of recent tropical marine origin characterized by low and constant levels of O3 and CO were sampled after Hurricane Emily. The correlation between ozone and CO is reasonably good, although the relation is driven by the single pollution episode observed during the study. The correlation of O3 with NOy and with NOy-NOx is complicated by the presumed NOy removal processes in the marine boundary layer. Examination of the radiosonde data and comparisons of the surface data with those obtained on the overflying aircraft provide clear indications of vertical stratification above the site.Department of Civil and Environmental Engineerin