Abstract
Measurements of important reactive nitrogen species (NO, NO2, HNO3, PAN, PPN, NO3−, NOy), C1 to C6 hydrocarbons, O3, chemical tracers (C2Cl4, CO), and meteorological parameters were made in the troposphere (0 to 12 km) over the western Pacific (0°–50°N) during the Pacific Exploratory Mission‐West A campaign (September–October 1991). Under clean conditions, mixing ratios of NO, NO2, NOy, and O3 increased with altitude and showed a distinct latitudinal gradient. PAN showed a midtropospheric maximum, while nitric acid mixing ratios were generally highest near the surface. Measured NOy concentrations were significantly greater than the sum of individually measured nitrogen species (mainly NOx, PAN, and HNO3), suggesting that a large fraction of reactive nitrogen present in the atmosphere is made up of hitherto unknown species. This shortfall was larger in the tropics (≈65%) compared to midlatitudes (≈40%) and was minimal in air masses with high HNO3 mixing ratios (>100 ppt). A global three‐dimensional photochemical model has been used to compare observations with predictions and to assess the significance of major sources. It is possible that the tropical lightning source is much greater than commonly assumed, and both lightning source and its distribution remain a major area of uncertainty in the budgets of NOy and NOx. A large disagreement between measurement and theory exists in the atmospheric distribution of HNO3. It appears that surface‐based anthropogenic emissions provide nearly 65% of the global atmospheric NOy reservoir. Relatively constant NOx/NOy ratios imply that NOy and NOx are in chemical equilibrium and the NOy reservoir may be an important in situ source of atmospheric NOx. Data are interpreted to suggest that only about 20% of the upper tropospheric (7–12 km) NOx is directly attributable to its surface NOx source, and free tropospheric sources are dominant. In situ release of NOx from the NOy reservoir, lightning, direct transport of surface NOx, aircraft emissions, and small stratospheric input collectively maintain the NOx balance in the atmosphere. It is shown that atmospheric ratios of reactive nitrogen and sulfur species, along with trajectory analysis, can be used to pinpoint the source of Asian continental outflow. Compared to rural atmospheres over North America, air masses over the Pacific are highly efficient in net O3 production. Sources of tropospheric NOx cannot yet be accurately defined due to shortcomings in measurements and theory.
Highlights
The NASA Global TroposphericExperiment(GTE) consistsof a seriesof field programsdesignedto elucidatetheGif-sur-Yvette, France.Paper number 95JD01029. 0148-0227/96/95 JD- 01029505.00 compositionand chemistryof the Earth's global atmosphere [McNealetal., 1983].The Pacifictroposphereisa major region of the northern hemispherethat is relatively free of direct influencesfrom man-made pollution
The average,larger than thosecalculatedfrom NO assuming Table 1 providesa basic summaryof the meteorologythat photostationarystate conditions[Crawfordet al., this issue]. prevailedduring eachof the PacificExploratory Mission (PEM)-West A missions. One possibleinterpretationof this disagreementmay be that The data collectedover the westernPacificwere compared the measuredNO2 is too high due to possible with the output of a three-dimensionagl lobalphotochemical interferencefsromunknownNOv speciesA. possiblecandi- model (MOGUNTIA)
Data were further segregatedinto midlatitude/subtropica(4l 2ø-25øN)and tropical/equatoria(l25ø0øN) latitude bands.To eliminate short-termlocal influences and fresh pollution episodes,numerical filters(CO < 110ppbandNOy < 800 ppt)werealsoused whereappropriate.Basedon synopticmeteorology,missions6, 8, 9, and 10 were combinedto give a view of the midlatitude/ subtropica(l35øN) distributionws hilemissions15,18,and20 are used to describethe tropical/equatoriallatitude region ( 12øN).Backtrajectoriesshowedthat duringpreviousfiveor so days,these air masseswere only minimally impactedby fresh continental emissions
Summary
B., et al (1996), Reactive nitrogen and ozone over the western Pacific: Distribution, partitioning, and sources, J. This article is available at DigitalCommons@URI: https://digitalcommons.uri.edu/gsofacpubs/262.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.