摘要:

Regional estimates of biogenic volatile organic compound (BVOC) emissions are important inputs for models of atmospheric chemistry and carbon budgets. Since forests are the primary emitters of BVOCs, it is important to develop reliable estimates of their areal coverage and BVOC emission rate. A new system is developed to estimate these emissions for specific tree genera at hourly and county level resolution. The U.S. Department of Agriculture, Forest Service Forest Inventory and Analysis Eastwide Database is used to describe the areal extent, species composition, and tree diameter distributions of United States forests. Horizontal canopy occupancy by genera is then estimated as a function of diameter at breast height. Growing season peak foliar masses are derived from the empirical literature for canopies of deciduous and coniferous genera. A simple canopy model is used to adjust photosynthetically active solar radiation at five vertical levels in the canopy. Leaf temperature and photosynthetically active radiation derived from ambient conditions above the forest canopy are then used to drive empirical equations to estimate genus level emission rates of BVOCs vertically through forest canopies. These genera level estimates are then aggregated to regional levels for comparison with the regulatory model currently used and for input into air quality models. The proposed model yields isoprene emission rate estimates for specific countries that are 5 to 10 times higher (and total BVOC emission rates that are 3 to 5 times higher) than the Environmental Protection Agency BVOC emission rate model currently used. Emission estimates of isoprene and monoterpenes from the new system compare favorably with rates measured at various forested sites in the United States.

ISSN:0148-0227    

DOI:10.1029/94JD00246

年代:1994

数据来源: WILEY

摘要:

During all eight flights conducted over the equatorial and tropical South Atlantic (27°–35°W, 2°N–11°S; September 9–22, 1989) in the course of the Chemical Instrumentation Test and Evaluation (CITE 3) experiment, we observed haze layers with elevated concentrations of aerosols, O3, CO, and other trace gases related to biomass burning emissions. They occurred at altitudes between 1000 and 5200 m and were usually only some 100–300 m thick. These layers extended horizontally over several 100 km and were marked by the presence of visible brownish haze. These layers strongly influenced the chemical characteristics of the atmosphere over this remote oceanic region. Air mass trajectories indicate that these layers originate in the biomass burning regions of Africa and South America and typically have aged at least 10 days since the time of emission. In the haze layers, O3and CO concentrations up to 90 and 210 ppb were observed, respectively. The two species were highly correlated. The ratio ΔO3/ΔCO (Δ, concentrations in plume minus background concentrations) is typically in the range 0.2–0.7, much higher than the ratios in the less aged plumes investigated previously in Amazonia. In most cases, aerosol (0.12–3 μm diameter) number concentrations were also elevated by up to 400 cm−3in the layers; aerosol enrichments were also strongly correlated with elevated CO levels. Clear correlations between CO and NOxenrichments were not apparent due to the age of the plumes, in which most NOxwould have already reacted away within 1–2 days. Only in some of the plumes could clear correlations between NOyand CO be identified; the absence of a general correlation between NOyand CO may be due to instrumental limitations and to variable sinks for NOy. The average enrichment of ΔNOy/ΔCO was quite high, consistent with the efficient production of ozone observed in the plumes. The chemical characteristics of the haze layers, together with remote sensing information and trajectory calculations, suggest that fire emissions (in Africa and/or South America) are the primary source of

ISSN:0148-0227    

DOI:10.1029/94JD00263

年代:1994

数据来源: WILEY

摘要:

Since 1987, over 220 measurements of the SO2flux at Mount Etna have been carried out using a correlation spectrometer (COSPEC) with different measuring techniques (mainly with COSPEC mounted on a ground‐based vehicle). This paper reports and analyzes the data obtained between October 1987 and December 1991. During this period, three distinct time intervals characterized by particular SO2emission patterns were identified. The first interval (A) showed a mean SO2flux of 5500 t/d associated with relatively quiet summit crater eruptive activity. The second interval (B) included two eruptive periods, September–October 1989 and January–February 1990, associated with high fluxes reaching 10,000–25,000 t/d. The third interval (C) started in concert with a regional earthquake (December 13, 1990) and showed first a decrease and then an increase of SO2emissions before the onset of the major 1991–1993 flank eruption. Analysis of the data reveals a cyclic pattern to the SO2emissions over prolonged periods; a nearly constant supply of SO2from the volcano's main feeder system, especially evident in the long term; a two‐ to fivefold increase above mean flux values (from 10,000 to 25,000 t/d) when occurring with paroxysmal eruptive activity; and minimal flux values (∼1000 t/d) about 1 month prior to important er

ISSN:0148-0227    

DOI:10.1029/94JD00224

年代:1994

数据来源: WILEY

摘要:

We measured total nitrate (TN) concentrations (defined as nitric acid vapor plus nitrate aerosol) nightly at the Mauna Loa Observatory (MLO) from September 1988 to September 1991. Using three meteorological criteria, (condensation nuclei, wind direction, and dew point) we selected samples that represented the free troposphere. The 3‐year mean and median of TN mixing ratios were 113 parts per trillion by volume (pptv) and 93 pptv, respectively. Each year the TN concentrations at MLO during the spring and summer were larger by more than a factor of 2 than those during the fall and winter. The springtime peak TN corresponded to incidents of increased Asian dust over the northern Pacific Ocean. Isentropic back trajectories confirmed that spring air masses with high TN originated over the Asian continent. Back trajectories also indicated that the North American continent was often the source of high TN during the summer. Air mass source regions and flow patterns to MLO were classified into five distinct groups of trajectories by cluster analysis.Despite the different source regions for each of the clusters the distributions of TN were very similar. This suggests that the source region may be less important for determining TN at MLO than such factors as the degree of vertical mixing over source regions, stratospheric injection, and wet removal rate

ISSN:0148-0227    

DOI:10.1029/94JD00146

年代:1994

数据来源: WILEY

摘要:

The carbon monoxide (CO) reference scale created by the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory (NOAA/CMDL) is used to quantify measurements of CO in the atmosphere, calibrate standards of other laboratories and to otherwise provide reference gases to the community measuring atmospheric CO. This reference scale was created based upon a set of primary standards prepared by gravimetric methods at CMDL and has been propagated to a set of working standards. In this paper we compare CO mixing ratios assigned to the working standards by three approaches: (1) calibration against the original gravimetric standards, (2) calibration using only working standards as the reference gas, and (3) calibration against three new gravimetric standards prepared at CMDL. The agreement between these values was typically better than 1%. The calibration histories of CMDL working standards are reviewed with respect to expected rates of CO change in the atmosphere. Using a Monte Carlo approach to simulate the effect of drifting standards on calculated mixing ratios, we conclude that the error solely associated with the maintenance of standards will limit the ability to detect small CO changes in the atmosphere. We also report results of intercalibration experiments conducted between CMDL and the Diode Laser Sensor Group (DACOM) at the NASA Langley Research Center (Hampton, Virginia), and CMDL and the Fraunhofer‐Institut (Garmisch‐Partenkirchen, Germany). Each laboratory calibrated several working standards for CO using their reference gases, and these results were compared to calibrations conducted by CMDL. The intercomparison of eight standards (CO concentrations between ∼100 and ∼165 ppb) by CMDL and NASA agreed to better than ±2%. The calibration of six standards (CO concentrations between ∼50 and ∼210 ppb) by CMDL and the Fraunhofer‐Institut agreed to within ±2% for four standards, and to within ±5% for a

ISSN:0148-0227    

DOI:10.1029/94JD00314

年代:1994

数据来源: WILEY

摘要:

A climatology of the vertical ozone distribution in the troposphere is obtained by balloon‐borne Brewer‐Mast sondes at the Observatoire de Haute Provence (OHP), southern France (44°N, 6°E, 700 m above sea level), during the period 1984 to 1990. The tropospheric ozone seasonal variation is characterized by a large maximum in spring and summer. A comparison to other ozone sounding stations gives evidence for a meridional ozone gradient in the middle and upper troposphere in Western Europe, with larger ozone values at Uccle (51°N, 4°E) and Jülich (50°N, 6°E) than at the OHP (44°N, 6°E.). A statistical analysis of ozone concentrations together with potential vorticity, a tracer of stratospheric air masses, shows a partial but significant correlation between both variables (r= 0.40, significance>99.9%), implying a noticeable impact of stratosphere‐troposphere exchange on the ozone variability. Concerning the spring/summer maximum of tropospheric ozone, it is shown to be caused both by ozone transfer from the stratosphere and by in situ photochemical ozone production. A climatology of the ozone/potential vorticity ratio is established for the OHP and its altitude and seasonal dependence is given. Finally, it is shown that the interannual variability of potential vorticity can cause dynamically induced trends of the ozone concentrations, which have to be taken into account to determine accurately the relative part due to

ISSN:0148-0227    

DOI:10.1029/94JD00228

年代:1994

数据来源: WILEY

摘要:

Concentrations of7Be and210Pb in 2 years of weekly high‐volume aerosol samples collected at Alert, Northwest Territories, Canada, showed pronounced seasonal variations. We observed a broad winter peak in210Pb concentration and a spring peak in7Be. These peaks were similar in magnitude and duration to previously reported results for a number of stations in the Arctic Basin. Beryllium 10 concentrations (determined only during the first year of this study) were well correlated with those of7Be; the atom ratio10Be/7Be was nearly constant at 2.2 throughout the year. This relatively high value of10Be/7Be indicates that the stratosphere must constitute an important source of both Be isotopes in the Arctic troposphere throughout the year. A simple mixing model based on the small seasonal variations of10Be/7Be indicates an approximately twofold increase of stratospheric influence in the free troposphere in late summer. The spring maxima in concentrations of both Be isotopes at the surface apparently reflect vertical mixing in rather than stratospheric injections into the troposphere. We have merged the results of the Be‐based mixing model with weekly O3soundings to assess Arctic stratospheric impact on the surface O3budget at Alert. The resulting estimates indicate that stratospheric inputs can account for a maximum of 10–15% of the O3at the surface in spring and for less during the rest of the year. These estimates are most uncertain during the winter. The combination of Be isotopic measurements and O3vertical profiles could allow quantification of the contributions of O3from the Arctic stratosphere and lower latitude regions to the O3budget in the Arctic troposphere. Although at present the lack of a quantitative understanding of the temporal variation of O3lifetime in the Arctic troposphere precludes making definitive calculations, qualitative examples of the power of this approach are

ISSN:0148-0227    

DOI:10.1029/94JD00742

年代:1994

数据来源: WILEY

摘要:

We have studied the possibility of using the nonequilibrium of radon daughters as an atmospheric tracer. Over a 7‐month period, two daily measurements were taken, one in the early morning and another in the early afternoon at a sampling point with a continental climate. The Rn in the atmospheric air is determined by electroprecipitation of Ra A (218Po) ions, and the Ra B (214Pb) and Ra C (214Bi) daughter concentrations are evaluated by gamma spectrometry. The results show a great variation of the activity ratios Ra B/Rn and Ra C/Rn during the sampling period, depending on the time of measurements and weather conditions. The relations between the activity ratios Ra B/Rn and Ra B/Rn with the stability of the atmosphere has been studied. The stability of the atmosphere was established by two methods: Pasquill's and Turner's stability categories. In the second case, the relationship between the activity ratios Ra B/Rn and Ra C/Rn with stability was highe

ISSN:0148-0227    

DOI:10.1029/94JD00405

年代:1994

数据来源: WILEY

摘要:

The vertical transport by clouds of an inert tracer and its redistribution by complex West African circulations are examined using a two‐dimensional mesoscale meteorological model with explicit microphysics. The model reproduces the tropical distribution of clouds and precipitation along a meridional cross section over West Africa, corresponding to the position of the Intertropical Convergence Zone (ITCZ) during the dry and rainy seasons. The resulting redistribution of the inert tracer is therefore closely related to the northward migration of the ITCZ between January and July. The occurrence of biomass burning during the dry season is shown to be an important source of tracer enrichment at upper levels in the atmospher

ISSN:0148-0227    

DOI:10.1029/94JD00408

年代:1994

数据来源: WILEY

摘要:

The latest version of the National Center for Atmospheric Research community climate model (CCM2) contains a semi‐Lagrangian tracer transport scheme for the purpose of advecting water vapor and for including chemistry in the climate model. One way to diagnose the CCM2 transport is to simulate CFCl3in the CCM2 since it has a well‐known industry‐based source distribution and a photochemical sink and to compare the model results to Atmospheric Lifetime Experiment/Global Atmospheric Gases Experiment observations around the globe. In this paper we focus on this comparison and discuss the synoptic scale issues of tracer transport where appropriate. We compare the model and observations on both 12‐hour and monthly timescales. The higher‐frequency events allow us to diagnose the synoptic scale transport in the CCM2 associated with the observational sites and to determine uncertainties in our high‐resolution source distribution. We find that the CCM2 does simulate many of the key features such as pollution events and some seasonal transports, but there are still some dynamical features of tracer transport such as the storm track dynamics and cross‐equatorial flow that merit further study in both the model and the re

ISSN:0148-0227    

DOI:10.1029/94JD00271

年代:1994

数据来源: WILEY