摘要:

Concurrent measurements of selected odd nitrogen constituents, hydrocarbons, peroxides, organic acids, formaldehyde, and other species were made from May 1 to June 4, 1988, at the Mauna Loa Observatory. An introduction to the experiment and a description of some of its objectives are presented.

ISSN:0148-0227    

DOI:10.1029/91JD00945

年代:1992

数据来源: WILEY

摘要:

Meteorological data are presented and discussed for the period May 1 to June 4,1988, in support of the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). Isentropic trajectories were computed to determine air mass origins. Meteorological observations at the Mauna Loa Observatory and radiosonde observations from HiIo, Hawaii, are used to analyze local influences on air mass composition.

ISSN:0148-0227    

DOI:10.1029/91JD02299

年代:1992

数据来源: WILEY

摘要:

Measurements of the title species were made during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX) conducted between May 1 and June 4, 1988, at the Geophysical Monitoring for Climatic Change (GMCC) station at 3.4‐km elevation on the Island of Hawaii. Diurnal changes in the organic nitrates primarily resulted from the transition between downslope flow (usually free tropospheric air) and upslope flow (marine boundary layer or a mix of marine boundary layer and free tropospheric air, both influenced by island sources of precursors) characteristic of the site. Longer term trends in the mixing ratios reflected changes in air mass origins from mid‐latitudes to more tropical latitudes. The average mixing ratios in free tropospheric samples were peroxyacetyl nitrate (PAN, 17 pptv), peroxypropionyl nitrate (PPN, 0.3 pptv), methyl nitrate (MN, 4 pptv), and O3(43 ppbv). The organic nitrates (PAN, PPN, MN) represent minor components of the total odd nitrogen budget at the site. In free tropospheric samples, PAN, PPN, and MN constituted average percentages of 7%,<1%, and 2% of total odd nitrogen. In more tropical air masses, MN could constitute as much as 10% of total odd nitrogen. A photochemical model is used to investigate the sensitivity of free tropospheric PAN to local precursor concentrations. The observed mixing ratios of PAN are also contrasted with measurements made at continental surface sites and during aircraft progr

ISSN:0148-0227    

DOI:10.1029/91JD02288

年代:1992

数据来源: WILEY

摘要:

Measurements of ≥C3alkyl nitrates, perchlorethylene, and bromoform were made during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). The median mixing ratios of these compounds in free tropospheric air (3.4 km) were 2.3, 3.2, and .20 pptv, respectively. A diurnal variation in the concentration of these compound at Mauna Loa was driven by the local upslope/downslope circulation and by differences in the concentration of these species between the boundary layer and the free troposphere. Longer term variation was closely related to synoptic‐scale circulation of the North Pacific and to differences in the sources of air masses reaching Hawaii. Alkyl nitrates and their hydrocarbon precursors were present in nearly constant proportions during the experiment. This suggested the possibility that nitrate:hydrocarbon ratios may be determined near source regions and remain steady during long‐range transport. Reasonable correlation was observed also between alkyl nitrates and peroxyacetyl nitrate (PAN), but a more complex relationship was found between methyl and higher alkyl nitrates. In general, ≥C3alkyl nitrates were a significant component of the organic nitrate reservoir at Mauna Loa. However, ≥C3alkyl nitrates only accounted for<2% of total NOy. This evidence suggests that simple alkyl nitrates are not the source of “missing” odd nitrogen in the remo

ISSN:0148-0227    

DOI:10.1029/91JD01540

年代:1992

数据来源: WILEY

摘要:

Measurements of the apparent first‐order rate coefficient for NO2photodissociation (jNO2) were made using a chemical actinometer during the month of May 1988 at the Mauna Loa Observatory, Hawaii. Simultaneous measurements of the ultraviolet irradiance (E), obtained with an Eppley radiometer, allowed extensive testing of the semi‐empirical relationships betweenEandjNO2proposed by Madronich (1987a). More than 3700 simultaneous measurements ofjNO2andEwere obtained for solar zenith angles ranging from 4–90 degrees, and for different sky conditions (including clear skies, partial cloud cover, arid valley clouds below the horizon). For overhead clear skies, the NO2photodissociation rate coefficient derived from Eppley radiometer data, here denotedj′, was in good agreement with actinometric measurements,j′/jNO2=1.01±0.05(1σ). The actinometer‐radiometer relationship holds reasonably well even when low‐lying valley clouds are present. For the periods of overhead intermittent clouds, thej′values trackjNO2values well, but the observed ratio shows significantly more scatter and the average is somewhat less than unity: 0.93 ± 0.09 (1σ). Measurements taken with and without upward scattered and reflected radiation show that valley clouds can contribute to thejNO2values for the conditions encountered during the Mauna Loa Observatory Photoc

ISSN:0148-0227    

DOI:10.1029/91JD02289

年代:1992

数据来源: WILEY

摘要:

NO and NO2were simultaneously measured by photolytic conversion / chemiluminescence techniques during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). The field site, located at an elevation of 3.4 km on the north side of the Mauna Loa Volcano, was subject to two airflow regimes which typically corresponded to upslope (marine boundary layer plus island sources) conditions during the day and downslope (middle free tropospheric) conditions at night to mid‐morning. Median values of NOx(NOx= NO + NO2) were 37 and 31 pptv during upslope and downslope conditions, respectively, with the downslope measurements consistent with previous measurements made from aircraft in the middle free troposphere over the North Pacific. Although the difference in median NOxmixing ratios in the upslope and downslope regimes is small, the influence of island sources of NOxis apparent. Indeed, the median upslope values were approximately 2.5 times greater than measurements made previously in the remote marine boundary layer. The data have been examined according to downslope / free tropospheric and upslope air flow regimes for relationships between NOxand the various species that were measured simultaneously (e.g., peroxyacetyl nitrate (PAN), HNO3, NO3, NOy, O3, CO, and hydrocarbons). While positive correlations between NOxand O3and PAN were typically observed in free tropospheric air, these correlations were considerably weaker than those observed during previous campaigns. This is likely primarily due to the lower sampling altitude during the MLOPEX study. NOxand dew point temperature were weakly anticorrelated in free tropospheric air masses. Linear correlations between NOxand the peroxides, formaldehyde, alkyl nitrates, and hydrocarbons were also weak in the free tropospheric air masses at the MLO. NOx/NOywas typically on the order of 0.1–0.2 in free tropospheric flow. Considerably higher values of NOx/NOy, were occasionally observed under upslope conditions. The NOx/NOyand HNO3/NOxvalues obtained under downslope conditions were similar to those previously obtained during aircraft measurements in the middle free troposphere over the northeast Pacific. On the whole, the downslope air masses sampled appear to be characteristic of well‐aged, marine free tropospheric air, and this conclusion is supported by 10‐day trajectory a

ISSN:0148-0227    

DOI:10.1029/91JD02296

年代:1992

数据来源: WILEY

摘要:

Simultaneous measurements of [NO2], [NO], [O3], and the NO2photo‐dissociation rate coefficient,J2, were made during a one‐month field study in the spring of 1988 at Mauna Loa, Hawaii, and were used to evaluate the photostationary state ratio, ϕ =J2[NO2]/k1[NO][O3]. Over 5600 measurements were made for clear sky conditions, allowing a detailed comparison with photochemical theory. Values of ϕ determined from the observations were consistently higher than unity, approaching 2.0 for high sun, and indicated peroxy radical mixing ratios near 60 pptv. High sun values of ϕ were independent of NOx(NO + NO2), but correlated well with ozone and water vapor through the expression ϕ−1 = (0.11 ± 0.21) + (1.59 ± 0.64) × 10−3× ([H2O]/[O3])½. A photochemical box model is shown to give good agreement with the values of ϕ, the peroxy radical concentrations, and the correlations with physical and chemical environmental variables determined from the observations. The rate of photochemical production of ozone was estimated from measurements of ϕ, and the rate of photochemical ozone destruction was estimated from the box model. For free tropospheric air samples characteristic of altitudes near 3.4 km, the 24‐hour average net ozone production rate is shown to be −0.5 ppbv/d (net ozone destruction), and is determined primarily by

ISSN:0148-0227    

DOI:10.1029/91JD02287

年代:1992

数据来源: WILEY

摘要:

The concentrations of gas phase formic acid (HCOOH) and acetic acid (CH3COOH) were measured at the Mauna Loa, Observatory, Hawaii during the first three weeks (May 1–21, 1988) of the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). Daytime values were determined mostly during upslope conditions and represent marine boundary layer air modified by contact with the island of Hawaii. Mean values were 452 and 374 pptv for HCOOH and CH3COOH, respectively. Nighttime values were determined mostly during downslope conditions and represent air in the free troposphere near 3400 m above sea level. Mean values were 63 and 94 pptv for HCOOH and CH3COOH, respectively. Aerosol formate and acetate concentration were one to two orders of magnitude less than the gas phase concentration and ranged from less than a few pptv to nearly 50 ppt

ISSN:0148-0227    

DOI:10.1029/91JD02297

年代:1992

数据来源: WILEY

摘要:

Atmospheric methane, nonmethane hydrocarbons, and carbon monoxide were measured at the Mauna Loa Observatory on the island of Hawaii in May and June 1988. The daily island upslope/downslope circulation resulted in a variable mixture of boundary layer and free tropospheric air at the observatory. Mixing ratios of these gases were higher during upslope flow than during downslope flow. Mixing ratios characteristic of the free troposphere at this altitude were most often measured during nighttime, downslope flow. Local marine emissions of ethylene and propylene and emissions of isoprene from island vegetation were detected during upslope circulation, but ethylene and propylene were also often detected at night during downslope circulation, indicating that air sampled during nighttime downslope flow may have included some air recently transported from the marine boundary layer. Comparison of data for methane, carbon monoxide, ethane, and propane from in situ measurements with measurements made from canister samples collected during the experiment showed very good agreement. Fluxes of isoprene from selected dominant island flora were also measured.

ISSN:0148-0227    

DOI:10.1029/91JD02295

年代:1992

数据来源: WILEY

摘要:

Ambient air concentrations of nitric acid vapor and aerosol nitrate were measured above the remote North Pacific between May 1 and June 5, 1988, during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). Nighttime (free tropospheric) mean values were 30 pptv nitrate aerosol and 103 pptv nitric acid. Daytime values, representative of island‐modified marine boundary layer air, averaged 60 pptv aerosol and 130 pptv nitric acid. The measurements were generally consistent with previous measurements in the remote North Pacific including free tropospheric measurements of nitric acid during NASA's Global Tropospheric Experiment/Chemical Instrumentation Test and Evaluation (GTE/CITE 2). MLOPEX observations are smaller than model HNO3/NOxratios. However, the magnitude of this discrepancy is obscured by uncertainties, mainly in the model OH concentration and nitric acid photolysis rates. Nonetheless, large observed variations in the HNO3/NOxratio likely indicate significant loss of nitric acid, at least part of the time, by some process in addition to vapor phase photolysis and destruction by OH. Several processes are considered, but no firm conclusion is reache

ISSN:0148-0227    

DOI:10.1029/91JD02966

年代:1992

数据来源: WILEY