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1.
Snow chamber and snow-pile experiments performed during the ‘Alert 2000’ campaign show significant release of NO, NO2, and HONO in steady ratios under the influence of irradiation. Both light and a minimal degree of heating are required to produce this effect. We suggest diffusion and re-distribution of NO3 in the form of HNO3 as an important step in the mechanism of active nitrogen release from the snowpack.  相似文献   

2.
Recent research has demonstrated that nitrogen oxides are transformed to nitrogen acids in indoor environments, and that significant concentrations of nitrous acid are present in indoor air. The purpose of the study reported in this paper has been to investigate the sources, chemical transformations and lifetimes of nitrogen oxides and nitrogen acids under the conditions existing in buildings. An unoccupied single family residence was instrumented for monitoring of NO, NO2, NOy, MONO, HNO3, CO, temperature, relative humidity, and air exchange rate. For some experiments, NO2 and HONO were injected into the house to determine their removal rates and lifetimes. Other experiments investigated the emissions and transformations of nitrogen species from unvented natural gas appliances. We determined that HONO is formed by both direct emissions from combustion processes and reaction of NO2 with surfaces present indoors. Equilibrium considerations influence the relative contributions of these two sources to the indoor burden of HONO. We determined that the lifetimes of trace nitrogen species varied in the order NO ~ HONO > NO2 >HNO3. The lifetimes with respect to reactive processes are on the order of hours for NO and HONO, about an hour for NO2, and 30 minutes or less for HNO3. The rapid removal of NO2 and long lifetime of HONO suggest that HONO may represent a significant fraction of the oxidized nitrogen burden in indoor air.  相似文献   

3.
Simultaneous measurements of nitrous acid (HONO) and nitrogen dioxide (NO2) using a differential optical absorption spectroscopy system, nitrogen oxide (NO) by an in situ chemiluminescence analyser and carbon dioxide (CO2) by a gas chromatographic technique were carried out in the Wuppertal Kiesbergtunnel. At high traffic density HONO concentrations of up to 45 ppbV were observed. However, at low traffic density unexpectedly high HONO concentrations of up to 10 ppbV were measured caused by heterogeneous HONO formation on the tunnel walls. In addition to the tunnel campaigns, emission measurements of HONO, NO2, NO and CO2 from different single vehicles (a truck, a diesel and a gasoline passenger car) were also performed. For the correction of the HONO emission data, the heterogeneous HONO formation on the tunnel walls was quantified by two different approaches (a) in different NO2 emission experiments in the tunnel without traffic and (b) on tunnel wall residue in the laboratory. The HONO concentration corrected for heterogeneous formation on the tunnel walls, in relation to the CO2 concentration can be used to estimate the amount of HONO, which is directly emitted from the vehicle fleet. From the measured data, emission ratios (e.g. HONO/NOx) and emission indices (e.g. mg HONO kg−1 fuel) were calculated. The calculated emission index of 88±18 mg HONO kg−1 fuel allows an estimation of the HONO emission rates from traffic into the atmosphere. Furthermore, the heterogeneous formation of HONO from NO2 on freshly emitted exhaust particles is discussed.  相似文献   

4.
Chemical actinometry was used to measure nitrate photolysis rate coefficients, JNO3, on and in snowpack at Summit, Greenland. Sealed glass tubes containing nitrate and a hydroxyl radical trapping system were buried in snow and exposed for between 2 and 24 h. Average JNO3 values for 2-h midday exposures in early June on surface snow were 10–14×10−7 s−1. Averages over 24 h were 3.5–4.5×10−7 s−1. These values reflect the integrated photon flux and also any variation of the nitrate photolysis rate with temperature. Attenuation of JNO3 within the firn was 0.03–0.04 cm−1 for 24-h exposures and 0.08 cm−1 for a 2-h exposure. Different attenuation coefficients may relate to differential light penetration due to changes in sun angle over the course of 24 h.  相似文献   

5.
The delta-Eddington radiation transfer model is used to calculate actinic fluxes and photolysis rates within the snow pack during the ALERT 2000 field campaign. Actinic fluxes are enhanced within the snow pack due to the high albedo of snow and conversion of direct light to diffuse light. The conversion of direct to diffuse light is highly dependent on the solar zenith angle, as demonstrated by model calculations. The optical properties of Alert snow are modeled as 100 μm radius ice spheres with impurity added to increase the absorption coefficient over that of pure water ice. Using these optical properties, the model achieves good agreement with observations of irradiance within the snow pack. The model is used to calculate the total actinic flux as a function of solar zenith angle and depth for either clear sky or cloudy conditions. The actinic flux is then used to calculate photochemical production of nitrogen oxides from nitrate photolysis assuming that nitrate in snow has the same absorption cross section and quantum yield in snow as in aqueous solution. Assuming all photo-produced nitrogen oxides are released to the gas phase, we derive a maximal flux of nitrogen oxides (NOx+HONO and possibly other products) from the snow pack. The value of this maximal flux depends critically on the assumed quantum yield for production of NO2, which is unknown in ice. Depending on the assumed quantum yield, the calculated maximal flux varies between values four times smaller than the observed NOx+HONO flux to five times larger than the NOx+HONO flux. Therefore, it appears that the calculated flux is in approximate agreement with the observations with a great need for improved understanding of nitrogen photochemistry in snow.  相似文献   

6.
Gas and aerosol measurements were made during the Polar Sunrise Experiment 2000 at Alert, Nunavut (Canada), using two independent denuder/filter systems for sampling and subsequent analysis by ion chromatography. Twelve to forty-eight hour samples were taken during a winter (9–21 February 2000) and a spring (17 April–5 May 2000) campaign. During the spring campaign, samples were taken at two different heights above the snow surface to investigate concentration differences. Total particulate NO3 is the most abundant inorganic nitrogen compound during Arctic springtime (mean 137.4 ng m−3). The NO3 fluxes were calculated above the snow surface to help identify processes that control snow–atmosphere exchange of reactive nitrogen compounds. We suggest that the observed fluxes of coarse particle NO3 via snow deposition may contribute to the nitrogen inventory in the snow surface. Measurements of surface snow provide experimental data that constrain the contribution of dry deposition of coarse particle NO3 to <7%. Wet deposition in falling snow appears to be the major contributor to the nitrate input to the snow.  相似文献   

7.
Wet and dry deposition were monitored at the University of Michigan Biological Station in rural northern Michigan for three winters. Dry deposition was measured by both the conventional bucket method and by measuring increases in concentration in exposed, elevated snow samples. Average results of the two methods were in reasonable agreement. The cumulative wet and dry deposition quantities are in good agreement with snowpack accumulations until the first thaw period. Dry deposition to snow accounts for less than 15% of the total H+, SO2−4, NO3 and NH+4 and approximately 25% of the Ca 2+, Mg 2+, Na+, K+ and Cl during an average precipitation year. Snowpack measurements were also made under deciduous and red pine canopies. Decreases in H+ and NO3 were observed under the red pine canopy.  相似文献   

8.
We report here direct observation by differential optical absorption spectroscopy (DOAS) of the formation of ppb levels of gaseous nitrous acid (MONO) from the reaction of ppm levels of nitrogen dioxide (NO2) with water vapor, in an indoor environment. The rate of formation of HONO displayed first order kinetics with respect to NO2 with a rate of (0.25 ±0.04) ppb min−1 per ppm of NO2 present. Assuming a lifetime of l h with respect to both physical and chemical removal processes for HONO, this leads to an estimated steady state concentration of ~ 15 ppb of HONO per ppm of NO2 present. This relatively high level of HONO associated with NO2-air mixtures raises new questions concerning the health implications of elevated NO2 concentrations in indoor environments e.g. HONO is a respirable nitrite known to convert secondary amines in vitro to carcinogenic nitrosamines.  相似文献   

9.
A chamber placed in a constant temperature freezing room was used to study the surface resistance during deposition of HNO3 to a snow surface. The resistance decreased with increasing temperature from larger than 5 s mm−1 at − 18°C to about l s mm−1 at −3°C. Measurements of gaseous and particulate nitrate concentrations during winter at a rural site in south central Sweden gave concentrations in the range of 0.4–5 μg HNO3 m−1 and 0.3–3 μg NO3 m−3 with a mean value of 1.3 μg HNO3 m−3 and 0.7 μg NO3 m−3, respectively. The results indicate that for periods with temperatures below − 2°C estimated dry deposition of HNO3 to snow is at most 4 % of measured wet deposition of nitrate in the area.  相似文献   

10.
Two new long pathlength spectrometers, utilizing 25-m basepath multiple reflection optical systems, were employed for the first time during an intercomparison of measurement methods for atmospheric nitrogenous species held at Claremont, CA, 11–19 September 1985. Measurement of nitrogenous species using these closed optical path systems, as opposed to single pass systems extending several kilometers, permit the resulting in situ absolute spectroscopic data to serve as benchmark values for point monitors employing denuders or filter packs. The FT-IR spectrometer was operated at a total pathlength of 1150 m and spectral resolution of 0.125 cm−1, with corresponding detection sensitivities of 160 nmolem−3 for HNO3 and 60 nmole m−3 for NH3 (4 and 1.5 ppb, respectively). Concurrent measurements of HONO, NO2 and NO3 radicals were conducted with the differential optical absorption spectrometer operated at 800 m total pathlength with detection limits of 24, 160 and 0.8 nmole m−3 (0.6, 4 and 0.02 ppb) for HONO, NO2, and NO3 radicals, respectively.  相似文献   

11.
Gaseous nitrogen dioxide (NO2) represents an oxidant that is present in relatively high concentrations in various indoor settings. Remarkably increased NO2 levels up to 1.5 ppm are associated with homes using gas stoves. The heterogeneous reactions of NO2 with adsorbed water on surfaces lead to the generation of nitrous acid (HONO). Here, we present a HONO source induced by heterogeneous reactions of NO2 with selected indoor paint surfaces in the presence of light (300 nm?<?λ?<?400 nm). We demonstrate that the formation of HONO is much more pronounced at elevated relative humidity. In the presence of light (5.5 W m?2), an increase of HONO production rate of up to 8.6?·?109 molecules cm?2 s?1 was observed at [NO2]?=?60 ppb and 50 % relative humidity (RH). At higher light intensity of 10.6 (W m?2), the HONO production rate increased to 2.1?·?1010 molecules cm?2 s?1. A high NO2 to HONO conversion yield of up to 84 % was observed. This result strongly suggests that a light-driven process of indoor HONO production is operational. This work highlights the potential of paint surfaces to generate HONO within indoor environments by light-induced NO2 heterogeneous reactions.  相似文献   

12.
In the present study, photocatalytic reactions of nitrogen oxides (NOx = NO + NO2) were studied on commercial TiO2 doped facade paints in a flow tube photoreactor under simulated atmospheric conditions. Fast photocatalytic conversion of NO and NO2 was observed only for the photocatalytic paints and not for non-catalytic reference paints. Nitrous acid (HONO) was formed in the dark on all paints studied, however, it efficiently decomposes under irradiation only on the photocatalytic samples. Thus, it is concluded that photocatalytic paint surfaces do not represent a daytime source of HONO, in contrast to other recent studies on pure TiO2 surfaces. As main final product, the formation of adsorbed nitric acid/nitrate anion (HNO3/NO3?) was observed with near to unity yield. In addition, traces of H2O2 were observed in the gas phase only in the presence of O2. Formation of the greenhouse gas nitrous oxide (N2O) could be excluded. The uptake kinetics of NO, NO2 and HONO was very fast under atmospheric conditions (e.g. γ(NO + TiO2) > 10?5). Thus, the uptake on urban surfaces (painted houses, etc.) will be limited by transport. For a hypothetically painted street canyon, an average reduction of nitrogen oxide levels of ca. 5% is estimated. Since the harmful HNO3/NO3? is formed on the surface of the photoactive paints, whereas it is formed in the gas phase in the atmosphere, the use of photocatalytic paints may also help to reduce acid deposition, e.g. on plants, or nitric acid related health issues.  相似文献   

13.
Atmospheric chemistry directly above snowpacks is strongly influenced by ultraviolet (UV) radiation initiated emissions of chemicals from the snowpack. The emission of gases from the snowpack to the atmosphere is in part due to chemical reactions between hydroxyl radical, OH (produced from photolysis of hydrogen peroxide (H2O2) or nitrate (NO3)) and impurities in the snowpack. The work presented here is a radiative-transfer modelling study to calculate the depth-integrated production rates of hydroxyl radical from the photolysis of hydrogen peroxide and nitrate anion in snow for four different snowpacks and for solar zenith angles 30°–90°. This work also demonstrates the importance of hydrogen peroxide photolysis to produce hydroxyl radical relative to nitrate photolysis with (a) different snowpacks, (b) different ozone column depths, and (c) snowpack depths. The importance of hydrogen peroxide photolysis over nitrate photolysis for hydroxyl radical production increases with increasing depth in snowpack, column ozone depth, and solar zenith angle. With a solar zenith angle of 60° the production of hydroxyl radical from hydrogen peroxide photolysis accounts for 91–99% of all hydroxyl radical production from hydrogen peroxide and nitrate photolysis.  相似文献   

14.
A new convenient measurement method of nitrogen oxides (NOx) in the ambient air was developed. The collection of NOx is performed by an annular diffusion scrubber coated with a mixture of titanium dioxide (TiO2) and hydroxyapatite (Ca10(PO4)6(OH)2) and the analysis is carried out by ion chromatography with conductivity detection. Under ultraviolet light (UV) illumination, TiO2 produces reactive oxygen species such as super oxide (O2), hydroxyl radical (OH·) and peroxyhydroxyl radical (HO2·), by which nitric oxide (NO) is oxidized to nitrogen dioxide (NO2), and is further oxidized to nitric acid (HNO3). The yielded HNO3 and NO2 are effectively adsorbed on the surface of TiO2 and hydroxyapatite. The collection efficiencies of NO and NO2 by the annular diffusion scrubber coated with the catalysts under UV illumination are higher than 98%, respectively, at the air flow rate of 0.2–1.0 l min−1. After the collection of NOx, by feeding deionized water into the annular diffusion scrubber, HNO3 and NO2 which adsorbed on the catalysts are extracted as forms of nitrite ion (NO2) and nitrate ion (NO3). The extraction efficiencies of NO and NO2 are almost 100%. The activity of the washed catalysts can be completely recovered by drying with the purified air. Further, a simultaneous separated measurement of NO and NO2 can be performed by utilizing the UV illumination dependence. This method was applied to the measurement of NOx in the ambient air. The NOx concentration measured by this method was in good agreement with that obtained using the chemiluminescence NOx analyzer.  相似文献   

15.
We analyse the air quality data measured at a green area of Buenos Aires City (Argentina) during 38 days in winter. We study the relationships between ambient concentrations of nitric oxide (NO), nitrogen dioxide (NO2), ozone (O3) and nitrogen oxides (NOx=NO+NO2). The variation of the level of oxidant (OX=O3+NO2) with the NOx is obtained. It can be seen that the level of OX at a given location is made up of two contributions: one independent and another dependent on the NOx concentration. The first one can be considered as a regional contribution, equivalent to the background O3 concentration and the second one as a local contribution that depends on the level of primary pollution. Local oxidant sources may include direct NO2 emissions, the reaction of NO with O2 at high-NOx levels, and the emission of species that promote the conversion of NO to NO2. The final category of emissions may include the nitrous acid (HONO) that is emitted directly in vehicle exhaust. Finally, we present a diurnal variation of the local as well as regional contributions and the dependence of the last one on wind direction.  相似文献   

16.
Static chamber method was adopted to measure the surface exchanges of NO and NO2 between three kinds of agricultural lands and the atmosphere during spring–summer period in the Yangtze Delta, China. The average NO fluxes were 20.9, 27.4 and 21.4 ng N m−2 s−1, respectively, for cabbage (CA, cultivation of celery occurred along with cabbage), potato (PO) and soybean (SY) fields. The average NO2 fluxes were −1.12, 0.93 and −0.68 ng N m−2 s−1, respectively, for the cabbage, potato and soybean fields. Apparently, negative linear correlation was found between the NO2 fluxes from the CK plot (tilled conventionally but did not cultivate any seeds) and its ambient concentrations, and the compensation point was calculated to be 0.92 ppbv. The total NO emission from the vegetable lands and SY land in this region during spring–summer period was roughly estimated to be 15.9 Gg N, which accounted for about 11.2% of the estimated value of total NO emissions in the July of 1999 from Chinese agricultural fields.  相似文献   

17.
Laboratory studies on the heterogeneous conversion of nitrogen dioxide into nitrous acid on irradiated ice films containing humic acid are described. It was found that the presence of light in the visible range of the solar spectrum significantly enhances the rate of nitrous acid release from a humic acid doped ice film. This process might contribute to observed HONO production in snow, where the NO2 is thought to originate from nitrate photolysis. Analysis of the experimental data based on the Langmuir Hinshelwood model framework allowed quantification of the observed dependencies of the nitrous acid production rate on nitrogen dioxide concentration. The observed dependencies on the humic acid concentration as well as on the irradiation intensity were used to estimate light-driven HONO fluxes for environmental snow covers.  相似文献   

18.
Experiments were performed at Summit, Greenland (72°34′ N, 38°29′ W) to investigate hydroxyl mixing ratios in the sunlit surface snowpack (or firn). We added a carefully selected mixture of hydrocarbon gases (with a wide range of hydroxyl reactivities) to a UV and visible light transparent flow chamber containing undisturbed natural firn. The relative decrease in mixing ratios of these gases allowed estimation of the lower limit mixing ratio of hydroxyl radicals in the near-surface firn pore spaces. Hydroxyl mixing ratios in the firn air followed a diurnal cycle in summer 2003 (10–12 July), with peak values of more than 3.2×106 molecules cm−3 between 13:00 and 16:00 local time. The minimum value estimated was 1.1×106 molecules cm−3 at 20:00 local time. Results during spring of 2004 showed lower, but rapidly increasing, peak hydroxyl mixing ratios of 1.1×106 molecules cm−3 in the early afternoon on 15 April and 1.5×106 molecules cm−3 on 1 May. Our firn hydroxyl estimates were similar to directly measured above-snow ambient levels during the spring field season, but were only about 30% of ambient levels during summer.  相似文献   

19.
Measurements of NO and NO2 were made at a surface site (55.28 °N, 77.77 °W) near Kuujjuarapik, Canada during February and March 2008. NOx mixing ratios ranged from near zero to 350 pptv with emission from snow believed to be the dominant source. The amount of NOx was observed to be dependent on the terrain over which the airmass has passed before reaching the measurement site. The 24 h average NOx emission rates necessary to reproduce observations were calculated using a zero-dimensional box model giving rates ranging from 6.9 × 108 molecule cm?2 s?1 to 1.2 × 109 molecule cm?2 s?1 for trajectories over land and from 3.8 × 108 molecule cm?2 s?1 to 6.6 × 108 molecule cm?2 s?1 for trajectories over sea ice. These emissions are higher than those suggested by previous studies and indicate the importance of lower latitude snowpack emissions. The difference in emission rate for the two types of snow cover shows the importance of snow depth and underlying surface type for the emission potential of snow-covered areas.  相似文献   

20.
Results are presented of airborne measurements taken in oil sands extraction plant plumes in Fort McMurray, Alberta, Canada. Measurements with fast response monitors at a high sampling rate illustrate the narrow reaction zone in the plume caused by a turbulent diffusion reaction of NO to NO2 as suggested by theoretical and laboratory studies. The measured conversion rates of NO to NO2 varied considerably from day to day, from 0.2 to 21.4% min. Analysis of the oxidation rate of NO to NO2 and of the atmospheric turbulence parameter reveals that, over the distances and time scales within which the plumes are distinguishable from the background, the nitrogen oxides chemistry in the plumes is controlled by the rates at which the plumes mix with the ambient air (containing ozone), rather than by chemical kinetics.  相似文献   

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