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1.
Continuous in-situ measurements of surface ozone (O 3), carbon monoxide (CO) and oxides of nitrogen (NOx) were conducted at Udaipur city in India during April 2010 to March 2011. We have analyzed the data to investigate both diurnal and seasonal variations in the mixing ratios of trace gases. The diurnal distribution of O 3 showed highest values in the afternoon hours and lower values from evening till early morning. The mixing ratios of CO and NOx showed a sharp peak in the morning hours but lowest in the afternoon hours. The daily mean data of O 3, CO and NOx varied in the ranges of 5–51 ppbv, 145–795 ppbv and 3–25 ppbv, respectively. The mixing ratios of O 3 were highest of 28 ppbv and lowest 19 ppbv during the pre-monsoon and monsoon seasons, respectively. While the mixing ratios of both CO and NOx showed highest and lowest values during the winter and monsoon seasons, respectively. The diurnal pattern of O 3 is mainly controlled by the variations in photochemistry and planetary boundary layer (PBL) depth. On the other hand, the seasonality of O 3, CO and NOx were governed by the long-range transport associated mainly with the summer and winter monsoon circulations over the Indian subcontinent. The back trajectory data indicate that the seasonal variations in trace gases were caused mainly by the shift in long-range transport pattern. In monsoon season, flow of marine air and negligible presence of biomass burning in India resulted in lowest O 3, CO and NOx values. The mixing ratios of CO and NOx show tight correlations during winter and pre-monsoon seasons, while poor correlation in the monsoon season. The emission ratio of ?CO/?NOx showed large seasonal variability but values were lower than those measured over the Indo Gangetic Plains (IGP). The mixing ratios of CO and NOx decreased with the increase in wind speed, while O 3 tended to increase with the wind speed. Effects of other meteorological parameters in the distributions of trace gases were also noticed. 相似文献
2.
We have studied long-term changes in tropospheric NO 2 over South India using ground-based observations, and GOME and OMI satellite data. We have found that unlike urban regions, the region between Eastern and Western Ghat mountain ranges experiences statistically significant decreasing trend. There are few ground-based observatories to verify satellite based trends for rural regions. However, using a past study and recent measurements we show a statistically significant decrease in NO X and O 3 mixing ratio over a rural location (Gadanki; 13.48° N, 79.18° E) in South India. In the ground-based records of surface NO X, the concentration during 2010–11 is found to be lower by 0.9 ppbv which is nearly 60 % of the values observed during 1994–95. Small but statistically significant decrease in noon-time peak ozone concentration is also observed. Noon-time peak ozone concentration has decreased from 34?±?13 ppbv during 1993–96 to 30?±?15 ppbv during 2010–11. NO X mixing ratios are very low over Gadanki. In spite of low NO X values (0.5 to 2 ppbv during 2010–11), ozone mixing ratios are not significantly low compared to many cities with high NO X. The monthly mean ozone mixing ratio varies from 9 ppbv to 37 ppbv with high values during Spring and low values during late Summer. Using a box-model, we show that presence of VOCs is also very important in addition to NO X in determining ozone levels in rural environment and to explain its seasonal cycle. 相似文献
3.
The seasonal and diurnal variations of ozone mixing ratios have been observed at Niwot Ridge. Colorado. The ozone mixing ratios have been correlated with the NO
x
(NO+NO 2) mixing ratios measured concurrently at the site. The seasonal and diurnal variations in O 3 can be reasonably well understood by considering photochemistry and transport. In the winter there is no apparent systematic diurnal variation in the O 3 mixing ratio because there is little diurnal change of transport and a slow photochemistry. In the summer, the O 3 levels at the site are suppressed at night due to the presence of a nocturnal inversion layer that isolated ozone near the surface, where it is destroyed. Ozone is observed to increase in the summer during the day. The increases in ozone correlate with increasing NO
x
levels, as well as with the levels of other compounds of anthropogenic origin. We interpret this correlation as in-situ or in-transit photochemical production of ozone from these precursors that are transported to our site. The levels of ozone recorded approach 100 ppbv at NO
x
mixing ratios of approximately 3 ppbv. Calculations made using a simple clean tropospheric chemical model are consistent with the NO
x
-related trend observed for the daytime ozone mixing ratio. However, the chemistry, which does not include nonmethane hydrocarbon photochemistry, underestimates the observed O 3 production. 相似文献
4.
In the present study, an attempt has been made to examine the governing photochemical processes of surface ozone (O 3) formation in rural site. For this purpose, measurements of surface ozone and selected meteorological parameters have been
made at Anantapur (14.62°N, 77.65°E, 331 m asl), a semi-arid zone in India from January 2002 to December 2003. The annual
average diurnal variation of O 3 shows maximum concentration 46 ppbv at noon and minimum 25 ppbv in the morning with 1σ standard deviation. The average seasonal
variation of ozone mixing ratios are observed to be maximum (about 60 ppbv) during summer and minimum (about 22 ppbv) in the
monsoon period. The monthly daytime and nighttime average surface ozone concentration shows a maximum (55 ± 7 ppbv; 37 ± 7.3 ppbv)
in March and minimum (28 ± 3.4 ppbv; 22 ± 2.3 ppbv) in August during the study period. The monthly average high (low) O 3 48.9 ± 7.7 ppbv (26.2 ± 3.5 ppbv) observed at noon in March (August) is due to the possible increase in precursor gas concentration
by anthropogenic activity and the influence of meteorological parameters. The rate of increase of surface ozone is high (1.52 ppbv/h)
in March and lower (0.40 ppbv/h) in July. The average rate of increase of O 3 from midnight to midday is 1 ppbv/h. Surface temperature is highest (43–44°C) during March and April months leading to higher
photochemical production. On the other hand, relative humidity, which is higher during the rainy season, shows negative correlation
with temperature and ozone mixing ratio. It can be seen that among the two parameters are measured, correlation of surface
ozone with wind speed is better ( R
2=0.84) in compare with relative humidity ( R
2=0.66). 相似文献
5.
This study examines the processes controlling the diurnal variability of ozone (O 3) in the marine boundary layer of the Kwajalein Atoll, Republic of the Marshall Islands (latitude 8° 43′ N, longitude 167°
44′ E), during July to September 1999. At the study site, situated in the equatorial Pacific Ocean, O 3 mixing ratios remained low, with an overall average of 9–10 parts per billion on a volume basis (ppbv) and a standard deviation
of 2.5 ppbv. In the absence of convective storms, daily O 3 mixing ratios decreased after sunrise and reached minimum during the afternoon in response to photochemical reactions. The
peak-to-peak amplitude of O 3 diurnal variation was approximately 1–3 ppbv. During the daytime, O 3 photolysis, hydroperoxyl radicals, hydroxyl radicals, and bromine atoms contributed to the destruction of O 3, which explained the observed minimum O 3 levels observed in the afternoon. The entrainment of O 3-richer air from the free troposphere to the local marine boundary layer provided a recovery mechanism of surface O 3 mixing ratio with a transport rate of 0.04 to 0.2 ppbv per hour during nighttime. In the presence of convection, downward
transport of O 3-richer tropospheric air increased surface O 3 mixing ratios by 3–12 ppbv. The magnitude of O 3 increase due to moist convection was lower than that observed over the continent (as high as 20–30 ppbv). Differences were
ascribed to the higher O 3 levels in the continental troposphere and weaker convection over the ocean. Present results suggest that moist convection
plays a role in surface-level O 3 dynamics in the tropical marine boundary layer. 相似文献
6.
Measurements of surface O 3, CO, NO x and light NMHCs were made during December 2004 at Hissar, a semi-urban site in the state of Haryana in north-west region
of the Indo-Gangetic Plain (IGP). The night-time O 3 values were higher when levels of CO, NO and NO 2 were lower but almost zero values were observed during the episodes of elevated mixing ratios of CO (above 2000 ppbv) and
NO x (above 50 ppbv). Slopes derived from linear fits of O 3 versus CO and O 3 versus NO x scatter plots were also negative. However, elevated levels of O 3 were observed when CO and NO x were in the range of 200–300 ppbv and 20–30 ppbv, respectively. Slope of CO-NO x of about 33 ppbv/ppbv is much larger than that observed in the US and Europe indicating significant impact of incomplete
combustion processes emitting higher CO and lesser NO x. Correlations and ratios of these trace gases including NMHCs show dominance of recently emitted pollutants mostly from biomass
burning at this site. 相似文献
7.
Continuous measurements of SO 2, NO x and O 3 along with sampling based measurements of CO, CH 4, NMHCs and CO 2 were carried out during May, 2010 at Ahmedabad. The diurnal variations of SO 2 in ambient air exhibited elevated values during the night and lower levels during the sunlit hours. The mean concentration of SO 2 during the study period was 0.95 ± 0.88 ppbv. However, the ambient SO 2 exceeded 17 ppbv in the night of 20 May, 2010. On the same day, tropospheric columnar SO 2 from OMI showed almost 350% increase corroborating the surface observations over an extended height regime. This was also the highest columnar value of SO 2 during the summer of 2010. Columnar loadings were also found to be high for formaldehyde, precipitable water vapor and aerosol optical depth on 20 May. Elevated concentrations were also recorded for other trace gases like NO 2 and O 3. Analysis of related data of trace gases indicated characteristics of fresh emissions with dominant contributions from mobile sources during the study period. However, SO 2/NO 2 ratio of 0.36 during the event period on 20th May connotes non-local influences. Analyses of meteorological parameters suggest combined impacts of transport and inversion causing higher levels of SO 2 and other pollutants during 20?C21 May. Episodes of such enhancements may perturb chemical and radiative balance of the atmosphere. 相似文献
8.
The mixing ratios for ozone and NO x (NO+NO 2) have been measured at a rural site in the United States. From the seasonal and diurnal trends in the ozone mixing ratio over a wide range of NO x levels, we have drawn certain conclusions concerning the ozone level expected at this site in the absence of local photochemical production of ozone associated with NO x from anthropogenic sources. In the summer (June 1 to September 1), the daily photochemical production of ozone is found to increase in a linear fashion with increasing NO x mixing ratio. For NO x mixing ratios less than 1 part per billion by volume (ppbv), the daily increase is found to be (17±3) [NO x]. In contrast, the winter data (December 1 to March 1) indicate no significant increase in the afternoon ozone level, suggesting that the photochemical production of ozone during the day in winter approximately balances the chemical titration of ozone by NO and other pollutants in the air. The extrapolated intercept corresponding to [NO x]=0 taken from the summer afternoon data is 13% less than that observed from the summer morning data, suggesting a daytime removal mechanism for O 3 in summer that is attributed to the effects of both chemistry and surface deposition. No significant difference is observed in the intercepts inferred from the morning and afternoon data taken during the winter.The results contained herein are used to deduce the background ozone level at the measurement site as a function of season. This background is equated with the natural ozone background during winter. However, the summer data suggest that the background ozone level at our site is elevated relative to expected natural ozone levels during the summer even at low NO x levels. Finally, the monthly daytime ozone mixing ratios are reported for 0[NO x]0.2 ppbv, 0.3 ppbv[NO x]0.7 ppbv and 1 ppbv[NO x]. These monthly ozone averages reflect the seasonal ozone dependence on the NO x level. 相似文献
9.
Air samples were collected covering a full diurnal cycle during each month of the year 2002 at a mountaintop of Mt. Abu (24.6^∘ N, 72.7^∘ E, 1680 amsl). These samples were analyzed for C 2−C 4 NMHCs using a gas chromatograph (GC) equipped with flame ionization detector (FID). The seasonally averaged diurnal distributions of these NMHCs do not show significant variations in the summer season. While sharp peaks in the diurnal variation of some species during evening hours are additional features apart from higher levels in all NMHCs in the winter season. The seasonal variations in relatively long lived species (e.g. ethane, propane and acetylene) are observed to be more pronounced compared to those in reactive species (e.g. ethene, propene and butanes). The seasonal changes in transport patterns seem to be more dominant factor at this site for the observed variations in NMHCs than changes in OH radical concentration. The annual mean mixing ratios of ethane, ethene, propane, propene, i-butane, acetylene, and n-butane are 1.22 ± 0.58, 0.34 ± 0.24, 0.46
± 0.20, 0.17 ± 0.14, 0.21 ± 0.18, 0.41 ± 0.43, and 0.31 ± 0.35 ppbv, respectively. Only few pairs of NMHCs are observed to show good correlations, mainly due to transport of air masses with different degree of photochemical processing. A comparison of this measurement with data reported for other remote sites of the globe indicates lower levels of light NMHCs in the tropical sites. The annual mean mixing ratios of various C 2−C 4 NMHCs at Mt. Abu are lower by factors ranging between 3 to 9 compared to a nearest urban site of Ahmedabad. The annual mean propylene (propene) equivalent concentrations of about 1.12 and 8.62 ppbC were calculated for Mt. Abu and Ahmedabad, respectively. 相似文献
10.
Continuous measurements of ozone and its precursors including NO, NO 2, and CO at an urban site (32°03′N, 118°44′E) in Nanjing, China during the period from January 2000 to February 2003 are presented. The effects of local meteorological conditions and distant transports associated with seasonal changed Asian monsoons on the temporal variations of O 3 and its precursors are studied by statistical, backward trajectory, and episode analyses. The diurnal variation in O 3 shows high concentrations during daytime and low concentrations during late night and early morning, while the precursors show high concentrations during night and early morning and low concentrations during daytime. The diurnal variations in air pollutants are closely related to those in local meteorological conditions. Both temperature and wind speed have significant positive correlations with O 3 and significant negative correlations with the precursors. Relative humidity has a significant negative correlation with O 3 and significant positive correlations with the precursors. The seasonal variation in O 3 shows low concentrations in late autumn and winter and high concentrations in late spring and early summer, while the precursors show high concentrations in late autumn and winter and low concentrations in summer. Local mobile and stationary sources make a great contribution to the precursors, but distant transports also play a very important role in the seasonal variations of the air pollutants. The distant transport associated with the southeastern maritime monsoon contributes substantially to the O 3 because the originally clean maritime air mass is polluted when passing over the highly industrialized and urbanized areas in the Yangtze River Delta. The high frequency of this type of air mass in summer causes the fact that a common seasonal characteristic of surface O 3 in East Asia, summer minimum, is not observed at this site. The distant transports associated with the northern continental monsoons that dominate in autumn and winter are related to the high concentrations of the precursors in these two seasons. This study can contribute to a better understanding of the O 3 pollution in vast inland of China affected by meteorological conditions and the rapid urbanization and industrialization. 相似文献
11.
A coupled chemical/dynamical model (SOCOL-SOlar Climate Ozone Links) is
applied to study the impacts of future enhanced CO and NOx emissions
over eastern China on regional chemistry and climate. The result shows that
the increase of CO and NOx emissions has significant effects on
regional chemistry, including NOx, CO, O 3, and OH concentrations.
During winter, the CO concentration is uniformly increased in the northern
hemisphere by about 10 ppbv. During summer, the increase of CO has a
regional distribution. The change in O 3, concentrations near eastern
China has both strong seasonal and spatial variations. During winter, the
surface O 3, concentrations decrease by about 2 ppbv, while during summer
they increase by about 2 ppbv in eastern China. The changes of CO, NOx,
and O 3, induce important impacts on OH concentrations. The changes in
chemistry, especially O 3, induce important effects on regional climate.
The analysis suggests that during winter, the surface temperature decreases
and air pressure increases in central-eastern China. The changes of
temperature and pressure produce decreases in vertical velocity. We should
mention that the model resolution is coarse, and the calculated
concentrations are generally underestimated when they are compared to
measured results. However, because this model is a coupled
dynamical/chemical model, it can provide some useful insights regarding the
climate impacts due to changes in air pollutant emissions. 相似文献
12.
Measurements of surface ozone (O 3), nitric oxide (NO), nitrogen dioxide (NO 2), oxides of nitrogen (NO x=NO+NO 2) and meteorological parameters have been made at Agra (North Central India, 27°10??N, 78°05??E) in post monsoon and winter season. The diurnal variation in O 3 concentration shows daytime in situ photochemical production with diurnal maximum in noon hours ranging from 51 to 54 ppb in post monsoon and from 76 to 82 ppb in winter, while minimum (16?C24 ppb) during nighttime and early morning hours. Average 8-h O 3 concentration varied from 12.4 to 83.9 ppb. The relationship between meteorological parameters (solar radiation intensity, temperature, relative humidity, wind speed and wind direction) and surface O 3 variability was studied using principal component analysis (PCA), multiple linear regression (MLR) and correlation analysis (CA). PCA and MLR of daily mean O 3 concentrations on meteorological parameters explain up to 80 % of day to day ozone variability. Correlation with meteorology is strongly emphasized on days having strong solar radiation intensity and longer sunshine time. 相似文献
13.
Size-segregated aerosol particles were collected using a high volume MOUDI sampler at a coastal urban site in Xiamen Bay, China, from March 2018 to June 2020 to examine the seasonal characteristics of aerosol and water-soluble inorganic ions (WSIIs) and the dry deposition of nitrogen species. During the study period, the annual average concentrations of PM1, PM2.5, PM10, and TSP were 14.8?±?5.6, 21.1?±?9.0, 35.4?±?14.2 μg m?3, and 45.2?±?21.3 μg m?3, respectively. The seasonal variations of aerosol concentrations were impacted by the monsoon with the lowest value in summer and the higher values in other seasons. For WSIIs, the annual average concentrations were 6.3?±?3.3, 2.1?±?1.2, 3.3?±?1.5, and 1.6?±?0.8 μg m?3 in PM1, PM1-2.5, PM2.5–10, and PM>10, respectively. In addition, pronounced seasonal variations of WSIIs in PM1 and PM1-2.5 were observed, with the highest concentration in spring-winter and the lowest in summer. The size distribution showed that SO42?, NH4+ and K+ were consistently present in the submicron particles while Ca2+, Mg2+, Na+ and Cl? mainly accumulated in the size range of 2.5–10 μm, reflecting their different dominant sources. In spring, fall and winter, a bimodal distribution of NO3? was observed with one peak at 2.5–10 μm and another peak at 0.44–1 μm. In summer, however, the fine mode peak disappeared, likely due to the unfavorable conditions for the formation of NH4NO3. For NH4+ and SO42?, their dominant peak at 0.25–0.44 μm in summer and fall shifted to 0.44–1 μm in spring and winter. Although the concentration of NO3–N was lower than NH4–N, the dry deposition flux of NO3–N (35.77?±?24.49 μmol N m?2 d?1) was much higher than that of NH4–N (10.95?±?11.89 μmol N m?2 d?1), mainly due to the larger deposition velocities of NO3–N. The contribution of sea-salt particles to the total particulate inorganic N deposition was estimated to be 23.9—52.8%. Dry deposition of particulate inorganic N accounted for 0.95% of other terrestrial N influxes. The annual total N deposition can create a new productivity of 3.55 mgC m?2 d?1, accounting for 1.3–4.7% of the primary productivity in Xiamen Bay. In light of these results, atmospheric N deposition could have a significant influence on biogeochemistry cycle of nutrients with respect to projected increase of anthropogenic emissions from mobile sources in coastal region. 相似文献
14.
The applicability of the tungsten oxide denuder tube technique for the measurement of ammonia in the rural troposphere was investigated. The technique is based on selective chemisorption of NH 3 from a gas stream, thermal desorption, conversion to NO, and analysis by NO–O 3 chemiluminescence. Nitric acid, which is also collected and desorbed as NO, was distinguished from NH 3 by differences in desorption temperature. Substituted amines were also collected, but desorbed at a slightly lower temperature than NH 3 in dry air. At high relative humidities, alkylamines may be hydrolyzed to NH 3 on the denuder surface and hence detected as NH 3. Overheating of the denuder tube during the temperature-programmed desorption was found to cause significant irreversible degradation of system performance.The technique was used to measure NH 3 mixing ratios at two rural locations in the United States. At a mountain site in Colorado during the winter of 1984, the average NH 3 mixing ratio was 0.20 ppbv (=0.08 ppbv). At an isolated coastal site in northern California during the spring of 1985, the average NH 3 mixing ratio was 0.36 ppbv (=0.17 ppbv). Correlations of the latter measurements with wind direction and NO
x
level suggest that the NH 3 mixing ratio in Pacific marine air at 40°N is <-0.25 ppbv. 相似文献
15.
The North China Plain (NCP) has recently faced serious air quality problems as a result of enhanced gas pollutant emissions due to the process of urbanization and rapid economic growth. To explore regional air pollu- tion in the NCP, measurements of surface ozone (O3), nitrogen oxides (NOx), and sulfur dioxide (SO2) were car- ried out from May to November 2013 at a rural site (Xianghe) between the twin megacities of Beijing and Tianjin. The highest hourly ozone average was close to 240 ppbv in May, followed by around 160 ppbv in June and July. High ozone episodes were more notable than in 2005 and were mainly associated with air parcels from the city cluster in the hinterland of the polluted NCP to the southwest of the site. For NOx, an important ozone precur- sor, the concentrations ranged from several ppbv to nearly 180 ppbv in the summer and over 400 ppbv in the fall. The occurrence of high NOx concentrations under calm condi- tions indicated that local emissions were dominant in Xianghe. The double-peak diurnal pattern found in NOx concentrations and NO/NOx ratios was probably shaped by local emissions, photochemical removal, and dilution re- sulting from diurnal variations of surface wind speed and the boundary layer height. A pronounced SO2 daytime peak was noted and attributed to downward mixing from an SO2-rich layer above, while the SO2-polluted air mass transported from possible emission sources, which differed between the non-heating (September and October) and heating (November) periods, was thought to be responsible for night-time high concentrations. 相似文献
16.
Surface ozone (O 3) and fine particulate matter (PM 2.5) are dominant air pollutants in China. Concentrations of these pollutants can show significant differences between urban and nonurban areas. However, such contrast has never been explored on the country level. This study investigates the spatiotemporal characteristics of urban-to-suburban and urban-to-background difference for O 3 (Δ[O 3]) and PM 2.5 (Δ[PM 2.5]) concentrations in China using monitoring data from 1171 urban, 110 suburban, and 15 background sites built by the China National Environmental Monitoring Center (CNEMC). On the annual mean basis, the urban-to-suburban Δ[O 3] is ?3.7 ppbv in Beijing–Tianjin–Hebei, 1.0 ppbv in the Yangtze River Delta, ?3.5 ppbv in the Pearl River Delta, and ?3.8 ppbv in the Sichuan Basin. On the contrary, the urban-to-suburban Δ[PM 2.5] is 15.8, ?0.3, 3.5 and 2.4 μg m ?3 in those areas, respectively. The urban-to-suburban contrast is more significant in winter for both Δ[O 3] and Δ[PM 2.5]. In eastern China, urban-to-background differences are also moderate during summer, with ?5.1 to 6.8 ppbv for Δ[O 3] and ?0.1 to 22.5 μg m ?3 for Δ[PM 2.5]. However, such contrasts are much larger in winter, with ?22.2 to 5.5 ppbv for Δ[O 3] and 3.1 to 82.3 μg m ?3 for Δ[PM 2.5]. Since the urban region accounts for only 2% of the whole country’s area, the urban-dominant air quality data from the CNEMC network may overestimate winter [PM 2.5] but underestimate winter [O 3] over the vast domain of China. The study suggests that the CNEMC monitoring data should be used with caution for evaluating chemical models and assessing ecosystem health, which require more data outside urban areas. 相似文献
17.
Measurements of NO x,y were made at Alert, Nunavut, Canada (82.5° N, 62.3° W) during surface layer ozone depletion events. In spring 1998, depletion events were rare and occurred under variable actinic flux, ice fog, and snowfall conditions. NO y changed by less than 10% between normal, partially depleted, and nearly completely depleted ozone air masses. The observation of a diurnal variation in NO x under continuous sunlight supports a source from the snowpack but with rapid conversion to nitrogen reservoirs that are primarily deposited to the surface or airborne ice crystals. It was unclear whether NO x was reduced or enhanced in different stages of the ozone depletion chemistry because of variations in solar and ambient conditions. Because ozone was depleted from 15–20 ppbv to less than 1 ppbv in just over a day in one event it is apparent that the surface source of NO x did not grossly inhibit the removal of ozone. In another case ozone was shown to be destroyed to less than the 0.5 ppbv detection limit of the instrument. However, simple model calculations show that the rate of depletion of ozone and its final steady-state abundance depend sensitively on the strength of the surface source of NO x due to competition from ozone production involving NO x and peroxy radicals. The behavior of the NO/NO 2 ratio was qualitatively consistent with enhanced BrO during the period of active ozone destruction. The model is also used to emphasize that the diurnal partitioning of BrO x during ozone depletion events is sensitive to even sub ppbv variations in O 3. 相似文献
18.
The objectives of this study were to identify species and levels of volatile organic compounds (VOCs), and determine their
oxidation capacity in the rural atmosphere of western Senegal. A field study was conducted to obtain air samples during September
14 and September 15, 2006 for analyses of VOCs. Methanol, acetone, and acetaldehyde were the most abundant detected chemical
species and their maximum mixing ratios reached 6 parts per billion on a volume basis (ppbv). Local emission sources such
as firewood and charcoal burning strongly influenced VOC concentrations. The VOC concentrations exhibited little temporal
variations due to the low reactivity with hydroxyl radicals, with reactivity values ranging from 0.001 to 2.6 s −1. The conditions in this rural site were rather clean. Low ambient NO
x
levels limited ozone production. Nitrogen oxide (NO
x
) levels reached values less than 2 ppbv and maximum VOC/NO
x
ratios reached 60 ppbvC/ppbv, with an overall average of 2.4 ± 4.5 ppbvC/ppbv. This indicates that the rural western Senegal
region is NO
x
limited in terms of oxidant formation potential. Therefore, during the study period photochemical ozone production became
limited due to low ambient NO
x
levels. The estimated ozone formation reactivity for VOCs was low and ranged between −5.5 mol of ozone/mol of benzaldehyde
to 0.6 mol/mol of anthropogenic dienes. 相似文献
19.
Measurements of ground level ozone (O 3), nitrogen dioxide (NO 2) and meteorological parameters (air temperature, relative humidity and wind speed and direction) has been made for 3 years from March 2007 to February 2010 at Nagercoil (8.2°N, 77.5°E, 23 m above sea level), an equatorial rural coastal site of southern India. The monthly average of daytime maximum of O 3 concentrations ranged from 28 to 50 parts per billion (ppb) with an annual average of 19.8 ppb. Similarly, monthly average of NO 2 concentration ranged from 3.4 ppb to 7.7 ppb with an annual average of 5.3 ppb. The monthly variation of meteorological parameters shows the little changes being a coastal site. The estimated summer crops yield losses by 1.1–15.6 % from present O 3 concentration level associated with AOT40 index 3.1–5 ppm h. 相似文献
20.
In July 1974 an NO/O3 chemiluminescent instrument was used to obtain measurements of NO in the stratosphere during two balloon flights launched from Churchill (59°N, 95°W). On the first flight, an altitude profile was obtained in which the NO volume mixing ratio was observed to increase from 0.3 to 2.7 ppbv between 19 and 29.5 km. On the second flight, the mixing ratio was observed to increase from 0.25 to 2.7 ppbv between 19 and 29 km and to remain almost constant at about 2.7 ppbv from 29 to 34.5 km. On this flight, the sunset decay of NO was also obtained while the payload was at a constant float altitude of 34.5 km. These decay measurements are compared satisfactorily with the results obtained from a time dependent stratospheric model. 相似文献
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