Surface ozone concentrations in Agra: links with the prevailing meteorological parameters

Measurements of surface ozone (O₃), nitric oxide (NO), nitrogen dioxide (NO₂), oxides of nitrogen (NO_x=NO+NO₂) 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 O₃ 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 O₃ 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 O₃ variability was studied using principal component analysis (PCA), multiple linear regression (MLR) and correlation analysis (CA). PCA and MLR of daily mean O₃ 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.     

Observation of hydrogen peroxide concentrations in a Japanese red pine forest

In order to study the concentrations of hydrogen peroxide (H₂O₂) and the factors controlling its concentrations, we monitored concentrations of H₂O₂ and other gases such as sulfur dioxide, ozone, and NO _x as well as meteorological factors such as air temperature, relative humidity, and wind direction/speed during eight measurement periods from 2000 to 2002 in a Japanese red pine forest in Japan. The H₂O₂ concentrations ranged from below 0.01 to 1.64 ppb, and analysis of the diurnal variation in H₂O₂ concentration showed high concentrations around noon, and low concentrations in the morning and late afternoon. The H₂O₂ concentrations were high in early summer, when O₃ concentration, temperature, and solar radiation were high, and were low in fall, when O₃ concentration, temperature, and solar radiation were low. We propose that O₃ concentration affects the production of H₂O₂ in the monitored region during the period under study, but that high H₂O₂ concentrations were sometimes caused by the transport of polluted air from urban regions. H₂O₂ concentrations decreased remarkably when SO₂ concentrations increased by transported volcanic emission on Miyake Island. In the absence of the effects of SO₂, H₂O₂ concentrations increased with increasing O₃ concentration and temperature.     

Measurements of ozone and its precursor nitrogen dioxide and crop yield losses due to cumulative ozone exposures over 40 ppb (AOT40) in rural coastal southern India

Measurements of ground level ozone (O₃), nitrogen dioxide (NO₂) 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 O₃ concentrations ranged from 28 to 50 parts per billion (ppb) with an annual average of 19.8 ppb. Similarly, monthly average of NO₂ 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 O₃ concentration level associated with AOT40 index 3.1–5 ppm h.     

Hydrogen peroxide measurements in the marine atmosphere

Hydrogen peroxide, one of the key compounds in multiphase atmospheric chemistry, was measured on an Atlantic cruise (ANT VII/1) of the German research vessel Polarstern from 15 September to 9 October 1988, in rain and ambient air by a chemiluminescence technique. For gas phase H₂O₂ cryogenic sampling was employed. The presented results show an increase of gas-phase mixing ratios of about 45 pptv per degree latitude between 50° N and 0°, and a maximum of 3.5 ppbv around the equator. Generally higher mixing ratios were observed in the Southern Hemisphere, with a clear diurnal variation. The H₂O₂ mixing ratio is correlated to the UV radiation intensity and to the temperature difference between air and ocean surface water.     

龙凤山大气近地层O3浓度变化及与其它因素的关系

研究首次在龙凤山区域大气本底站测得的地面Ｏ３浓度及其变化的资料表明,中国东北农村地面大气Ｏ３浓度总体水平不很高,但在少数特殊的天气条件下,时均浓度可超过国家二级标准。Ｏ３浓度存在明显的季节和日变化,其月平均浓度１９９５年１月最低（２７．５ｐｐｂ）,１９９４年１１月最高（４３．２ｐｐｂ）。Ｏ３日变化幅度夏季的晴天最大（２８ｐｐｂ）,冬季的阴天最小（８ｐｐｂ）。气象要素（尤其是风速、气温和相对湿度等）和ＮＯｘ与地面Ｏ３浓度有较密切的关系。用多变量分析法探讨了地面Ｏ３各指标随气象因子和ＮＯｘ共同变化的规律,并拟合了寒冷和温暖期里与地面Ｏ３日最高浓度、日最低浓度及日变化幅度有关的方程。     

Seasonality of tropospheric ozone and water vapor over Delhi,India: a study based on MOZAIC measurement data

Tropospheric distributions of ozone (O₃) and water vapor (H₂O) have been presented based on the Measurements of OZone and water vapor by Airbus In-Service AirCraft (MOZAIC) data over the metro and capital city of Delhi, India during 1996–2001. The vertical mixing ratios of both O₃ and H₂O show strong seasonal variations. The mixing ratios of O₃ were often below 40 ppbv near the surface and higher values were observed in the free troposphere during the seasons of winter and spring. In the free troposphere, the high mixing ratio of O₃ during the seasons of winter and spring are mainly due to the long-range transport of O₃ and its precursors associated with the westerly-northwesterly circulation. In the lower and middle troposphere, the low mixing ratios of ∼20–30 ppbv observed during the months of July–September are mainly due to prevailing summer monsoon circulation over Indian subcontinent. The summer monsoon circulation, southwest (SW) wind flow, transports the O₃-poor marine air from the Arabian Sea and Indian Ocean. The monthly averages of rainfall and mixing ratio of H₂O show opposite seasonal cycles to that of O₃ mixing ratio in the lower and middle troposphere. The change in the transport pattern also causes substantial seasonal variation in the mixing ratio of H₂O of 3–27 g/kg in the lower troposphere over Delhi. Except for some small-scale anomalies, the similar annual patterns in the mixing ratios of O₃ and H₂O are repeated during the different years of 1996–2001. The case studies based on the profiles of O₃, relative humidity (RH) and temperature show distinct features of vertical distribution over Delhi. The impacts of long range transport of air mass from Africa, the Middle East, Indian Ocean and intrusions of stratospheric O₃ have also been demonstrated using the back trajectory model and remote sensing data for biomass burning and forest fire activities.     

A 10-year study of background surface ozone concentrations on the island of Gozo in the Central Mediterranean

A 10-year study of surface ozone mixing ratios in the Central Mediterranean was conducted based on continuous ozone measurements from 1997 to 2006 by a background regional Global Atmospheric Watch (GAW) station on the island of Gozo. The mean annual maximum mixing ratio is of the order of 66 ppbv in April–May with a broad secondary maximum of 64 ppbv in July–September. No long-term increase or decrease in the background level of surface ozone could be observed over the last 10 years. This is contrary to observations made in the Eastern Mediterranean, where a slow decrease in the background ozone mixing ratio was observed over the past 7 years. Despite the very high average annual ozone mixing ratio exceeding 50 ppbv—in fact, the highest average background ozone mixing ratio ever measured in Europe—, the diurnal O _{3 max}/O _{3 min} index of <1.40 indicates that the island of Gozo is a good site for measuring background surface ozone. However, frequent photosmog events from June to September during the past 10 years with ozone mixing ratios exceeding 90 ppbv indicate that the Central Mediterranean is prone to long-range transport of air pollutants from Europe by northerly winds. This was particularly evident during the so-called “August heatwave” of the year 2003 when the overall ozone mixing ratio was 4.6 ppbv higher than the average of all other 9 months of August since 1997. Air mass back-trajectory analysis of the August 2003 photosmog episodes on Gozo confirmed that ozone pollution originated from the European continent. Regression analysis was used to analyse the 10-year data set in order to model the behaviour of the ozone mixing ratio in terms of the meteorological parameters of wind speed, relative humidity, global radiation, temperature, month of year, wind sector, atmospheric pressure, and time of day (predictors). Most of these predictors were found to significantly affect the ozone mixing ratios. From March to November, the monthly average of the AOT40 threshold value for the protection of crops and vegetation against ozone was constantly exceeded on Gozo during the past 10 years.     

On the Spatial Distribution and Seasonal Variation of Lower-Troposphere Ozone over Europe

Surface ozone data from 25 Europeanlow-altitude sites and mountain sites located between79°N and 28°N were studied. The analysiscovered the time period March 1989–February 1993.Average summer and winter O₃ concentrations inthe boundary layer over the continent gave rise togradients that were strongest in the north-west tosouth-east direction and west-east direction, respectively. WintertimeO₃ ranged from 19 to 27 ppbover the continent, compared to about 32 ppb at thewestern border, while for summer the continentalO₃ values ranged between 39 and 56 ppb and theoceanic mixing ratios were around 37 ppb. In the lowerfree troposphere average wintertime O₃ mixingratios were around 38 ppb, with only an 8 ppbdifference between 28°N and 79°N. For summerthe average O₃ levels decreased from about 55 ppbover Central Europe to 32 ppb at 79°N. Inaddition, O₃ and O_x(= O₃ + NO₂)in polluted and clean air were compared. Theamplitudes of the seasonal ozone variations increasedin the north-west to south-east direction, while thetime of the annual maximum was shifted from spring (atthe northerly sites) to late summer (at sites inAustria and Hungary), which reflected the contributionof photochemical ozone production in the lower partsof the troposphere.     

RESEARCH ON SURFACE O3 WITH METEOROLOGICAL CONDITIONS UNDER ATMOSPHERIC BACKGROUND CONDITIONS IN NORTHEAST CHINA*

Surface O₃ concentration and its precursors have been observed at Longfengshan station,Heilongjiang Province for a period of one year from August 13,1994 to July 30,1995. Relationship between surface O₃ and the meteorological conditions during this period is analyzed in this study.Observation results show that diurnal variation of surface O₃ follows a pattern of double-peaks with amplitude of 27-28 ppb under fine days in summer and autumn.Although the diurnal variation is small(14 ppb),it is still detectable when it is overcast.Diurnal variation of O₃ is irregular under rainy days.Surface O₃ concentration rises when wind speed starts to increase at 0800 BT(Beijing Time)from 0 to 6 m s^-1in autumn,winter and summer.Relative high surface O₃ concentration is noticed frequently when S,SSW,SW and WSW wind are encountered at the station during all seasons.At 0800 BT and 1400 BT the surface O₃ concentration increases with the increase of global radiation accordingly during fine days in winter,spring and autumn.During fine days average peak of O₃ concentration in summer is 20 ppb higher than that in winter while the average peak of global radiation in summer is almost twice as high as that in winter.The average surface O₃ concentration under fine days in autumn at Longfengshan station is 14 ppb lower in comparison to the observation results from Lin'an station where Lin'an is at about the same longitude and lower latitude,with same environment,which is mainly caused by the difference of global radiation due to different latitudes in these two areas(difference of average peak global radiation about 100 W m^-2).     

Chemistry of Halogen Oxides in the Troposphere: Comparison of Model Calculations with Recent Field Data

Reactive halogen species (RHS = X, XO, HOX, OXO; X = Cl, Br, I) are known to have an important influence on the chemistry in the polar boundary layer (BL), where they are responsible for ozone depletion events in spring. Recent field campaigns at Mace Head, Ireland, and the Dead Sea, Israel, identified for the first time iodine oxide (IO) at mixing ratios of up to 6.6 ppt and 90 ppt bromine oxide (BrO), respectively, by DOAS also at lower latitudes. These results intensified the discussion about the role of the RHS in the mid-latitude BL.Photochemical box model calculations show that the observed IO mixing ratios can destroy ~0.45 ppb ozone per hour. This is comparable to the rates of the known O₃-loss processes in the boundary layer. The model studies also reveal that IO, at these levels, has a strong influence on the BL photochemistry, increasing the OH/HO₂- and the NO₂/NO - ratios. In combination these changes lead to a reduction of the photochemical ozone formation, which - in addition - reduces ozone mixing ratios by up to 0.15 ppb/h.The studies for the Dead Sea case give no information on the heterogeneous process responsible for the bromine release, but they show that a total of 2 – 4 ppb of total bromine have to be released to explain the observed complete depletion of 60 ppb ozone in 2 – 3 hours.     

A study of ozone in the Colorado mountains

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+NO₂) mixing ratios measured concurrently at the site. The seasonal and diurnal variations in O₃ can be reasonably well understood by considering photochemistry and transport. In the winter there is no apparent systematic diurnal variation in the O₃ mixing ratio because there is little diurnal change of transport and a slow photochemistry. In the summer, the O₃ 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 O₃ production.     

Effects of high CO2 levels on surface temperature and atmospheric oxidation state of the early Earth

One-dimensional radiative-convective and photochemical models are used to examine the effects of enhanced CO₂ concentrations on the surface temperature of the early Earth and the composition of the prebiotic atmosphere. Carbon dioxide concentrations of the order of 100–1000 times the present level are required to compensate for an expected solar luminosity decrease of 25–30%, if CO₂ and H₂O were the only greenhouse gases present. The primitive stratosphere was cold and dry, with a maximum H₂O volume mixing ratio of 10^–6. The atmospheric oxidation state was controlled by the balance between volcanic emission of reduced gases, photo-stimulated oxidation of dissolved Fe⁺² in the oceans, escape of hydrogen to space, and rainout of H₂O₂ and H₂CO. At high CO₂ levels, production of hydrogen owing to rainout of H₂O₂ would have kept the H₂ mixing ratio above 2×10^–4 and the ground-level O₂ mixing ratio below 10^–11, even if no other sources of hydrogen were present. Increased solar UV fluxes could have led to small changes in the ground-level mixing ratios of both O₂ and H₂.     

A New Index Developed for Fast Diagnosis of Meteorological Roles in Ground-Level Ozone Variations

China experienced worsening ground-level ozone(O₂) pollution from 2013 to 2019. In this study, meteorological parameters, including surface temperature(T₂), solar radiation(SW), and wind speed(WS), were classified into two aspects,(1) Photochemical Reaction Condition(PRC = T₂× SW) and(2) Physical Dispersion Capacity(PDC = WS). In this way, a Meteorology Synthetic Index(MSI = PRC/PDC) was developed for the quantification of meteorology-induced ground-level O₂pollution. The positive linear relationship between the 90 th percentile of MDA8(maximum daily 8-h average) O₂concentration and MSI determined that the contribution of meteorological changes to ground-level O-3 varied on a latitudinal gradient, decreasing from ~40% in southern China to 10%–20% in northern China. Favorable photochemical reaction conditions were more important for ground-level O₂pollution. This study proposes a universally applicable index for fast diagnosis of meteorological roles in ground-level O₂variability, which enables the assessment of the observed effects of precursor emissions reductions that can be used for designing future control policies.     

Observation of Filterable Bromine Variabilities During Arctic Tropospheric Ozone Depletion Events in High (1hour) Time Resolution

The halogen ions Br^- and Cl^- together with NO₃ ^-, SO₄ ⁼, MSA^- (methane sulfonate), Na⁺ and NH₄ ⁺ were analysed by ion chromatography in extracts of more than 800 aerosol cellulose filter samples taken at Ny Ålesund, Svalbard (79°N, 12°E) in spring 1996 (March 27 - May 16) within the European Union project ARCTOC (Arctic Tropospheric Ozone Chemistry). Anticorrelated variations between f-Br (filterable bromine, i.e. water soluble bromine species that can be collected by aerosol filters) and ozone within the arctic troposphere were evaluated at a resolution of 1 or 2 hours for periods with depleted ozone and 4 hours at normal ozone. A mean f-Br concentration of 11 ng m^-3 (0.14 nmol m^-3) was observed for the whole campaign, while maximum concentrations of 80 ng m^-3 (1 nmol m^-3) were detected during two total O₃-depletion events (O₃ drop to mixing ratios below the detection limit of < 2 ppb). Anticorrelation between f-Br and O₃ was also seen during minor O₃-depletion episodes (sudden drop in O₃ by at least 10 ppb, but O₃ still exceeding the detection limit) and even for ozone variations near its background level (40-50 ppb). A time lag of about 10 hours between the change of ozone and of f-Br concentrations could only be found during a total ozone depletion event, when f-Br reached its maximum values several hours after ozone was totally destroyed. Bromine oxide (BrO) concentrations, measured by DOAS (Differential Optical Absorption Spectroscopy), and f-Br showed a coincident variability during almost the entire campaign (except in the case of total O₃-loss). Frequently enhanced anthropogenic nitrate and sulphate concentrations were observed during O₃-depletion periods. At O₃ concentrations < 10 ppb sulphate and nitrate exceed their typical mean level by 54% and 77%, respectively. This may indicate a possible connection between acidity and halogen release.     

Measurement of the NO + O3 Reaction Rate at Atmospheric Pressure Using Realistic Mixing Ratios

Accurate values for the rate and temperature dependence of the reaction NO + O₃ NO₂ + O₂ are important in the chemical modelling of photochemical processes in the atmosphere. Previous measurements have been made at low total pressures and/or with very large mixing ratios relative to those observed in the atmosphere. In this study the reaction rate has been measured using a novel approach under tropospheric conditions of temperature and pressure, and at tens of ppb (mixing ratios of 1 in 10⁸) between 263 and 328 K. The resultant Arrhenius expression (k=Ae^-Ea/RT) gives a larger activation energy (Ea/R=1670 ± 100) than the recommended literature value (Ea/R=1400 ± 200), and a larger pre-exponential factor (A=5.1 ± 1.6 × 10^-12 cf. recommended A=2.0 × 10^-12), but the second-order rate constant at 298 K (1.90 × 10^-14 molecules cm^-3 s^-1 ± 10%) is similar to the recommended value. The results confirm a lack of pressure dependence of the reaction, but were made over too small a range in temperature to address the issue of curvature of the simple Arrhenius expression.     

Ammonia measurements at Niwot Ridge,Colorado and point arena,California using the tungsten oxide denuder tube technique

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 NH₃ from a gas stream, thermal desorption, conversion to NO, and analysis by NO–O₃ chemiluminescence. Nitric acid, which is also collected and desorbed as NO, was distinguished from NH₃ by differences in desorption temperature. Substituted amines were also collected, but desorbed at a slightly lower temperature than NH₃ in dry air. At high relative humidities, alkylamines may be hydrolyzed to NH₃ on the denuder surface and hence detected as NH₃. 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 NH₃ mixing ratios at two rural locations in the United States. At a mountain site in Colorado during the winter of 1984, the average NH₃ mixing ratio was 0.20 ppbv (=0.08 ppbv). At an isolated coastal site in northern California during the spring of 1985, the average NH₃ mixing ratio was 0.36 ppbv (=0.17 ppbv). Correlations of the latter measurements with wind direction and NO _x level suggest that the NH₃ mixing ratio in Pacific marine air at 40°N is <-0.25 ppbv.     

Effects of tropospheric aerosols on the solar radiative heating in a clear atmosphere

Summary The broadband solar absorptivity concept is employed to parameterize the aerosol absorption effect. The solar radiation model developed by Liou and his associates was modified to incorporate the parameterization of solar radiative transfer in an aerosol layer. Comparison of the results from this method with other schemes exhibits close agreement. A Sahara dust storm case was also chosen to test the performance of the present model, and the computed heating rate profiles agree well with calculations based on optical properties derived from observations for both clear and dust cases. In general, enhanced heating due to aerosol absorption of solar flux occurs particularly in the lower troposphere (below 5 km). The heating rate is independent of the scattering partition factor (), but the planetary albedo increases with . Further study shows that the aerosol heating is sensitive to the surface albedo (r _s ) and to the cosine of the solar zenith angle (µ ₀). The decrease inr _s and/or increase inµ ₀ lower the solar heating rate, the planetary albedo and the atmospheric absorptivity, but raise the surface absorptivity due to reduced multiple reflection between the atmosphere and surface.With 9 Figures     

Low Ozone Episodes at Amphitrite Point Marine Boundary Layer Observatory,British Columbia,Canada

At Amphitrite Point, ozone (O₃) mixing ratios are observed to drop steadily to 5–15?ppb over a period of 12 hours or less with a frequency approaching one event per week (with highest frequencies occurring in summer and fall). Analysis of 47 such O₃ depletion events reveals that low O₃ episodes are a predominantly nocturnal phenomenon associated with anticyclonic conditions characterized by light onshore or alongshore winds and an absence of fog and mist. Back-trajectories show air carried to the Amphitrite Point Observatory (APO) during depletion events remains in the marine boundary layer and is not brought to the surface from aloft. There is no strong correlation with other “criteria” pollutants (CO, NO_x, SO₂, PM_2.5) that might be indicative of a mechanism for O₃ destruction linked to human, terrestrial, or marine pollutant sources. However, CO₂ mixing ratios are observed to increase, coincident with O₃ depletion. Together, these results point to a natural marine boundary layer phenomenon in which O₃ destruction dominates O₃ production and/or replenishment by vertical mixing. While there are several candidate mechanisms, the conditions for O₃ depletion (and CO₂ buildup) to occur are set by meteorology and, in particular, development of a stable marine boundary layer in which vertical mixing is suppressed. Support for this interpretation is provided by simultaneous increases in CO₂ in the stable marine boundary that are indicative of an important role played by marine biogenic processes (respiration). Future research should be directed at elucidating the chemical mechanisms responsible for O₃ destruction in the coastal zone, which means that there would be a need for a much broader range of measurements at APO (including halogenated species) as well as offshore measurements of both chemical and marine boundary layer meteorological variables.     

Solar eclipse-induced variations in solar flux, j(NO2) and surface ozone at Kannur, India

Surface ozone is mainly produced by the photodissociation of nitrogen dioxide (NO₂) by solar UV radiation. Subsequently, solar eclipses provide one of the unique occasions to explore the variations in the photolysis rate of NO₂ and their significant impact on the production of ozone at a location. This study aims to examine the diurnal variations in the photodissociation rate coefficient of NO₂, (j(NO₂*)), and mixing ratios of surface ozone and NO _X * (NO?+?NO₂*) during the solar eclipse that occurred on 15 January 2010 at Kannur (11.9°N, 75.4°E, 5?m amsl), a tropical coastal site on the Arabian Sea in South India. This investigation was carried out on the basis of the ground level observations of surface ozone and its prominent precursor NO₂*. The j(NO₂*) values were estimated from the observed solar UV-A flux data. A sharp decline in j(NO₂*) and surface ozone was observed during the eclipse phase because of the decreased efficiency of the ozone formation from NO₂. The NO₂* levels were found to increase during this episode, whereas the NO levels remained unchanged. The surface ozone concentration was reduced by 57.5%, whereas, on the other hand, that of NO _X * increased by 62.5% during the solar eclipse. Subsequently a reduction of *% in the magnitude of j(NO₂*) was found here during the maximum obscuration. Reductions in solar insolation, air temperature and wind speed were also observed during the solar eclipse event. The relative humidity showed a 6.4% decrease during the eclipse phase, which was a unique observation at this site.     

Measurements of surface ozone at semi-arid site Anantapur (14.62°N, 77.65°E, 331 m asl) in India

In the present study, an attempt has been made to examine the governing photochemical processes of surface ozone (O₃) 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 O₃ 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) O₃ 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 O₃ 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).