Seasonal Variation Of Ozone Research Articles

Reconstruction and searching ozone data periodicities in southern Brazil (29ºS, 53ºW)

Ozone plays a very important role in the nature due its characteristics as a natural filter of ultraviolet solar radiation. Thus, it is pertinent for the scientific community to understand all natural influence factors involving ozone along with a large time series. In this work, a reconstruction of ozone time series obtained by Brewer spectrophotometer from 1994 to 2008 at the Southern Space Observatory (SSO) - 29ºS, 53ºW - Southern Brazil is presented. TOMS-OMI data were used to follow the days without data, where a coefficient of correlation between TOMS-OMI and Brewer is acceptable around r = 0.89. Besides, wavelet analysis to determine the temporal evolution of the frequencies and the amplitudes was applied. Moreover, wavelet analysis aiming to determine the temporal evolution of the frequencies and the amplitudes was performed. The results pointed a period of 365 days (1 yr) for the seasonal variation of ozone, of 600 days attributed for a possible QBO influence and two periods of 2000 and other 4000 days regarding possibly to the second harmonic of the 11-year solar cycle.

Simulations over South Asia using the Weather Research and Forecasting model with Chemistry (WRF-Chem): chemistry evaluation and initial results

Abstract. This study presents annual simulations of tropospheric ozone and related species made for the first time using the WRF-Chem model over South Asia for the year 2008. The model-simulated ozone, CO, and NOx are evaluated against ground-based, balloon-borne and satellite-borne (TES, OMI and MOPITT) observations. The comparison of model results with surface ozone observations from seven sites and CO and NOx observations from three sites indicate the model's ability in reproducing seasonal variations of ozone and CO, but show some differences in NOx. The modeled vertical ozone distribution agrees well with the ozone soundings data from two Indian sites. The vertical distributions of TES ozone and MOPITT CO are generally well reproduced, but the model underestimates TES ozone, OMI tropospheric column NO2 and MOPITT total column CO retrievals during all the months, except MOPITT retrievals during August–January and OMI retrievals during winter. Largest differences between modeled and satellite-retrieved quantities are found during spring when intense biomass burning activity occurs in this region. The evaluation results indicate large uncertainties in anthropogenic and biomass burning emission estimates, especially for NOx. The model results indicate clear regional differences in the seasonality of surface ozone over South Asia, with estimated net ozone production during daytime (1130–1530 h) over inland regions of 0–5 ppbv h−1 during all seasons and of 0–2 ppbv h−1 over marine regions during outflow periods. The model results indicate that ozone production in this region is mostly NOx-limited. This study shows that WRF-Chem model captures many important features of the observations and gives confidence to using the model for understanding the spatio-temporal variability of ozone over South Asia. However, improvements of South Asian emission inventories and simulations at finer model resolution, especially over the complex Himalayan terrain in northern India, are also essential for accurately simulating ozone in this region.

Horizontal transport affecting trace gas seasonality in the Tropical Tropopause Layer (TTL)

We analyze horizontal transport from midlatitudes into the tropics (in‐mixing) and its impact on seasonal variations of ozone, carbon monoxide and water vapor in the Tropical Tropopause Layer (TTL). For this purpose, we use three‐dimensional backward trajectories, driven by ECMWF ERA‐Interim winds, and a conceptual one‐dimensional model of the chemical composition of the TTL. We find that the fraction of in‐mixed midlatitude air shows an annual cycle with maximum during NH summer, resulting from the superposition of two inversely phased annual cycles for in‐mixing from the NH and SH, respectively. In‐mixing is driven by the monsoonal upper‐level anticyclonic circulations. This circulation pattern is dominated by the Southeast Asian summer monsoon and, correspondingly, in‐mixing shows an annual cycle. The impact of in‐mixing on TTL mixing ratios depends on the in‐mixed fraction of midlatitude air and on the meridional gradient of the particular species. For CO the meridional gradient and consequently the effect of in‐mixing is weak. For water vapor, in‐mixing effects are negligible. For ozone, the meridional gradient is large and the contribution of in‐mixing to the ozone maximum during NH summer is about 50%. This in‐mixing contribution is not sensitive to the tropical ascent velocity, which is about 40% too fast in ERA‐Interim. As photochemically produced ozone in the TTL shows no distinct summer maximum, the ozone annual anomaly in the upper TTL turns out to be mainly forced by in‐mixing of ozone‐rich extratropical air during NH summer.

연안 대도시 해풍 풍하측 계곡지역의 지표오존 분포 특성: 계절변화와 바람과의 관계

The seasonal variations of ozone (O3) concentrations were investigated with regard to the relationship between O3 and wind distributions at two different sites (Jung Ang (JA): a semi-closed topography and Seo Chang (SC): a closed topography) within a valley city (Yangsan) and their comparison between these sites (JA and SC) and two non-valley sites (Dae Jeo (DJ) and Sang Nam (SN)) located downwind from coastal cities (Busan and Ulsan). This analysis was performed using the data sets of hourly O3 concentrations, meteorological factors (especially, wind speed and direction), and those on high O3 days exceeding the 8-h standard (60 ppb) during 2008-2009. In summer and fall (especially in June and October), the monthly mean values of the daily maximum O3 concentrations and the number of high O3 days at JA (and SC) were relatively higher than those at DJ (and SN). The increase in daytime O3 concentrations at JA in June was likely to be primarily impacted by the transport of O3 and its precursors from the coastal emission sources in Busan along the dominant southwesterly winds (about 5 m/s) under the penetration of sea breeze condition, compared to other months and sites. Such a phenomenon at SC in October was likely to be mainly caused by the accumulation of O3 and its precursors due to the relatively weak winds under the localized stagnant weather condition rather than the contribution of regional transport from the emission sources in Busan and Ulsan.

The vertical structure and seasonal changes of atmosphere ozone and temperature at Zhongshan Station over East Antarctica

The vertical structure of the atmospheric ozone and temperature as well as the seasonal variations is presented by using ozone sounding data at Zhongshan Station over East Antarctica from February, 2008 to February, 2009. The results show that the heights of thermal tropopause and ozone tropopause are mostly the same with yearly mean 7.9 and 7.4 km separately above the station. There is obvious seasonal variation in the pressure and temperature of the tropopause, manifested by the clear one-wave pattern with an opposite phase. As the turning point of the tropopause temperature is visible in autumn and faint in spring and winter, the tropopause height can be better confirmed by utilization of the changes of ozone. Seasonal variation of the tropospheric ozone of vertical distribution is not clear, relative to stratosphere. In the spring, ozone in the low level of stratosphere lost seriously. The minimum partial ozone in 14 km was 1.57 MPa only and the maximum partial ozone occurred in the up level stratosphere. In the rest of the season the ozone increases with height rising in the low level of stratosphere. The evidence shows that ozone lost in spring is closely related with low temperature of polar night and the process of PSC photochemical destruction ozone in the stratosphere. From the vertical characteristics and seasonal variation of ozone and temperature, it is meaningful to understand formation and development of Antarctic ozone deletion.

Estimation of Ozone Trend in Central Greece, Based on Meteorologically Adjusted Time Series

Data referring to an approximately 8-year period (1999–2007) are analyzed in order to estimate the trend of the daily maximum hourly value of ozone concentration at the east coast of central Greece, where the summer background ozone concentration is high. A Kolmogorov–Zurbenko filter is applied to remove the short-term component from the raw time series of ozone and meteorological variables. Regression models are developed in order to produce meteorologically adjusted ozone time series, involving the noise-free temperature, relative humidity, and wind speed as independent variables. The analysis verifies that the meteorological adjustment provides better results on estimating ozone’s trend, which is found to be increasing (α = 0.001) with an annual rate of 1.34 ± 0.07 μg/m3. This trend could mainly be attributed to policy and changes in the emissions of ozone’s precursors. Additionally, the short-term component of ozone concentration is also meteorologically adjusted and its impact on the trend is examined. The analysis shows that its contribution is of minor importance when the ozone trend is adjusted by temperature, relative humidity, and wind speed. Moreover, the sea breeze circulation system that is frequently developed in the area influences the short-term and seasonal ozone variation, and therefore, it should be taken into account when producing meteorologically adjusted time series. The study’s conclusions could be exploited by environmental and agricultural authorities in order to develop their long-term strategies towards the air quality management.

An atmospheric chemist in search of the tropopause

[1] Delineating the boundary between troposphere and stratosphere in a chemistry transport model requires a state variable for each air mass that maps out the ever shifting, overlapping three-dimensional (3-D) boundary at each time step. Using an artificial tracer, e90, with surface sources and 90 day decay time, the model e90 tropopause matches the 1-D temperature lapse rate definition of the tropopause as well as the seasonal variation of ozone at this boundary. This approach works from equator to pole, over all seasons, unlike methods based on potential vorticity or ozone. By focusing on the time scales that separate stratosphere from troposphere, we examine the cause of ozone seasonality at the midlatitude tropopause, the oldest air in the troposphere (winter descent in the subtropics), and a north-south bias in the age of air of the lowermost stratosphere as evaluated using a northern tracer. The tracer e90 is invaluable in 3-D modeling, readily separating stratosphere from troposphere and a giving quantitative measure of the effective distance from the tropopause.

Measurement of Surface Ozone and its Precursors in Urban and Rural Sites in Beijing

A 4 year time continues measurements of ozone and its precursors including NO, NO2 and CO at an urban and a rural site in Beijing area from January 2005 to December 2008 were analyzed to investigate the seasonal and diurnal variation characters of ozone and its precursors, and to understand the effects of local meteorological conditions. Pronounced seasonal variations of ozone and its precursors were observed in urban area, with the maximum ozone mixing rations appearing in late spring and early summer, minimum appearing in winter. Precursors NO, NO2 and CO show opposite seasonal variation patterns to that of ozone. In rural area, O3, NO and NO2 show similar seasonal variation patterns to that of urban area. While affected by the local natural plants emissions, CO reaches maximum in summer in rural area. Typical polluted cities diurnal variation patterns of ozone and precursors NO, NO2 and CO were observed in urban area, characterized by the peak ozone value appearing at 14:00 and valley during nighttime, precursors showing two peaks related two the morning and evening rushes and reaching valley at ozone peaking time. In rural area, ozone shows similar diurnal pattern, while affected by pollutants transported from upwind urban area, peak value appearing time be delayed by several hours to that of urban area, except in winter. Meteorological conditions, especially boundary layer's changing do primary contribution to the diurnal variation of ozone precursors CO and NO2, with the highest mixing ratios appearing during night time and lowest around noon time in rural area. NO appears single peak in dawn coming from HONO decomposed by the sunlight at rural site.

Study of the seasonal ozone variations at European high latitudes

The geographic area at high latitudes beyond the polar circle is characterized with long darkness during the winter (polar night) and with a long summertime insolation (polar day). Consequentially, the polar vortex is formed and the surrounding strong polar jet is characterized by a strong potential vorticity gradient representing a horizontal transport barrier. The ozone dynamics of the lower and middle stratosphere is controlled both by chemical destruction processes and transport processes. To study the seasonal ozone variation at high latitudes, ozone vertical distributions are examined, collected from the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) (69.3°N, 16.0°E,) station at Andenes and from the stations at Sodankylä (67.4°N, 26.6°E) and at Ny-Ålesund (78.9°N, 11.9°E). The data sets cover the time period from 1994 until 2004. We find a second ozone maximum near 13–15 km, between the tropopause and the absolute ozone maximum near 17–20 km. The maximum is built up by the combination of air mass transport and chemical ozone destruction, mainly caused by the NO x catalytic cycle, which begins after the polar night and intensifies with the increasing day length. Formation of a troposphere inversion layer is observed. The inversion layer is thicker and reaches higher altitudes in winter rather than in summer. However, the temperature inversion during summer is stronger. The formation of an enhanced ozone number density is observed during the spring–summer period. The ozone is accumulated or becomes poor by synoptic weather patterns just above the tropopause from spring to summer. In seasonal average an ozone enhancement above the tropopause is obtained. The stronger temperature inversion during the summer period inhibits the vertical stratosphere–troposphere exchange. The horizontal advection in the upper troposphere and lower stratosphere is enforced during summer. The combination of these mechanisms generates a layer with a very low ozone number density above the troposphere inversion layer subsisting from June/July until the late autumn.

Variations in surface ozone at Nainital: A high‐altitude site in the central Himalayas

Surface ozone measurements have been made for the first time at Nainital (29.37°N, 79.45°E, 1958 m amsl), a high‐altitude site in the central Himalayas, between October 2006 and December 2008. Diurnal variations in ozone do not show the daytime photochemical build‐up typical of urban or rural sites. The seasonal variation shows a distinct ozone maximum in late spring (May; 67.2 ± 14.2 ppbv) with values sometimes exceeding 100 ppbv and a minimum in the summer/monsoon season (August; 24.9 ± 8.4 ppbv). Springtime ozone values in the central Himalayas are significantly higher than those at another high‐altitude site (Mt. Abu) in the western part of India. Seasonal variations in ozone and the processes responsible for the springtime peak are studied using meteorological parameters, insolation, spatial and temporal classifications of air mass trajectories, fire counts, and simulations with a chemical transport model. Net ozone production over the Northern Indian Subcontinent in regionally polluted air masses is estimated to be 3.2 ppbv/day in spring but no clear build‐up is seen at other times of year. Annual average ozone values in regionally polluted air masses (47.1 ± 16.7 ppbv) and on high insolation days (46.8 ± 17.3 ppbv) are similar. Background ozone levels are estimated to be 30–35 ppbv. Regional pollution is shown to have maximum contribution (16.5 ppbv) to ozone levels during May–June and is about 7 ppbv on an annual basis, while the contribution of long‐range transport is greatest during January–March (8–11 ppbv). The modeled stratospheric ozone contribution is 2–16 ppbv. Both the trajectory analysis and the model suggest that the stratospheric contribution is 4–6 ppbv greater than the contribution from regional pollution. Differences in the seasonal variation of ozone over high‐altitude sites in the central Himalayas (Nainital) and western India (Mt. Abu) suggest diverse regional emission sources in India and highlight the large spatial and temporal variability in ozone over the Indian region.

Variation and trend in ozone, UVB radiation and aerosol optical depth at Matrouh, Egypt

Direct Sun observations made by a Brewer spectrophotometer II were used to measure the ozone column (in DU), the ultraviolet radiation in the B region (UVB) (mW m−2 nm−1) and the aerosol optical depth (AOD) (320.1 nm) at Matrouh (31° 20′ N, 27° 13′ E) during the period January 1999 to December 2006. The mean monthly data are used to calculate the seasonal variation and trend in column ozone, UVB and AOD. The study shows that the seasonal variations in the ozone column and damage ultraviolet (DUV) radiation take maximum values in spring (320DU) and summer (105.42mWm−2nm−1) respectively, while the maximum value of AOD (0.14) was found at hot season. The analysis of the mean annual data from 1999–2006 for column ozone, UVB radiation and AOD show positive trends, with values of 0.059, 0.120 and 0.001, respectively.

Potential effects of climate and emissions changes on surface ozone in the Chicago area

Future changes in climate and precursor emissions will likely have important consequences on ground-level ozone concentrations for the City of Chicago and its surrounding suburban/rural areas. Here we use a regional climate–air quality modeling system to evaluate the combined and individual effects of climate warming (and resulting biogenic emissions increases) and anthropogenic emissions perturbations from 1996–2000 to 2048–2052 and 2095–2099 in this region. Two scenarios are considered, including A1FI (higher warming with increasing anthropogenic emissions) and B1 (less warming with reduced anthropogenic emissions). Relative to 1996–2000, projected changes in climate and anthropogenic emissions together lead to little ozone change for the City of Chicago under A1FI but 5.0–7.8 ppb increases under B1 by 2048–2052 and 2095–2099. For A1FI, the decreasing ratio of volatile organic compounds (VOCs) to nitrogen oxides (NOx) reduces ozone concentrations over Chicago, despite the increasing emissions for both NOx and VOCs. Averaged over the Chicago urban and surrounding suburban area, however, surface ozone increase 2.3–7.1 ppb under A1FI by 2095–2099. Additionally, the seasonal ozone variation is projected to increase 84–127% under A1FI but decrease 23–30% under B1 over the Chicago area. By comparison, projected climate warming alone increases the surface ozone by 2.1–8.7 ppb and its seasonal variation by 22–89% over the Chicago area from 1996–2000 to 2095–2099 under both scenarios. Therefore, effective emission regulation and climate considerations are both important to pollution mitigation in the Chicago area.

Seasonal and Diurnal Variations of Ozone near the Mesopause from Observations of the 11.072-GHz Line

Abstract Ground-based observations of the 11.072-GHz line of ozone were made from January 2008 through January 2009. These observations provide an estimate of the diurnal and seasonal variations of ozone in the mesopause region. The 11-GHz line is more sensitive to the ozone at higher altitudes than ground observations of the 142-GHz line, because of the reduced Doppler line width. The observations show an increase in the volume mixing ratio of ozone above 80 km at night by more than a factor of 10 and a seasonal variation of about a factor of 2, which is consistent with the semiannual variations of atomic hydrogen in the mesopause region. The diurnal amplitude and rates of change of the mixing ratios at sunrise and sunset are compared with ground-based observations of the 142-GHz line and the observations of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite, as well as with a simplified chemical model of the creation and destruction of ozone in the mesopause region.

Satellite observations of high nighttime ozone at the equatorial mesopause

Measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument enable the characterization of the seasonal variation of ozone and temperature in the upper mesosphere. These are the first global measurements that resolve both the structure of the secondary ozone maximum at night and the temperature over all seasons of the year. The average nighttime mixing ratios at the altitude of the maximum vary with latitude and season. Analysis shows that the highest mixing ratios are clustered near the equator during equinoxes. The high ozone mixing ratios are observed in exactly the place and time at which the diurnal tide is largest. The diurnal tidal phase is such that coldest temperatures at 95 km occur near midnight. The high ozone is coincident with regions that have both low temperature and low amounts of atomic hydrogen. We focus particularly on ozone mixing ratios in the range of 18–50 ppmv; these occur intermittently in the equinoctial tropics on days when the night temperature is particularly cold. The occurrence of ozone maxima over 20 ppmv was unexpected but is shown in this paper to be consistent with theory and is a result of large‐amplitude diurnal tides. The same seasonal and latitudinal characteristics are seen in ozone density measured by Global Ozone Monitoring by Occultation of Stars.

Mechanisms that influence the formation of high‐ozone regions in the boundary layer downwind of the Asian continent in winter and spring

The seasonal variation of ozone (O3) in the boundary layer (BL) over the western Pacific is investigated using a chemistry‐transport model. The model results for January and April–May 2002 were evaluated by comparison with PEACE aircraft observations. In January, strong northwesterlies efficiently transported NOx from the continent, leading to an O3 increase of approximately 5–10 ppbv over a distance of about 3000 km. In April, southwesterlies dominated due to anticyclone development over the western Pacific. Along this flow, O3 continued to be produced by NOx emitted from East Asia. This resulted in the formation of a high‐O3 (> 50 ppbv) region extending along the coastal areas of East Asia. This seasonal change in O3 was driven in part by a change in the net O3 production rate due to increases in solar UV and H2O. Its exact response depended on the NOx values in the BL. The net O3 production rate increased between winter and spring over the Asian continent and decreased over the remote western Pacific. Model simulations show that about 25% of the total O3 (of 10–20 ppbv) increase over the coastal region of Northeast Asia was due to local production from NOx emissions from China, and the rest was due to changes in background levels as well as emissions from Korea, Japan, and east Siberia. Uplift of BL air over Asia, horizontal transport in the free troposphere, and subsidence were the principal mechanisms of transporting Asian O3 to the central and eastern North Pacific.

Influence of atmospheric ozone, PM 10 and meteorological factors on the concentration of airborne pollen and fungal spores

The increase of allergenic symptoms has been associated with air contaminants such as ozone, particulate matter, pollen and fungal spores. Considering the potential relevance of crossed effects of non-biological pollutants and airborne pollens and fungal spores on allergy worsening, the aim of this work was to evaluate the influence of non-biological pollutants and meteorological parameters on the concentrations of pollen and fungal spores using linear correlations and multiple linear regressions. For that, the seasonal variation of ozone, particulate matter with an equivalent aerodynamic diameter smaller than 10 μm, pollen and fungal spores were assessed and statistical correlations were analysed between those parameters. The data were collected through 2003–2005 in Porto, Portugal. The linear correlations showed that ozone and particulate matter had no significant influence on the concentration of pollen and fungal spores. On the contrary, when using multiple linear regressions those parameters showed to have some influence on the biological pollutants, although results were different depending on the year analysed. Among the meteorological parameters analysed, temperature was the one that most influenced the pollen and fungal spores airborne concentrations, both when using linear and multiple linear correlations. Relative humidity also showed to have some influence on the fungal spore dispersion when multiple linear regressions were used. Nevertheless, the conclusions for each pollen and fungal spore were different depending on the analysed period, which means that the correlations identified as statistically significant may not be, even so, consistent enough. Furthermore, the comparison of the results here presented with those obtained by other authors for only one period should be made carefully.

Evaluation of surface ozone measurements during 2000–2005 at a rural area in the upper Spanish plateau

This paper presents the main experimental results of surface ozone concentrations measured at a rural area in Northern Spain from February 2000 to December 2005. Daily and seasonal variation of ozone has been analysed. The peak concentration levels are obtained in the afternoon, mean value around 88 µg m−3, with extreme average values of 59 µg m−3 in January and 113 µg m−3 in July. Small differences are found in the mean and median of the ozone levels from April to August, when spring and summer maxima are observed. Despite the great inter-annual ozone variability obtained, most air quality indicators showed a positive trend. Further analysis of the monthly mean ozone concentrations of the main percentiles have also been performed using a harmonic model. The upward trend was 6.2 ± 1.7 µg m−3 for the 98th percentile. To interpret the main features of the annual cycle and describe the ozone peaks, the influence of meteorological factors is studied. In summer, ozone production is governed by local processes, air temperature being the major controlling factor. However, the origin of the spring maximum is not so well identified.

Diurnal and seasonal variabilities in surface ozone and its precursor gases at a semi‐arid site Anantapur (14.62°N, 77.65°E, 331 m asl) in India

Measurements of surface ozone and its precursor gases (NOx and CO) have been made at a semi‐arid site Anantapur (14.62°N, 77.65°E, 331 m asl) in tropical Indian region for the period, 2001–2003. NOx and CO levels were the highest during morning and late night hours at this site. Diurnal variations of ozone concentrations varied from 25 ppbv to 50 ppbv and were observed to increase gradually after sunrise, attaining a maximum value by the evening and decreasing gradually thereafter. During monsoon months, the diurnal amplitude of ozone was found to be small (20–25 ppbv). Seasonal variation in ozone showed a pronounced maximum (40–50 ppbv) in the winter and summer. Local pollutants were major contributors to the ozone levels during this period. Ozone shows a yearly mean mixing ratio of about 35.9 ± 8.8 ppbv. The daytime concentration of CO and NOx varied between 200 to 1200 ppbv and 3 to 20 ppbv respectively for the period studied. Annual average mixing ratios of oxides of nitrogen (NOx) and CO were observed to be 3.9±0.6 ppbv and 436±64 ppbv, respectively.

Monthly and Seasonal Variation of Ozone over the Kingdom of Saudi Arabia and Surrounding Area

Monthly and Seasonal Variation of Ozone over the Kingdom of Saudi Arabia and Surrounding Area

Analysis of the seasonal variation of ozone in the boundary layer in East Asia using the Community Multi-scale Air Quality model: What controls surface ozone levels over Japan?

Ozone (O 3) concentrations in East Asia were simulated using the Community Multi-scale Air Quality model and their reproducibility was confirmed by comparing with observation data at Japanese monitoring sites. The model can reproduce the seasonal variation of surface O 3 over Japan. In particular, for the southern parts of Japan, simulated surface O 3 concentrations are strongly correlated with observations. Surface O 3 distribution over East Asia varies dynamically from season to season according to the meteorological condition. In May and June, 2-month average O 3 concentrations in the boundary layer are highest, 55–70 ppbv over East China and Japan at 35–40°N. We estimated the seasonal variation of the contribution of chemically produced O 3 by east Asian regional emissions. In the summertime, the contribution of the regional Asian emissions to O 3 concentrations is around 40–70% over most of China, and the highest is 60–70% (<35 ppbv) at the mouth area of Yantze River. This suggests that O 3 concentrations over East Asia are strongly influenced by the chemical production by regional emissions during summer season. However, the inflow from outside of this model domain also contributes substantial O 3 concentration over East Asia and its contribution is predominant in winter and early spring. The seasonal change of O 3 concentrations over Japan is characterized by two peaks in spring and autumn and summer minimum. The spring peak event in 2002 consists of split peaks: the first peak in Mar–Apr is mainly influenced by the inflow from outside of this model domain, the second spring peak between May and June is mainly influenced by chemically produced O 3 by regional emissions. During the summer season, O 3 concentrations are the lowest over year because of the weak Asian outflow and northward penetration of the marine air mass.