Quantify the regional methane emissions based on a new SCIAMACHY data set

2020 ◽  
Author(s):  
Mengyao Liu ◽  
Ronald Van der A ◽  
Haiyue Tan ◽  
Christian Frankenberg ◽  
Ilse Aben ◽  
...  
Keyword(s):  
Eastern China ◽  
Global Ocean ◽  
Background Concentration ◽  
Mountain Areas ◽  
Data Set ◽  
Cloud Data ◽  
Mixing Ratios ◽  
Regional Sources ◽  
Surface Measurements

<p>Methane (CH4) is the most important anthropogenic greenhouse gas after carbon dioxide, and it keeps increasing globally since 2007 after a period of relative stability, which is well-documented by surface measurements and satellites. Although satellites provide long-term global observations of CH4, the interpretation of column-averaged mixing ratios (xCH4) is difficult due to the influence of elevated terrains (i.e. mountain areas) and less abundant methane in the stratosphere. The lack of data over the ocean further limits global insights. Here we build a long-term global CH4 data set at a resolution of 0.25° × 0.25°  from SCIAMACHY, including the areas over the ocean, with the help of FRESCO cloud data. We dynamically consider the influence of elevations and contributions from the stratosphere through converting xCH4 to tropospheric xCH4 (trop_xCH4) by applying the daily ratios of tropospheric to stratospheric xCH4 in GEOS-Chem model.</p><p>The large increases occur in Trop_xCH4 over the source regions and mountain areas. The trend of SCIAMACHY Trop_xCH4 over the global ocean is comparable to the trend of NOAA globally averaged marine monthly mean data, showing the capability of SCIAMACHY in monitoring the ocean. After removing the latitudinally independent background concentration based on SCIAMACHY data over the ocean, we quantify the regional sources. A significant trend in Trop_ xCH4 relating to the background in Eastern China, India, tropical Africa, and tropical South America is further found from 2003 to 2011. </p>

scholarly journals Ozone response to emission reductions in the southeastern United States

2018 ◽  
Vol 18 (11) ◽  
pp. 8183-8202 ◽  
Author(s):  
Charles L. Blanchard ◽  
George M. Hidy
Keyword(s):  
Environmental Protection Agency ◽  
Study Data ◽  
Nox Emissions ◽  
Emission Rates ◽  
Emission Reductions ◽  
Mixing Ratios ◽  
Southeastern Us ◽  
Surface Measurements ◽  
Nitrate Deposition

Abstract. Ozone (O3) formation in the southeastern US is studied in relation to nitrogen oxide (NOx) emissions using long-term (1990s–2015) surface measurements of the Southeastern Aerosol Research and Characterization (SEARCH) network, U.S. Environmental Protection Agency (EPA) O3 measurements, and EPA Clean Air Status and Trends Network (CASTNET) nitrate deposition data. Annual fourth-highest daily peak 8 h O3 mixing ratios at EPA monitoring sites in Georgia, Alabama, and Mississippi exhibit statistically significant (p < 0.0001) linear correlations with annual NOx emissions in those states between 1996 and 2015. The annual fourth-highest daily peak 8 h O3 mixing ratios declined toward values of ∼ 45–50 ppbv and monthly O3 maxima decreased at rates averaging ∼ 1–1.5 ppbv yr−1. Mean annual total oxidized nitrogen (NOy) mixing ratios at SEARCH sites declined in proportion to NOx emission reductions. CASTNET data show declining wet and dry nitrate deposition since the late 1990s, with total (wet plus dry) nitrate deposition fluxes decreasing linearly in proportion to reductions of NOx emissions by ∼ 60 % in Alabama and Georgia. Annual nitrate deposition rates at Georgia and Alabama CASTNET sites correspond to 30 % of Georgia emission rates and 36 % of Alabama emission rates, respectively. The fraction of NOx emissions lost to deposition has not changed. SEARCH and CASTNET sites exhibit downward trends in mean annual nitric acid (HNO3) concentrations. Observed relationships of O3 to NOz (NOy–NOx) support past model predictions of increases in cycling of NO and increasing responsiveness of O3 to NOx. The study data provide a long-term record that can be used to examine the accuracy of process relationships embedded in modeling efforts. Quantifying observed O3 trends and relating them to reductions in ambient NOy species concentrations offers key insights into processes of general relevance to air quality management and provides important information supporting strategies for reducing O3 mixing ratios.

scholarly journals Long-term NO<sub>x</sub> measurements in the remote marine tropical troposphere

2020 ◽  
Author(s):  
Simone T. Andersen ◽  
Lucy J. Carpenter ◽  
Beth S. Nelson ◽  
Luis Neves ◽  
Katie A. Read ◽  
...  
Keyword(s):  
Time Series ◽  
Light Emitting Diode ◽  
Ultra Violet ◽  
Data Set ◽  
Light Emitting ◽  
Mixing Ratios ◽  
Remote Troposphere ◽  
Tropical Troposphere ◽  
Term Data

Abstract. Atmospheric nitrogen oxides (NO + NO2 = NOx) have been measured at the Cape Verde Atmospheric Observatory (CVAO) in the tropical Atlantic (16° 51' N, 24° 52' W) since October 2006. These measurements represent a unique time series of NOx in the background remote troposphere. Nitrogen dioxide (NO2) is measured via photolytic conversion to nitric oxide (NO) by ultra violet light emitting diode arrays followed by chemiluminescence detection. Since the measurements began, a blue light converter (BLC) has been used for NO2 photolysis, with a maximum spectral output of 395 nm from 2006–2015 and of 385 nm from 2015. The original BLC used was constructed with a Teflon-like material and appeared to cause an overestimation of NO2 when illuminated. To avoid such interferences, a new additional photolytic converter (PLC) with a quartz photolysis cell (maximum spectral output also 385 nm) was implemented in March 2017. Once corrections are made for the NO2 artefact from the original BLC, the two NO2 converters are shown to give comparable NO2 mixing ratios (PLC = 0.92 × BLC, R2 = 0.92), giving confidence in the quantitative measurement of NOx at very low levels. Data analysis methods for the NOx measurements made at CVAO have been developed and applied to the entire time series to produce an internally consistent and high quality long-term data set. NO has a clear diurnal pattern with a maximum mixing ratio of 2–10 pptV during the day depending on the season and ~0 pptV during the night. NO2 shows a fairly flat diurnal signal, although a small increase in daytime NOx is evident in some months. Monthly average mixing ratios of NO2 vary between 5 and 30 pptV depending on the season. Clear seasonal trends in NO and NO2 levels can be observed with a maximum in autumn/winter and a minimum in spring/summer.

scholarly journals Long-term study of VOCs measured with PTR-MS at a rural site in New Hampshire with urban influences

2009 ◽  
Vol 9 (1) ◽  
pp. 4251-4299
Author(s):  
C. Jordan ◽  
E. Fitz ◽  
T. Hagan ◽  
B. Sive ◽  
E. Frinak ◽  
...  
Keyword(s):  
Dimethyl Sulfide ◽  
Proton Transfer Reaction ◽  
Early Morning ◽  
Rural Site ◽  
High Time Resolution ◽  
Data Set ◽  
Mixing Ratios ◽  
Long Term Study ◽  
Urban Rural

Abstract. A long-term, high time-resolution volatile organic compound (VOC) data set from a ground site that experiences urban, rural, and marine influences in the northeastern United States is presented. A proton-transfer-reaction mass spectrometer (PTR-MS) was used to quantify 15 VOCs: a marine tracer dimethyl sulfide (DMS), a biomass burning tracer acetonitrile, biogenic compounds (monoterpenes, isoprene), oxygenated VOCs (OVOCs: methyl vinyl ketone (MVK) plus methacrolein (MACR), methanol, acetone, methyl ethyl ketone (MEK), acetaldehyde, and acetic acid), and aromatic compounds (benzene, toluene, C8 and C9 aromatics). Time series, overall and seasonal medians, with 10th and 90th percentiles, seasonal mean diurnal profiles, and inter-annual comparisons of mean summer and winter diurnal profiles are shown. Methanol and acetone exhibit the highest overall median mixing ratios 1.44 and 1.02 ppbv, respectively. Comparing the mean diurnal profiles of less well understood compounds (e.g., MEK) with better known compounds (e.g., isoprene, monoterpenes, and MVK+MACR) that undergo various controls on their atmospheric mixing ratios provides insight into possible sources of the lesser known compounds. The constant diurnal value of ≈0.7 for the toluene:benzene ratio in winter, may possibly indicate the influence of wood-based heating systems in this region. Methanol exhibits an initial early morning release in summer unlike any other OVOC (or isoprene) and a dramatic late afternoon mixing ratio increase in spring. Although several of the OVOCs appear to have biogenic sources, differences in features observed between isoprene, methanol, acetone, acetaldehyde, and MEK suggest they are produced or emitted in unique ways.

scholarly journals Ozone Response to Emission Reductions in the Southeastern United States

2017 ◽  
Author(s):  
Charles L. Blanchard ◽  
George M. Hidy
Keyword(s):  
Environmental Protection Agency ◽  
Nox Emissions ◽  
Emission Rates ◽  
Emission Reductions ◽  
Mixing Ratios ◽  
Surface Measurements ◽  
Clean Air ◽  
Annual Total ◽  
Nitrate Deposition

Abstract. Ozone (O3) formation in the southeastern U.S. is studied in relation to nitrogen oxide (NOx) emissions using long-term (1990s–2015) surface measurements of the Southeastern Aerosol Research and Characterization (SEARCH) network, U.S. Environmental Protection Agency (EPA) O3 measurements, and EPA Clean Air Status and Trends Network (CASTNet) nitrate deposition data. CASTNet data show declining wet and dry nitrate deposition since the late 1990s, with total (wet plus dry) nitrate deposition fluxes decreasing linearly in proportion to reductions of NOx emissions in in Alabama and Georgia. Annual nitrate deposition rates at Georgia and Alabama CastNet sites correspond to 30 % of Georgia emission rates and 36 % of Alabama emission rates, respectively. The fraction of NOx emissions lost to deposition has not changed over time. SEARCH and EPA CASTNet sites exhibit comparable downward trends in mean annual nitric acid (HNO3) concentrations. Mean annual total oxidized nitrogen (NOy) mixing ratios at SEARCH sites declined in proportion to NOx emission reductions. Annual 4th-highest daily peak 8-hour O3 mixing ratios at EPA monitoring sites in Georgia, Alabama, and Mississippi exhibit statistically-significant (p 

scholarly journals Global distribution of Earth’s surface shortwave radiation budget

2005 ◽  
Vol 5 (4) ◽  
pp. 4545-4597 ◽  
Author(s):  
N. Hatzianastassiou ◽  
C. Matsoukas ◽  
A. Fotiadi ◽  
K. G. Pavlakis ◽  
E. Drakakis ◽  
...  
Keyword(s):  
Radiative Heating ◽  
Surface Radiation ◽  
Radiation Budget ◽  
Shortwave Radiation ◽  
Physical Parameters ◽  
Transfer Model ◽  
Data Set ◽  
Surface Measurements ◽  
Global Mean

Abstract. The monthly mean shortwave (SW) radiation budget at the Earth's surface (SRB) was computed on 2.5-degree longitude-latitude resolution for the 17-year period from 1984 to 2000, using a radiative transfer model accounting for the key physical parameters that determine the surface SRB, and long-term climatological data from the International Satellite Cloud Climatology Project (ISCCP-D2). The model input data were supplemented by data from the National Centers for Environmental Prediction – National Center for Atmospheric Research (NCEP-NCAR) and European Center for Medium Range Weather Forecasts (ECMWF) Global Reanalysis projects, and other global data bases such as TIROS Operational Vertical Sounder (TOVS) and Global Aerosol Data Set (GADS). The model surface radiative fluxes were validated against surface measurements from 22 stations of the Baseline Surface Radiation Network (BSRN) covering the years 1992–2000, and from 700 stations of the Global Energy Balance Archive (GEBA), covering the period 1984–2000. The model is in very good agreement with BSRN and GEBA, with a negative bias of 14 and 6.5 Wm-2, respectively. The model is able to reproduce interesting features of the seasonal and geographical variation of the surface SW fluxes at global scale, which is not possible with surface measurements. Based on the 17-year average model results, the global mean SW downward surface radiation (DSR) is equal to 171.6 Wm−2, whereas the net downward (or absorbed) surface SW radiation is equal to 149.4 Wm−2, values that correspond to 50.2 and 43.7% of the incoming SW radiation at the top of the Earth's atmosphere. These values involve a long-term surface albedo equal to 12.9%. Significant increasing trends in DSR and net DSR fluxes were found, equal to 4.1 and 3.7 Wm−2, respectively, over the 1984–2000 period (equivalent to 2.4 and 2.2 Wm−2 per decade), indicating an increasing surface solar radiative heating. This surface SW radiative heating is primarily attributed to clouds, especially low-level, and secondarily to other parameters such as total precipitable water. The surface solar heating occurs mainly in the period starting from the early 1990s, in contrast to the commonly reported decreasing trend in DSR through the late 1980s, found also in our study. The computed global mean DSR and net DSR flux anomalies were found to range within ±8 and ±6 Wm−2, respectively, with signals from El Niño and La Niña events, and the Pinatubo eruption, whereas significant positive anomalies have occurred in the period 1992–2000.

Investigating stratospheric circulation and chemistry changes over three decades with trace gas data from aircraft, large balloons, and AirCores

2021 ◽  
Author(s):  
Johannes Laube ◽  
Elliot Atlas ◽  
Karina Adcock ◽  
Elise Droste ◽  
Pauli Heikkinen ◽  
...  
Keyword(s):  
Chem Phys ◽  
Trace Gas ◽  
Data Set ◽  
Stratospheric Chemistry ◽  
Air Samples ◽  
Mixing Ratios ◽  
Transit Times ◽  
Long Term Trends ◽  
Stratospheric Circulation

&lt;p&gt;Laube et al. (2020) investigated stratospheric changes between 2009 and 2018 with halogenated trace gas data (CFC-11, CFC-12, H-1211, H-1301, HCFC-22, and SF&lt;sub&gt;6&lt;/sub&gt;) from air samples collected via aircraft and AirCores, and compared the mixing ratios and average stratospheric transit times derived from these observations with those from a global model. We here expand this analysis in three ways: firstly, by adding data from further traces gases such as CFC-115, C&lt;sub&gt;2&lt;/sub&gt;F&lt;sub&gt;6&lt;/sub&gt;, and HCFC-142b to broaden the range of tropospheric trends and stratospheric lifetimes, both of which help to assess the robustness of inferred long-term trends in the stratosphere; secondly, by increasing the temporal span of the observations to nearly three decades using new AirCore observations as well as reanalysed archived air samples collected on board high altitude aircraft and large balloons in the 1990s and 2000s; and thirdly, by investigating the fractional release factors and mean ages of air derived from the aforementioned species as measures of their stratospheric chemistry and the strength of the Brewer-Dobson circulation. In combination with model data from the Chemical Langrangian Model of the Stratosphere (CLaMS) this unique data set allows for an unprecedented evaluation of stratospheric chemistry and dynamics in the mid-latitudes of the Northern Hemisphere.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;em&gt;References&lt;/em&gt;&lt;/p&gt;&lt;p&gt;Laube, &lt;em&gt;et al.&lt;/em&gt;, Atmos. Chem. Phys., 20, 9771&amp;#8211;9782, 2020, https://doi.org/10.5194/acp-20-9771-2020&lt;/p&gt;

scholarly journals Long-term trends of surface ozone and its influencing factors at the Mt Waliguan GAW station, China – Part 2: The roles of anthropogenic emissions and climate variability

2018 ◽  
Vol 18 (2) ◽  
pp. 773-798 ◽  
Author(s):  
Wanyun Xu ◽  
Xiaobin Xu ◽  
Meiyun Lin ◽  
Weili Lin ◽  
David Tarasick ◽  
...  
Keyword(s):  
Trajectory Analysis ◽  
Surface Ozone ◽  
Eastern China ◽  
Sunspot Cycle ◽  
Anthropogenic Emissions ◽  
South East Asia ◽  
Data Set ◽  
Air Masses ◽  
Long Term Trends

Abstract. Inter-annual variability and long-term trends in tropospheric ozone are both environmental and climate concerns. Ozone measured at Mt Waliguan Observatory (WLG, 3816 m a.s.l.) on the Tibetan Plateau over the period of 1994–2013 has increased significantly by 0.2–0.3 ppbv yr−1 during spring and autumn but shows a much smaller trend in winter and no significant trend in summer. Here we explore the factors driving the observed ozone changes at WLG using backward trajectory analysis, chemistry–climate model hindcast simulations (GFDL AM3), a trajectory-mapped ozonesonde data set, and several climate indices. A stratospheric ozone tracer implemented in GFDL AM3 indicates that stratosphere-to-troposphere transport (STT) can explain ∼ 60 % of the simulated springtime ozone increase at WLG, consistent with an increase in the NW air-mass frequency inferred from the trajectory analysis. Enhanced STT associated with the strengthening of the mid-latitude jet stream contributes to the observed high ozone anomalies at WLG during the springs of 1999 and 2012. During autumn, observations at WLG are more heavily influenced by polluted air masses originating from South East Asia than in the other seasons. Rising Asian anthropogenic emissions of ozone precursors are the key driver of increasing autumnal ozone observed at WLG, as supported by the GFDL AM3 model with time-varying emissions, which captures the observed ozone increase (0.26 ± 0.11 ppbv yr−1). AM3 simulates a greater ozone increase of 0.38 ± 0.11 ppbv yr−1 at WLG in autumn under conditions with strong transport from South East Asia and shows no significant ozone trend in autumn when anthropogenic emissions are held constant in time. During summer, WLG is mostly influenced by easterly air masses, but these trajectories do not extend to the polluted regions of eastern China and have decreased significantly over the last 2 decades, which likely explains why summertime ozone measured at WLG shows no significant trend despite ozone increases in eastern China. Analysis of the Trajectory-mapped Ozonesonde data set for the Stratosphere and Troposphere (TOST) and trajectory residence time reveals increases in direct ozone transport from the eastern sector during autumn, which adds to the autumnal ozone increase. We further examine the links of ozone variability at WLG to the quasi-biennial oscillation (QBO), the East Asian summer monsoon (EASM), and the sunspot cycle. Our results suggest that the 2–3-, 3–7-, and 11-year periodicities are linked to the QBO, EASM index, and sunspot cycle, respectively. A multivariate regression analysis is performed to quantify the relative contributions of various factors to surface ozone concentrations at WLG. Through an observational and modelling analysis, this study demonstrates the complex relationships between surface ozone at remote locations and its dynamical and chemical influencing factors.

scholarly journals Long-term study of VOCs measured with PTR-MS at a rural site in New Hampshire with urban influences

2009 ◽  
Vol 9 (14) ◽  
pp. 4677-4697 ◽  
Author(s):  
C. Jordan ◽  
E. Fitz ◽  
T. Hagan ◽  
B. Sive ◽  
E. Frinak ◽  
...  
Keyword(s):  
Dimethyl Sulfide ◽  
Proton Transfer Reaction ◽  
Early Morning ◽  
Rural Site ◽  
High Time Resolution ◽  
Data Set ◽  
Mixing Ratios ◽  
Long Term Study ◽  
Urban Rural

Abstract. A long-term, high time-resolution volatile organic compound (VOC) data set from a ground site that experiences urban, rural, and marine influences in the Northeastern United States is presented. A proton-transfer-reaction mass spectrometer (PTR-MS) was used to quantify 15 VOCs: a marine tracer dimethyl sulfide (DMS), a biomass burning tracer acetonitrile, biogenic compounds (monoterpenes, isoprene), oxygenated VOCs (OVOCs: methyl vinyl ketone (MVK) plus methacrolein (MACR), methanol, acetone, methyl ethyl ketone (MEK), acetaldehyde, and acetic acid), and aromatic compounds (benzene, toluene, C8 and C9 aromatics). Time series, overall and seasonal medians, with 10th and 90th percentiles, seasonal mean diurnal profiles, and inter-annual comparisons of mean summer and winter diurnal profiles are shown. Methanol and acetone exhibit the highest overall median mixing ratios 1.44 and 1.02 ppbv, respectively. Comparing the mean diurnal profiles of less well understood compounds (e.g., MEK) with better known compounds (e.g., isoprene, monoterpenes, and MVK + MACR) that undergo various controls on their atmospheric mixing ratios provides insight into possible sources of the lesser known compounds. The constant diurnal value of ~0.7 for the toluene:benzene ratio in winter, may possibly indicate the influence of wood-based heating systems in this region. Methanol exhibits an initial early morning release in summer unlike any other OVOC (or isoprene) and a dramatic late afternoon mixing ratio increase in spring. Although several of the OVOCs appear to have biogenic sources, differences in features observed between isoprene, methanol, acetone, acetaldehyde, and MEK suggest they are produced or emitted in unique ways.

scholarly journals Long-term NO<sub><i>x</i></sub> measurements in the remote marine tropical troposphere

2021 ◽  
Vol 14 (4) ◽  
pp. 3071-3085
Author(s):  
Simone T. Andersen ◽  
Lucy J. Carpenter ◽  
Beth S. Nelson ◽  
Luis Neves ◽  
Katie A. Read ◽  
...  
Keyword(s):  
Time Series ◽  
Light Emitting Diode ◽  
Least Squares Regression ◽  
Data Set ◽  
Light Emitting ◽  
Mixing Ratios ◽  
Remote Troposphere ◽  
Tropical Troposphere ◽  
Autumn And Winter

Abstract. Atmospheric nitrogen oxides (NO + NO2 = NOx) have been measured at the Cape Verde Atmospheric Observatory (CVAO) in the tropical Atlantic (16∘51′ N, 24∘52′ W) since October 2006. These measurements represent a unique time series of NOx in the background remote troposphere. Nitrogen dioxide (NO2) is measured via photolytic conversion to nitric oxide (NO) by ultraviolet light-emitting diode arrays followed by chemiluminescence detection. Since the measurements began, a blue light converter (BLC) has been used for NO2 photolysis, with a maximum spectral output of 395 nm from 2006 to 2015 and of 385 nm from 2015 onwards. The original BLC used was constructed with a Teflon-like material and appeared to cause an overestimation of NO2 when illuminated. To avoid such interferences, a new additional photolytic converter (PLC) with a quartz photolysis cell (maximum spectral output also 385 nm) was implemented in March 2017. Once corrections are made for the NO2 artefact from the original BLC, the two NO2 converters are shown to give comparable NO2 mixing ratios (BLC = 0.99 × PLC + 0.7 ppt, linear least-squares regression), giving confidence in the quantitative measurement of NOx at very low levels. Data analysis methods for the NOx measurements made at CVAO have been developed and applied to the entire time series to produce an internally consistent and high-quality long-term data set. NO has a clear diurnal pattern with a maximum mixing ratio of 2–10 ppt during the day depending on the season and ∼ 0 ppt during the night. NO2 shows a fairly flat diurnal signal, although a small increase in daytime NOx is evident in some months. Monthly average mixing ratios of NO2 vary between 5 and 30 ppt depending on the season. Clear seasonal trends in NO and NO2 levels can be observed with a maximum in autumn and winter and a minimum in spring and summer.

scholarly journals Bromocarbons in the tropical marine boundary layer at the Cape Verde Observatory – measurements and modelling

2009 ◽  
Vol 9 (22) ◽  
pp. 9083-9099 ◽  
Author(s):  
L. M. O'Brien ◽  
N. R. P. Harris ◽  
A. D. Robinson ◽  
B. Gostlow ◽  
N. Warwick ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Transport Model ◽  
Cape Verde ◽  
Background Concentration ◽  
Emission Rates ◽  
Chemical Transport Model ◽  
Model Studies ◽  
Mixing Ratios ◽  
Measurement Period

Abstract. A new gas chromatograph was used to make measurements of halocarbons at the Cape Verde observatory during late May and early June 2007. The instrument demonstrated its potential for long-term autonomous measurements. Bromoform (CHBr3) exhibits the most variability of all the halocarbons observed, ranging from a background concentration of about 4 ppt to a maximum of >40 ppt during the course of the measurement period. CH2Br2 correlates well with bromoform, suggesting a common regional source. Methyl iodide does not correlate with these bromocarbons, with base levels of around 1–2 ppt and some periods of much higher mixing ratios. Using published bromocarbon emission rates, our chemical transport model studies, presented here, do not reproduce the observations. Local emission magnitudes and CHBr3:CH2Br2 ratios must be increased more in line with the recent observations of Yokouchi et al. (2005) to improve the model to measurement comparison. Even when the model reproduces the observed bromocarbons, modelled BrO is much less than recent tropical observations (Read et al., 2008). A sea salt source seems the likely explanation. When high BrO is reproduced, the model agrees much better with the observed ozone changes, including diurnal variation, during the measurement period but it is suggested that a representation of iodine chemistry in the model is also required.

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