Summer Smog Episode Research Articles

Hydrogen peroxide, organic peroxides, carbonyl compounds, and organic acids measured at Pabstthum during BERLIOZ

Gas‐phase H2O2, organic peroxides, carbonyl compounds, and carboxylic acids were measured from mid‐July to early August 1998 during the Berlin ozone (BERLIOZ) campaign in Pabstthum, Germany. The rural site, located 50 km northwest from Berlin, was chosen to measure the pollutants downwind during a summer smog episode. The hydroperoxides showed pronounced diurnal variations with peak mixing ratios in the early afternoon. The maximum mixing ratios were 1.4 ppbv (H2O2), 0.64 ppbv (methylhydroperoxide), and 0.22 ppbv (hydroxymethyl‐hydroperoxide). H2O2 was formed through photochemical activity, but originated also from vertical transport from air residing above the local inversion layer in the morning hours. Sometimes a second maximum was observed in the late afternoon‐evening: This H2O2 might be formed from ozonolysis of biogenic alkenes. Ratios of H2O2/HNO3 were used as indicators for the determination of NOx‐sensitive versus volatile organic compound (VOC)‐sensitive regimes for photochemical production of ozone. Diurnal profiles were measured for alkanals (C2–C10), showing maximum mixing ratios decreased from C2 (0.6 ppbv) to C5 (0.1 ppbv) alkanals, which originate primarily from anthropogenic hydrocarbon degradation processes. However, higher C6, C9, and C10 alkanals show strong fluctuations (0.25, 0.17, and 0.13 ppbv, respectively), showing evidence of biogenic emissions. Both primary unsaturated carbonyl (methyl vinyl ketone, methacrolein) and secondary oxidation products of isoprene (hydroxyacetone and glycolaldehyde, up to 0.16 and 0.20 ppbv, respectively) showed excellent correlation. Diurnal profiles of glyoxal, methylglyoxal, biacetyl, benzaldehyde, and pinonaldehyde were also obtained. Formaldehyde was measured continuously by long‐path DOAS and by an instrument based on the “Hantzsch” reaction; however, mixing ratios measured by DOAS (maximum 7.7 ppbv) were systematically larger by a factor of 1.3 on average, but by a factor of 1.7 during high photochemical activity. Homologous series of monocarboxylic acids were determined: Formic and acetic acid varied between 0.6 and 3.0 ppbv. The mixing ratio of the other dropped from 0.1 to 0.2 ppbv for C3 to typical 0.01 to 0.03 ppbv for C6, and from 0.01 to 0.002 ppbv for C7 to C9 monocarboxylic acids.

Analysis of a summer smog episode in the Berlin-Brandenburg region with a nested atmosphere -- chemistry model

Abstract. An analysis of a pollution episode in an urban atmosphere, using a complex model system is presented. The nested atmosphere-chemistry model system simulates the atmospheric conditions during a one week measurement campaign, called FLUMOB, in July 1994 in Berlin-Brandenburg, Germany. The analysis shows that naturally emitted hydrocarbons played the dominant role in the ozone formation in the investigated area. The composition of non-methane volatile organic compounds was made up to 70--80% by biogenically emitted hydrocarbons. During the analysed case, ozone formation was sensitive to hydrocarbon concentrations so that the ozone production was limited by the availability of hydrocarbons and thus especially by the amount which was biogenically emitted. Furthermore, it is shown that the FLUMOB episode was influenced by elevated concentrations of ozone in the free troposphere. In contrast to previous analyses, the importance of ozone produced outside of Europe is emphasized. In spite of the stagnant high pressure situation which occurred during the FLUMOB episode Germany was significantly influenced by long-range transport of ozone. This transport also influenced near surface ozone concentrations.

Reformulated and alternative fuels: modeled impacts on regional air quality with special emphasis on surface ozone concentration.

The comprehensive European Air Pollution and Dispersion model system was used to estimate the impacts of the usage of reformulated and alternative fuels on regional air quality with special emphasis on surface ozone concentrations. A severe western European summer smog episode in July 1994 has been used as a reference, and the model predictions have been evaluated for this episode. A forecast simulation for the year 2005 (TREND) has been performed, including the future emission development based on the current legislation and technologies available. The results of the scenario TREND are used as a baseline for the other 2005 fuel scenarios, including fuel reformulation, fuel sulfur content, and compressed natural gas (CNG) as an alternative fuel. Compared to the year 1994, significant reductions in episode peak ozone concentrations and ozone grid hours are predicted for the TREND scenario. These reductions are even more pronounced within the investigated alternative and reformulated fuel scenarios. Especially, low sulfur fuels are appropriate for an immediate improvement in air quality, because they effect the emissions of the whole fleet. Furthermore, the simulation results indicate that the introduction of CNG vehicles would also enhance air quality with respect to ozone.

Assessing the meteorological conditions of a deep Italian Alpine valley system by means of a measuring campaign and simulations with two models during a summer smog episode

The typical features of a summer smog episode in the highly complex terrain of the Province of Bolzano (Northern Italy) were investigated by numerical modelling with two non-hydrostatic models, ground-based monitoring stations, and vertical profiling with two sodars and an ultra-light aircraft. High ozone concentrations are most likely to appear in situations where the local circulation in the valleys is decoupled from the synoptic flow above during anticyclonic weather regimes. Both models (MM5 and TVM) produced similar results and were able to simulate the local winds in the valleys. A comparison of the measured data to the model simulation results made an evaluation of the performance of the two models in such complex terrain possible. Both models proved to be suitable for the simulation of the meteorological conditions during such summer smog episodes in complex terrain.

The loss of NO2, HNO3, NO3/N2O5, and HO2/HOONO2 on soot aerosol: A chamber and modeling study

The heterogeneous loss of NO2, HNO3, NO3/N2O5, and HO2/HO2NO2 on soot aerosol was investigated in a large aerosol chamber for interaction times of up to several days. By fitting a detailed model to the measured time profiles of the trace gas concentrations in the presence / absence of soot aerosol, the following reaction probabilities have been deduced at 294 K and < 10 ppm H2O (in parentheses: at 50% r.h.):γ(NO2) ≤ 4× 10−8; γ(HNO3→NO2) ≤ 3× 10−7; γ(NO3) ≤ 3 × 10−4 (≤10−3); γ(N2O5, hydrolysis)=(4±2) ×10−5 ((2±1 ) × 10−4); γ(N2O5, reduction)=(4±2) × 10−6; γ(HO2≤ 10−2; γ(HO2NO2) ≤ 10−5. These results were adopted in a series of box model calculations for four‐day summer smog episodes, probing a wide range of NO emission rates. The 2nd day ozone maxima were reduced up to 10% in the presence of 20 µg m−3 soot aerosol, mainly due to the heterogeneous loss of HO2.

Modelling of summer photochemical smog in the prague region

Numerical model for simulation and evaluation of summer episodes of anthropogenic surface ozone (summer smog episodes) is presented in this article. This model has been used for special air-pollution studies in the region of Prague (central part of Bohemia - the Czech Republic). It is based on so called “puff model” technology and lagrangian method of trajectories construction in the boundary layer of atmosphere is applied. Processes of turbulent dispersion of puffs, photochemical and other chemical transformations and deposition of compounds on the earth surface are also taken into account. System of equations used for chemistry description of the model is presented here in details and a brief informative presentation of model results is also included.

Photochemical smog modelling in Prague

A model for simulation and evaluation of summer episodes of anthropogenic surface ozone (summer smog episodes) is presented in this paper. This model has been used for air-pollution studies in the region of Prague (central part of Bohemia, the Czech Republic). It is based on so-called "puff model" technology and the Lagrangian method of trajectory construction in the boundary layer of the atmosphere is applied. Processes of turbulent dispersion of puffs, photochemical and other chemical transformations and deposition of compounds on the Earth"s surface are also taken into account. A brief informative presentation of model results is included.

Numerical modelling of regional scale transport and photochemistry directly together with meteorological processes

A three-dimensional regional scale atmosphere-chemistry model has been developed to contribute to an improved understanding of atmospheric photochemical processes. This on-line model determines meteorological processes directly together with tracer transport and photochemistry. Usually, off-line chemistry-transport models are applied which use archived data from a meteorological model as input information. However, a number of disadvantages result from the seperation of meteorological and photochemical modelling: only a part of the whole meteorological information is available in the sampled data sets and only in distinct time intervals. The availability of the whole meteorological information including subgrid scale dynamical motions like turbulence and moist convection at every model time step is the main advantage of the on-line procedure. In addition, on-line modelling allows to consider chemical–dynamical feedbacks which is not possible in the off-line mode. For validation and evaluation studies a 10-days simulation of a summersmog episode over Europe in July 1994 has been carried out with the first version of the on-line model. The results are compared with observations and with an off-line model simulation. The on-line model is able to reproduce measured near-surface concentrations in much better agreement than the off-line model does. The reason is an improved representation of tracer transport in convective clouds in the on-line model. It is responsible for the upward mixing of short-living precursor substances of photooxidants from the planetary boundary layer into the free troposphere, with a significant impact on photooxidants concentrations in the planetary boundary layer as well as in the free troposphere.

Gas/Particle Partitioning of Semivolatile Organic Compounds To Model Inorganic, Organic, and Ambient Smog Aerosols

Gas/particle (G/P) partitioning is an important process that affects the deposition, chemical reactions, long-range transport, and impact on human and ecosystem health of atmospheric semivolatile organic compounds (SOCs). Gas/particle partitioning coefficients (Kp) were measured in an outdoor chamber for a group of polynuclear aromatic hydrocarbons (PAHs) and n-alkanes sorbing to three types of model aerosol materials: solid ammonium sulfate, liquid dioctyl phthalate (DOP), and secondary organic aerosol (SOA) generated from the photooxidation of whole gasoline vapor. Kp values were also measured for ambient n-alkanes sorbing to urban particulate material (UPM) during summer smog episodes in the Los Angeles metropolitan area. Based on the Kp values obtained for the aerosols studied here, for environmental tobacco smoke (ETS), and for a quartz surface, we conclude that G/P partitioning of SOCs to UPM during summer smog episodes is dominated by absorption into the organic fraction in the aerosol. Comparison...

TEST OF A PARAMETERIZATION FOR NOCTURNAL OZONE REDUCTION IN THE RESIDUAL LAYER BY DOWNWARD MIXING DURING SUMMER SMOG SITUATIONS

A simple parameterization describing the ozone depletion in thenocturnal residual layer by a parameter related to the mixing potential ofthe boundary layer was tested over homogeneous terrain in EasternGermany, on the basis of continuous SODAR and near-surface ozonemeasurements. For a summer smog episode in July 1994 the proposedrelationship could not be confirmed. This is attributed to the meteorologicaland transport situation as well as to the site-dependent characteristics.

Budget Calculations for Ozone and Its Precursors: Seasonal and Episodic Features Based on Model Simulations

Results from two air quality models (LOTOS, EURAD) have been used to analyse the contribution of the different terms in the continuity equation to the budget of ozone, NO(x) and PAN. Both models cover large parts of Europe and describe the processes relevant for tropospheric chemistry and dynamics. One of the models is designed to simulate episodes in the order of 1-2 weeks (EURAD), the other is focussing on the seasonal scale (LOTOS). Based on EURAD simulations it is found that the atmospheric boundary layer (ABL) in Central Europe during a summer-smog episode in 1990 acts as a source of ozone, which is partly exported from the production region in Central Europe. About 40% of the ozone produced chemically in the ABL is lost from Central Europe due to net transport (large-scale and turbulent), 40% are deposited within the domain. Vertical mass exchange of ozone is dominated by the prevailing subsidence and averaged vertical mass fluxes are directed downward. Averaged mass fluxes of PAN, which has no stratospheric source, are upward in the upper part of the ABL. The results from LOTOS are discussed for the same episode and for a two month period (July/August 1990). The budget calculation show larger chemical production for the LOTOS model compared to EURAD. The relative importance of deposition and net transport, however, is in the same order. Differences between the two-month calculation and the one week episode are only important for Western Europe where the chemical production is enhanced by 30% during the summer-smog episode. The dependence of the results on initial and boundary values is discussed for ozone on the basis of a simple sensitivity study with EURAD where ozone in the FT is set to 10 ppb initially. This leads to a reversal in the direction of averaged ozone mass fluxes in the upper part of the ABL.

The ozone patterns in the aerological basin of Milan (Italy)

In the last years, photochemical pollution has been recognised as a critical environmental problem. Summer smog episodes occur over large parts of Europe and also in the North of Italy high ozone concentrations are measured. A working group is investigating the ozone distribution and estimating the contribution of breeze circulations transport to the actual ozone levels measured in the territories of the provinces of Milan, Bergamo, Varese and Como in Northern Italy. In this paper the principal results of this outstanding study are presented. Times series of ozone concentrations measured in the last years by the four provincial air pollution networks, including 18 monitoring sites, have been analysed by comparing trends and frequency of exceedances of air quality standard limits. Moreover, a statistical analysis has been made to evaluate similarity among measured ozone concentrations in terms of levels and temporal variability (frequency and peaks distribution, daily shape etc.). This study covers the summer period from June to September 1992 and uses the measured 1-h ozone concentrations in two different test cases. The first case considers day-time ozone data (9:00–20:00); the second one also includes night-time ozone data (0:00–24:00). The method developed is based on hierarchical Cluster Analyses techniques. Every group has been well characterized by an averaged hourly concentration and relative variance. The statistical analyses has shown a summer time gradient of surface ozone concentrations going from south to north of the area under study and interesting similarities among monitoring sites in the day-time maximum peak occurrence.

Influence of topography and biogenic volatile organic compounds emission in the state of Baden‐Württemberg on ozone concentrations during episodes of high air temperatures

A nonhydrostatic mesoscale model which is coupled with a transport and diffusion model and the gas phase mechanism RADM2 is used to study the influence of biogenic volatile organic compounds (VOC) emission on the ozone concentration during episodes of high air temperatures in the state of Baden‐Württemberg, Germany. All model parts, including the determination of the biogenic VOC emissions, are run in a coupled mode. The results of the model simulations are compared with observations for a summer smog episode which occurred in August 1990. Simulations which are carried out without biogenic VOC emissions show a maximum difference in the ozone concentration of 18 ppb, while the maximum ozone values are of the order of 100 ppb. This shows that the biogenic VOC emissions play an important role when high temperatures are present in Baden‐Württemberg. Simulations which are carried out with homogeneous terrain height show differences in the biogenic emissions caused by changes in the temperature distribution. Large differences are also found for the concentration distributions. The differences in the results which are obtained with and without biogenic VOC emissions are decreasing; the maximum difference is about 10 ppb. This demonstrates the necessity of a sufficient treatment of topographic effects in the regional scale.

Acute respiratory effects of low level summer smog in primary school children

We aimed to study the possible effects of exposure to a summer smog episode on the respiratory health of 212 school children. Furthermore, the suitability of the forced oscillation technique (FOT) to demonstrate such effects was evaluated. Acute respiratory symptoms were evaluated by questionnaire and lung function was assessed by spirometry and respiratory impedance measurements. For each child, comparisons were made between measurements performed at baseline (low levels of air pollutant: 55 micrograms.m-3 for SO2 and 58 micrograms.m-3 for NO2 (maximum 24 h means); O3 levels ranged from 2-56 micrograms.m-3 (8 h mean)); and after a summer smog episode (characterized by 8 h O3 levels > 120 micrograms.m-3 (163 micrograms.m-3) and 1 h levels > 160 micrograms.m-3 (215 micrograms.m-3). No significant effects were observed on the prevalence of acute respiratory symptoms. When individual changes in lung function indices (delta LF) were regressed on changes in previous day ozone (8 h mean) and changes in mean daily temperature (delta MTemp), using multiple linear regression analysis, a significant negative association was observed with peak expiratory flow (PEF), but not with other spirometry indices. Although significant associations were observed with reactance at 8 Hz (Xrs8), resonant frequency (f0) and frequency dependence of resistance (FD), the signs of the beta s were opposite to the direction expected when O3 adversely affected the impedance outcomes. In conclusion, in this study short-term exposure to moderately high levels of ozone did not result in clear adverse effects on the respiratory health of the children.(ABSTRACT TRUNCATED AT 250 WORDS)

Ozone and hydrogen peroxide during summer smog episodes over the Swiss Plateau: Measurements and model simulations

As part of the POLLUMET (Pollution and Meteorology in Switzerland) study, measurements of O3, NO2, and H2O2 were made at ground stations, by aircraft, and manned hydrogen balloons to characterize the photochemical processes prevailing during times of high ozone production. During summer smog episodes, elevated ozone concentrations were found over the whole area of the Swiss Plateau, which is a densely populated and industrialized region. However, NO2 concentrations were generally at a low level in the afternoon. An increase of hydrogen peroxide concentration in the mixing layer during photochemical episodes was observed. To understand better the photochemical processes which control ozone formation over the Swiss Plateau, calculations with the Harvard photochemical model and the Harwell photochemical trajectory model were conducted. A comparison of model results with measurements of the triad O3, NO2, and H2O2 indicates an ozone formation under low NOx conditions.

A parameterization of the nocturnal ozone reduction in the residual layer by verticla downward mixing during summer smog situations using sodar data

The reduction of ozone in the nocturnal residual layer by vertical mixing to the surface was investigated for several summer smog episodes on the Swiss plateau in the years 1990 and 1991. Using a limited data set of SODAR measurements and surface ozone concentrations, a parameterization of the ozone depletion in the nocturnal residual layer due to vertical mixing to the ground is proposed. This model is not intended to be physically complete but is rather simple with limited input information required. The nocturnal ozone reduction within the whole planetary boundary layer (nocturnal boundary layer plus residual layer) over the complex terrain of the Swiss plateau for the days investigated is between 20 and 50%.

Acute respiratory effects of summer smog in primary school children

In 535 primary school children we studied the effects of exposure to summer smog on respiratory health. Baseline measurements were performed during low air pollution levels (max. 24-h concentrations of SO 2, O 3 and NO 2 were 55, 49 and 58 mg/m 3, respectively) consisting of lung function measurements using spirometry and the forced oscillation technique (FOT) and the prevalence of respiratory symptoms, determined by a written questionnaire. During a summer smog episode, 212 randomly chosen children were re-examined, characterised by 8-h ozone levels > 120 mg/m 3 (max. 163 mg/m 3) and 1-h ozone levels > 160 mg/m 3 (max. 215 mg/m 3). Overall, small decrements were observed in the forced expiratory volume in 1 s (FEV 1), ( P < 0.05) and the forced expiratory volume between 25 and 75% of the vital capacity ( FEF 25–75% ( P < 0.01). On the contrary, there was a statistically significant decrease in resistance parameters. No increases were observed in the prevalence of acute respiratory symptoms. In conclusion, in this study we found small inconsistent changes in lung function and no increase of respiratory symptoms after short-time exposure to moderately high ozone levels.

Formic acid and acetic acid measurements during the Southern California Air Quality Study

As part of the Southern California Air Quality Study (SCAQS), ambient levels of gas phase formic acid and acetic acid have been measured at four locations: a ‘control’ site (San Nicholas Island), a source-dominated coastal site (Long Beach) and two inland smog receptor sites (Claremont and Palm Springs). Samples were collected on alkaline traps and were analyzed by size exclusion liquid chromatography with ultraviolet detection. Levels of gas phase formic acid (up to 19 ppb) and acetic acid (up to 17 ppb) exhibited diurnal (frequent night-time maxima), spatial and seasonal variations. During summer smog episodes, concentrations increased from 0.6 ppb at the ‘control’ site to up to 13–19 ppb at the inland smog receptor sites reflecting primary emissions and in situ formation during transport inland. The acetic acid/formic acid (A/F) ratio decreased from coastal to inland sites. At the coastal site levels of both acids and the A/F ratio were substantially higher during the fall than during the summer.