Long-term trend in surface ozone in Houston-Galveston-Brazoria: Sectoral contributions based on changes in volatile organic compounds

This study investigated the long-term variations in ambient levels of surface ozone, volatile organic compounds (VOCs), and nitrogen oxides (NO_x) within the Houston-Galveston-Brazoria (HGB) region. Analysis of ozone levels revealed an overall reduction in the maximum daily 8-h average ozone (MDA8 O₃) from 2000 to 2019 (April-October) with an average rate of ∼ -0.48 ppb/yr across HGB. With a few exceptions, the MDA8 O₃ reduction rates were more pronounced for the monitoring sites closer to the Houston Ship Channel (HSC). Meanwhile, ambient levels of NO_x and most VOC species (across the three representative sites as Houston Bayland Park, Haden Road, and Lynchburg Ferry) decreased significantly within the same investigation period, reflecting the impact of emission reductions. The positive matrix factorization (PMF) model applied to the mentioned sites identified regional background ozone, petrochemical emissions, engine combustion, natural gas/fuel evaporation, and solvent/painting/rubber industries as the major sources of MDA8 O₃. The regional background ozone was the predominant source, accounting for 59-70% of MDA8 O₃ across the three sites. Regarding the local anthropogenic emissions, natural gas/fuel evaporation was the largest contributor (19.5 ± 6.1%) to MDA8 O₃ at Houston Bayland Park, whereas petrochemical facilities (10.9 ± 4.9%) and solvent/painting/rubber industries (18.1 ± 9.5%) were the largest factor at Haden Road and Lynchburg Ferry, respectively. Notable reductions were found in the contributions of petrochemical emissions, engine combustion, and natural gas/fuel evaporation to MDA8 O₃ within 2000-2019, but an increasing trend was revealed in the role of solvent/painting/rubber industries on MDA8 O₃ most probably due to the enhanced demand for their products. Results of this study corroborated the success of emission control policies in limiting ozone precursors and provided useful details for prioritizing emission reduction policies to further reduce ozone pollution in the HGB.

What Are the Sectors Contributing to the Exceedance of European Air Quality Standards over the Iberian Peninsula? A Source Contribution Analysis

The Iberian Peninsula, located in southwestern Europe, is exposed to frequent exceedances of different threshold and limit values of air pollution, mainly related to particulate matter, ozone, and nitrous oxide. Source apportionment modeling represents a useful modeling tool for evaluating the contribution of different emission sources or sectors and for designing useful mitigation strategies. In this sense, this work assesses the impact of various emission sectors on air pollution levels over the Iberian Peninsula using a source contribution analysis (zero-out method). The methodology includes the use of the regional WRF + CHIMERE modeling system (coupled to EMEP emissions). In order to represent the sensitivity of the chemistry and transport of gas-phase pollutants and aerosols, several emission sectors have been zeroed-out to quantify the influence of different sources in the area, such as on-road traffic or other mobile sources, combustion in energy generation, industrial emissions or agriculture, among others. The sensitivity analysis indicates that large reductions of precursor emissions (coming mainly from energy generation, road traffic, and maritime-harbor emissions) are needed for improving air quality and attaining the thresholds set in the European Directive 2008/50/EC over the Iberian Peninsula.

Comprehensive Insights Into O3 Changes During the COVID-19 From O3 Formation Regime and Atmospheric Oxidation Capacity

Economic activities and the associated emissions have significantly declined during the 2019 novel coronavirus (COVID-19) pandemic, which has created a natural experiment to assess the impact of the emitted precursor control policy on ozone (O3) pollution. In this study, we utilized comprehensive satellite, ground-level observations, and source-oriented chemical transport modeling to investigate the O3 variations during the COVID-19 pandemic in China. Here, we found that the significant elevated O3 in the North China Plain (40%) and Yangtze River Delta (35%) were mainly attributed to the enhanced atmospheric oxidation capacity (AOC) in these regions, associated with the meteorology and emission reduction during lockdown. Besides, O3 formation regimes shifted from VOC-limited regimes to NOx-limited and transition regimes with the decline of NOx during lockdown. We suggest that future O3 control policies should comprehensively consider the effects of AOC on the O3 elevation and coordinated regulations of the O3 precursor emissions.

Identification of close relationship between atmospheric oxidation and ozone formation regimes in a photochemically active region

Understanding ozone (O3) formation regime is a prerequisite in formulating an effective O3 pollution control strategy. Photochemical indicator is a simple and direct method in identifying O3 formation regimes. Most used indicators are derived from observations, whereas the role of atmospheric oxidation is not in consideration, which is the core driver of O3 formation. Thus, it may impact accuracy in signaling O3 formation regimes. In this study, an advanced three-dimensional numerical modeling system was used to investigate the relationship between atmospheric oxidation and O3 formation regimes during a long-lasting O3 exceedance event in September 2017 over the Pearl River Delta (PRD) of China. We discovered a clear relationship between atmospheric oxidative capacity and O3 formation regime. Over eastern PRD, O3 formation was mainly in a NOx-limited regime when HO2/OH ratio was higher than 11, while in a VOC-limited regime when the ratio was lower than 9.5. Over central and western PRD, an HO2/OH ratio higher than 5 and lower than 2 was indicative of NOx-limited and VOC-limited regime, respectively. Physical contribution, including horizontal transport and vertical transport, may pose uncertainties on the indication of O3 formation regime by HO2/OH ratio. In comparison with other commonly used photochemical indicators, HO2/OH ratio had the best performance in differentiating O3 formation regimes. This study highlighted the necessities in using an atmospheric oxidative capacity-based indicator to infer O3 formation regime, and underscored the importance of characterizing behaviors of radicals to gain insight in atmospheric processes leading to O3 pollution over a photochemically active region.

The Impact of the COVID-19 Pandemic on Ambient Air Quality in China: A Quasi-Difference-in-Difference Approach

The novel coronavirus (COVID-19) pandemic has provided a distinct opportunity to explore the mechanisms by which human activities affect air quality and pollution emissions. We conduct a quasi-difference-in-differences (DID) analysis of the impacts of lockdown measures on air pollution during the first wave of the COVID-19 pandemic in China. Our study covers 367 cities from the beginning of the lockdown on 23 January 2020 until April 22, two weeks after the lockdown in the epicenter was lifted. Static and dynamic analysis of the average treatment effects on the treated is conducted for the air quality index (AQI) and six criteria pollutants. The results indicate that, first, on average, the AQI decreased by about 7%. However, it was still over the threshold set by the World Health Organization. Second, we detect heterogeneous changes in the level of different pollutants, which suggests heterogeneous impacts of the lockdown on human activities: carbon monoxide (CO) had the biggest drop, about 30%, and nitrogen dioxide (NO₂) had the second-biggest drop, 20%. In contrast, ozone (O₃) increased by 3.74% due to the changes in the NO_x/VOCs caused by the decrease in NO_x, the decrease of O₃ titration, and particulate matter concentration. Third, air pollution levels rebounded immediately after the number of infections dropped, which indicates a swift recovery of human activities. This study provides insights into the implementation of environmental policies in China and other developing countries.

Modeling Ozone Source Apportionment and Performing Sensitivity Analysis in Summer on the North China Plain

In recent years, air quality issues due to fine particulate matter have been sufficiently treated. However, ozone (O3) has now become the primary pollutant in summer on the North China Plain (NCP). In this study, a three-dimensional chemical transport model (the Nested Air Quality Prediction Model System, NAQPMS) coupled with an online source apportionment module was applied to investigate the sources of O3 pollution over the NCP. Generally, the NAQPMS adequately captured the observed spatiotemporal features of O3 during the period of July 1st to August 31st in 2017 on the NCP. The results of the source apportionment indicated that the contributions of local emissions and transport from the NCP accounted for the largest proportion of O3, with magnitudes of 25% and 39%, respectively. Compared with those in the average monthly results, the local contribution and regional transport during O3 episodes on the NCP increased by 7% and 10%, respectively. Based on sensitivity tests, two thresholds of the sensitivity indicator P(H2O2)/P(HNO3) were detected, at 0.08 and 0.2. Ozone formation in the urban sites of Beijing, Tianjin, and the southern part of Hebei Province was controlled by VOCs, while the other sites were mainly controlled by NOX. Biogenic emissions contributed approximately 18% to O3 formation in July in the southwestern part of Hebei Province.

Air quality, health impacts and burden of disease due to air pollution (PM10, PM2.5, NO2 and O3): Application of AirQ+ model to the Camp de Tarragona County (Catalonia, Spain)

The purpose of this study was to assess the impact to human health of air pollutants, through the integration of different technics: data statistics (spatial and temporal trends), population attributable fraction using AIRQ+ model developed by the WHO, and burden of disease using Disability-Adjusted Life Years (DALYs). The levels of SO₂, NO, NO₂, O₃, H₂S, benzene, PM₁₀, PM_2.5, CO, benzo(a)pyrene and metals, obtained between 2005 and 2017 from the air quality monitoring network across Camp de Tarragona County, were temporally and spatially determined. Health impacts were evaluated using the AIRQ+ model. Finally, the burden of disease was assessed through the calculation of Years of Lost life (YLL) and Years Lost due to Disability (YLD). In general terms, air quality was good according to European quality standards, but it did not fulfil the WHO guidelines, especially for O₃, PM₁₀ and PM_2.5. Several decreasing (NO, NO₂, SO₂, PM₁₀ and benzene) and an increasing (O₃) temporal trend were found. Correlation between unemployment rate and air pollutant levels was found, pointing that the economic crisis (2008-2014) was a factor influencing the air pollutant levels. Reduction of air pollutant levels (PM_2.5) to WHO guidelines in the Camp de Tarragona County would decrease the adult mortality between 23 and 297 cases per year, which means between 0.5 and 7% of all mortality in the area. In this County, for lung cancer, ischemic heart disease, stroke, and chronic obstructive pulmonary disease due to levels of PM_2.5 above the WHO threshold limits, DAYLs were 240 years. This means around 80 DALYs for 100,000 persons every year -between 2005 and 2017. Population attributable fraction (PAF) and burden of disease (DALYs) methodologies are suitable tools for regional and national policymakers, who must take decisions to prevent and to control air pollution and to analyse the cost-effectiveness of interventions.

Responses of PM2.5 and O3 concentrations to changes of meteorology and emissions in China

Tremendous efforts have been made to reduce the severe air pollution in China since 2013. However, the annual and peak fine particulate matter (PM_2.5) concentrations during severe events in winter did not always reduce as expected. This is partially due to the inter-annual variation of meteorology, which affects the emission, transport, transformation, and deposition processes of air pollutants. In this study, the responses of PM_2.5 and ozone (O₃) concentrations to changes in emission and meteorology from 2013 to 2015 were investigated based on ambient measurements and the Community Multi-Scale Air Quality (CMAQ) model simulations with anthropogenic emissions. It is found that emission reductions in 2014 and 2015 effectively reduced PM_2.5 concentrations by 23.9 and 43.5 μg/m³, respectively, but was partially counteracted by unfavorable meteorology. The negative effects from unfavorable meteorology were significant in extreme pollution events. For example, in December 2015, unfavorable meteorology caused a great increase (90 μg/m³) of PM_2.5 in Beijing. Reduction of primary PM and gaseous precursors led to 13.4 and 16.5 ppb increase of O₃-8 h daily concentrations in the summertime in 2014 and 2015 in comparison of 2013, which was likely caused by the increase of solar actinic flux due to PM reduction. In addition, reduction of nitrogen oxides (NOx) emissions in areas with negative NOx-O₃ sensitivity could lead to an increase of O₃ formation when the reduction of volatile organic compounds (VOCs) was not sufficient. This unintended enhanced O₃ formation could also lead to higher O₃ in downwind areas. This study emphasizes the role of meteorology in pollution control, validates the effectiveness of PM_2.5 control measures in China, and highlights the importance of appropriate joint reduction of NOx and VOCs to simultaneously decrease O₃ and PM_2.5 for higher air quality.

Development and application of observable response indicators for design of an effective ozone and fine particle pollution control strategy in China

Designing effective control policies requires efficient quantification of the nonlinear response of air pollution to emissions. However, neither the current observable indicators nor the current indicators based on response-surface modeling (RSM) can fulfill this requirement. Therefore, this study developed new observable RSM-based indicators and applied them to ambient fine particle (PM_2.5) and ozone (O₃) pollution control in China. The performance of these observable indicators in predicting O₃ and PM_2.5 chemistry was compared with that of the current RSM-based indicators. H₂O₂×HCHO/NO₂ and total ammonia ratio, which exhibited the best performance among indicators, were proposed as new observable O₃- and PM_2.5-chemistry indicators, respectively. Strong correlations between RSM-based and traditional observable indicators suggested that a combination of ambient concentrations of certain chemical species can serve as an indicator to approximately quantify the response of O₃ and PM_2.5 to changes in precursor emissions. The observable RSM-based indicator for O₃ (observable peak ratio) effectively captured the strong NO_x-saturated regime in January and the NO_x-limited regime in July, as well as the strong NO_x-saturated regime in northern and eastern China and their key regions, including the Yangtze River Delta and Pearl River Delta. The observable RSM-based indicator for PM_2.5 (observable flex ratio) also captured strong NH₃-poor condition in January and NH₃-rich condition in April and July, as well as NH₃-rich in northern and eastern China and the Sichuan Basin. Moreover, analysis of these newly developed observable response indicators suggested that the simultaneous control of NH₃ and NO_x emissions produces greater benefits in provinces with higher PM_2.5 exposure by up to 1.2 μg m^-3 PM_2.5 per 10 % NH₃ reduction compared with NO_x control only. Control of volatile organic compound (VOC) emissions by as much as 40 % of NO_x controls is necessary to obtain the cobenefits of reducing both O₃ and PM_2.5 exposure at the national level when controlling NO_x emissions. However, the VOC-to-NO_x ratio required to maintain benefits varies significantly from 0 to 1.2 in different provinces, suggesting that a more localized control strategy should be designed for each province.

Factors dominating 3-dimensional ozone distribution during high tropospheric ozone period

Data from an in situ monitoring network and five ozone sondes are analysed during August of 2012, and a high tropospheric ozone episode is observed around the 8th of AUG. The Community Multi-scale Air Quality (CMAQ) model and its process analysis tool were used to study factors and mechanisms for high ozone mixing ratio at different levels of ozone vertical profiles. A sensitive scenario without chemical initial and boundary conditions (ICBCs) from MOZART4-GEOS5 was applied to study the impact of stratosphere-troposphere exchange (STE) on vertical ozone. The simulation results indicated that the first high ozone peak near the tropopause was dominated by STE. Results from process analysis showed that: in the urban area, the second peak at approximately 2 km above ground height was mainly caused by local photochemical production. The third peak (near surface) was mainly caused by the upwind transportation from the suburban/rural areas; in the suburban/rural areas, local photochemical production of ozone dominated the high ozone mixing ratio from the surface to approximately 3 km height. Furthermore, the capability of indicators to distinguish O₃-precursor sensitivity along the vertical O₃ profiles was investigated. Two sensitive scenarios, which had cut 30% anthropogenic NO_X or VOC emissions, showed that O₃-precursor indicators, specifically the ratios of O₃/NOy, H₂O₂/HNO₃ or H₂O₂/NO_Z, could partly distinguish the O₃-precursor sensitivity between VOCs-sensitive and NOx-sensitive along the vertical profiles. In urban area, the O₃-precursor relationship transferred from VOCs-sensitive within the boundary layer to NOx-sensitive at approximately 1-3 km above ground height, further confirming the dominant roles of transportation and photochemical production in high O₃ peaks at the near-ground layer and 2 km above ground height, respectively.

The use of experimental data and their uncertainty for assessing ozone photochemistry in the Eastern Iberian Peninsula

Observation-based methods are useful tools to explore the sensitivity of ozone concentrations to precursor controls. With the aim of assessing the ozone precursor sensitivity in two locations: Paterna (suburban) and Villar del Arzobispo (rural) of the Turia river basin in the east of Spain, the photochemical indicator O(3)/NO(y) and the Extent-of-Reaction (EOR) parameter have been calculated from field measurements. In Paterna, the O(3)/NO(y) ratio varied from 0 to 13 with an average value of 5.1 (SD 3.2), whereas the averaged value for the EOR was 0.43 (SD 0.14). In Villar del Arzobispo, the O(3)/NO(y) ratio changed from 5 to 30 with a mean value of 13.6 (SD 4.7) and the EOR gave an averaged value of 0.72 (SD 0.11). The results show two different patterns of ozone production as a function of the location. The suburban area shows a VOC-sensitive regime whereas the rural one shows a transition regime close to NO(x)-sensitive conditions. No seasonal differences in these regimes are observed along the monitoring campaigns. Finally, an analysis of the influence of the measurement quality of NO(y), NO(x) and O(3) on the uncertainty of the O(3)/NO(y) ratio and the EOR was performed showing that the uncertainty of O(3)/NO(y) is not dependent on either its value or the individual values of O(3) and NO(y) but just on the quality of O(3) and NO(y) measurements. The maximum uncertainty is 26% as long as the combined uncertainties of O(3) and NO(y) remain below the 7.5%. The case of the EOR is different and its uncertainty depends on both the value of the EOR parameter and the individual concentration values of NO(y) and NO(x). The uncertainty of the EOR estimation can be very high (>200%) if the combined uncertainties of both NO(y) and NO(x) are high (>7.5%), or especially, if u(NO(y)) and u(NO(x)) differ considerably from each other (>3.5%).

Assessment of Kalman filter bias-adjustment technique to improve the simulation of ground-level ozone over Spain

The CALIOPE air quality modelling system has been used to diagnose ground level O(3) concentration for the year 2004, over the Iberian Peninsula. We investigate the improvement in the simulation of daily O(3) maximum by the use of a post-processing such as the Kalman filter bias-adjustment technique. The Kalman filter bias-adjustment technique is a recursive algorithm to optimally estimate bias-adjustment terms from previous measurements and model results. The bias-adjustment technique improved the simulation of daily O(3) maximum for the entire year and the all the stations considered over the whole domain. The corrected simulation presents improvements in statistical indicators such as correlation, root mean square error, mean bias, and gross error. After the post-processing the exceedances of O(3) concentration limits, as established by the European Directive 2008/50/CE, are better reproduced and the uncertainty of the modelling system, as established by the European Directive 2008/50/CE, is reduced from 20% to 7.5%. Such uncertainty in the model results is under the established EU limit of the 50%. Significant improvements in the O(3) timing and amplitude of the daily cycle are also observed after the post-processing. The systematic improvements in the O(3) maximum simulations suggest that the Kalman filter post-processing method is a suitable technique to reproduce accurate estimate of ground-level O(3) concentration. With this study we evince that the adjusted O(3) concentrations obtained after the post-process of the results from the CALIOPE system are a reliable means for real near time O(3) forecasts.

An annual assessment of air quality with the CALIOPE modeling system over Spain

The CALIOPE project, funded by the Spanish Ministry of the Environment, aims at establishing an air quality forecasting system for Spain. With this goal, CALIOPE modeling system was developed and applied with high resolution (4km×4km, 1h) using the HERMES emission model (including emissions of resuspended particles from paved roads) specifically built up for Spain. The present study provides an evaluation and the assessment of the modeling system, coupling WRF-ARW/HERMES/CMAQ/BSC-DREAM8b for a full-year simulation in 2004 over Spain. The evaluation focuses on the capability of the model to reproduce the temporal and spatial distribution of gas phase species (NO(2), O(3), and SO(2)) and particulate matter (PM10) against ground-based measurements from the Spanish air quality monitoring network. The evaluation of the modeling results on an hourly basis shows a strong dependency of the performance of the model on the type of environment (urban, suburban and rural) and the dominant emission sources (traffic, industrial, and background). The O(3) chemistry is best represented in summer, when mean hourly variability and high peaks are generally well reproduced. The mean normalized error and bias meet the recommendations proposed by the United States Environmental Protection Agency (US-EPA) and the European regulations. Modeled O(3) shows higher performance for urban than for rural stations, especially at traffic stations in large cities, since stations influenced by traffic emissions (i.e., high-NO(x) environments) are better characterized with a more pronounced daily variability. NO(x)/O(3) chemistry is better represented under non-limited-NO(2) regimes. SO(2) is mainly produced from isolated point sources (power generation and transformation industries) which generate large plumes of high SO(2) concentration affecting the air quality on a local to national scale where the meteorological pattern is crucial. The contribution of mineral dust from the Sahara desert through the BSC-DREAM8b model helps to satisfactorily reproduce episodic high PM10 concentration peaks at background stations. The model assessment indicates that one of the main air quality-related problems in Spain is the high level of O(3). A quarter of the Iberian Peninsula shows more than 30days exceeding the value 120μgm(-3) for the maximum 8-h O(3) concentration as a consequence of the transport of O(3) precursors downwind to/from the Madrid and Barcelona metropolitan areas, and industrial areas and cities in the Mediterranean coast.

Applying model simulation and photochemical indicators to evaluate ozone sensitivity in southern Taiwan

Ozone sensitivity was investigated using CAMx simulations and photochemical indicator ratios at three sites (Pingtung City, Chao-Chou Town, and Kenting Town) in Pingtung County in southern Taiwan during 2003 and 2004. The CAMx simulations compared fairly well with the hourly concentrations of ozone. Simulation results also showed that Pingtung City was mainly a volatile organic compounds (VOC)-sensitive regime, while Chao-Chou Town was either a VOC-sensitive or a NOx-sensitive regime, depending on the seasons. Measurements of three photochemical indicators (H2O2, HNO3, and NOy) were conducted, and simulated three transition ranges of H2O2/HNO3 (0.5-0.8), O3/HNO3 (10.3-16.2) and O3/NOy (5.7-10.8) were adopted to assess the ozone sensitive regime at the three sites. The results indicated that the three transition ranges yield consistent results with CAMx simulations at most times at Pingtung City. However, both VOC-sensitive and NOx-sensitive regimes were important at the rural site Chao-Chou Town. Kenting Town, a touring site at the southern end of Taiwan, was predominated by a NOx-sensitive regime in four seasons.

Characterization of ozone precursor volatile organic compounds in urban atmospheres and around the petrochemical industry in the Tarragona region

This paper reports the results of an assessment of volatile organic compound (VOCs) levels in ambient air in samples collected at urban and industrial sites in southern Catalonia, which is home to one of the most important petrochemical complexes in southern Europe. This study contains data from a total of 192 samples collected in 2007, from May to October, at six air pollution measurement stations within the area of influence of several chemical and petrochemical industrial plants. The ambient air concentrations of a group of 65 VOCs, some of them ozone precursors, were determined by active sampling into sorbent tubes, thermal desorption and gas chromatography-mass spectrometry. At the same time, several meteorological parameters were also recorded, and levels of NO, NO(2) and O(3) measured by the automatic stations, have been included in the study as well. Ambient air profiles of the different areas were studied, and the ozone formation dependent on VOCs and NO(2) levels was also analysed, taking into account the photochemical ozone creation potential (POCP) for different groups of VOCs.

High resolution modeling of the effects of alternative fuels use on urban air quality: introduction of natural gas vehicles in Barcelona and Madrid Greater Areas (Spain)

The mitigation of the effects of on-road traffic emissions on urban air pollution is currently an environmental challenge. Air quality modeling has become a powerful tool to design environment-related strategies. A wide range of options is being proposed; such as the introduction of natural gas vehicles (NGV), biofuels or hydrogen vehicles. The impacts on air quality of introducing specific NGV fleets in Barcelona and Madrid (Spain) are assessed by means of the WRF-ARW/HERMES/CMAQ modeling system with high spatial-temporal resolution (1 km(2), 1 h). Seven emissions scenarios are defined taking into account the year 2004 vehicle fleet composition of the study areas and groups of vehicles susceptible of change under a realistic perspective. O(3) average concentration rises up to 1.3% in Barcelona and up to 2.5% in Madrid when introducing the emissions scenarios, due to the NO(x) reduction in VOC-controlled areas. Nevertheless, NO(2), PM10 and SO(2) average concentrations decrease, up to 6.1%, 1.5% and 6.6% in Barcelona and up to 20.6%, 8.7% and 14.9% in Madrid, respectively. Concerning SO(2) and PM10 reductions the most effective single scenario is the introduction of 50% of NGV instead of the oldest commercial vehicles; it also reduces NO(2) concentrations in Barcelona, however in Madrid lower levels are attained when substituting 10% of the private cars. This work introduces the WRF-ARW/HERMES/CMAQ modeling system as a useful management tool and proves that the air quality improvement plans must be designed considering the local characteristics.

The use of a modelling system as a tool for air quality management: annual high-resolution simulations and evaluation

The high levels of air pollutants over the North-Western Mediterranean (NWM) exceed the thresholds set in current air quality regulations. They demand a detailed diagnosis of those areas where the exceedances of thresholds related to human health are found. In this sense, there is a need for modelling studies for the specific area of the NWM that take into account the annual cycle to address the diagnosis of air pollution. A new approach to the modelling of air quality in the NWM has been adopted by combining the WRF-EMICAT-CMAQ-DREAM modelling system to diagnose the current status of the levels of photochemical air pollution (focusing on ozone, O(3); nitrogen dioxide, NO(2); carbon monoxide, CO; and particulate matter, PM10) in the area during an annual cycle (year 2004). The complexity of the area of study requires the application of high spatial and temporal resolution (2 km and 1 h). The annual simulations need to cover the complex different meteorological situations and types of episodes of air pollution in the area of study. The outputs of the modelling system are evaluated against observations from 52 meteorological and 59 air quality stations belonging to the Environmental Department of the Catalonia Government (Spain), which involve a dense and accurate spatial distribution of stations in the territory (32,215 km(2)). The results indicate a good behaviour of the model in both coastal and inland areas of the NWM, with a slight trend to the overestimation of tropospheric O(3) concentrations and the underestimation of other photochemical pollutants (NO(2), CO and PM10). The modelling diagnosis indicates that the main air quality-related problems in the NWM are the exceedances of the 1-hr O(3) information threshold set in the Directive 2002/3/EC (180 microg m(-3)) as a consequence of the transport of O(3) precursors downwind the Barcelona Greater Area (BGA); and the exceedances of the annual value for the protection of human health for NO(2) and PM10 (40 microg m(-3), Directive 1999/30/EC), both in the BGA, as a consequence of the high traffic-related emissions.

High temporal resolution measurements of ozone precursors in a rural background station. A two-year study

We present a very complete database of individual non-methane hydrocarbon (NMHC) measurements with high temporal resolution (hourly) in a rural background atmosphere. We show their use to characterize the biogenic NMHC as well as to identify the transport and impact of anthropogenic NMHC on rural areas. In January 2003 an automatic GC-FID analyzer of volatile organic compounds between 2 and 10 carbon atoms (C2-C10 VOCs) was placed in the centre of the Valderejo Natural Park in northern Iberia (42.87 degrees N, 3.22 degrees W), far away from important cities. The system operated continuously until December 2004. Data coverage was higher than 70% for a total of 59 VOC of both anthropogenic and biogenic origin, with detection limits in the range of pptv. Our results allow for the description of the behaviour of these compounds, in order to identify external impacts arriving to the sampling site which has been recognized to be highly representative of a rural background atmosphere. Biogenic VOC concentrations have been compared also with the calculated emissions, using Guenther's algorithm, and the discrepancies interpreted in terms of the different reactivity of such compounds.

Development of the high spatial resolution EMICAT2000 emission model for air pollutants from the north-eastern Iberian Peninsula (Catalonia, Spain)

Ozone (O(3)) pollution episodes take place in Catalonia (NE of the Iberian Peninsula), mainly during summertime. The complex O(3) behaviour could be understood by using a Chemical Transport Model (CTM). Emission inventories provide the spatial and temporal emissions distribution of the O(3) precursors and other pollutants required by this approach. We developed the EMICAT2000 model with high spatial (cells of 1 km(2)) and temporal (1h) resolutions, to estimate the emissions during the year 2000 from Catalonia. Total annual emissions were 107 kt yr(-1) of NO(x), 137 kt yr(-1) of NMVOC, 267 kt yr(-1) of CO, 65 kt yr(-1) of SO(2), 24 kt yr(-1) of TSP and 32,175 kt yr(-1) of equivalent CO(2). Main NO(x) sources are on-road traffic (58%) and industries (38%). Main NMVOC sources are on-road traffic (36%), vegetation (34%) and use of solvents (13%). Speciation was established according to the Carbon Bond IV mechanism. EMICAT2000 generates directly the data files required for the third generation CTM Models-3/CMAQ.