Guido Pirovano

Sensitivity of CTM simulations to meteorological input

The objective of this work is to investigate the sensitivity of an Eulerian Chemical Tranport Model to the reconstruction of the wind field. In the framework of City-Delta exercise, three 14-day simulations have been performed, using the same model (CAMx) and different meteorological inputs; these were built combining large-scale analysis, local observations and the output of a high resolution meteorological model (Aladin). When Aladin output is used, stronger surface winds lead to enhanced nighttime mixing, resulting in higher ozone and lower PM10 concentrations in urban areas; on the other hand, the stronger advection associated with Aladin wind seems to help the model reproduce high ozone concentrations during day. The use of local wind observations appears beneficial to model performance.

Evaluation and error apportionment of an ensemble of atmospheric chemistry transport modeling systems : Multivariable temporal and spatial breakdown

Through the comparison of several regional-scale chemistry transport modeling systems that simulate meteorology and air quality over the European and North American continents, this study aims at (i) apportioning error to the responsible processes using timescale analysis, (ii) helping to detect causes of model error, and (iii) identifying the processes and temporal scales most urgently requiring dedicated investigations. The analysis is conducted within the framework of the third phase of the Air Quality Model Evaluation International Initiative (AQMEII) and tackles model performance gauging through measurement-to-model comparison, error decomposition, and time series analysis of the models biases for several fields (ozone, CO, SO2, NO, NO2, PM10, PM2.5, wind speed, and temperature). The operational metrics (magnitude of the error, sign of the bias, associativity) provide an overallsense of model strengths and deficiencies, while apportioning the error to its constituent parts (bias, variance, and covariance) can help assess the nature and quality of the error. Each of the error components is analyzed independently and apportioned to specific processes based on the corresponding timescale (long scale, synoptic, diurnal, and intraday) using the error apportionment technique devised in the former phases of AQMEII. The application of the error apportionment method to the AQMEII Phase 3 simulations provides several key insights. In addition to reaffirming the strong impact of model inputs (emission and boundary conditions) and poor representation of the stable boundary layer on model bias, results also highlighted the high interdependencies among meteorological and chemical variables, as well as among their errors. This indicates that the evaluation of air quality model performance for individual pollutants needs to be supported by complementary analysis of meteorological fields and chemical precursors to provide results that are more insightful from a model development perspective. This will require evaluaion methods that are able to frame the impact on error of processes, conditions, and fluxes at the surface. For example, error due to emission and boundary conditions is dominant for primary species (CO, particulate matter (PM)), while errors due to meteorology and chemistry are most relevant to secondary species, such as ozone. Some further aspects emerged whose interpretation requires additional consideration, such as the uniformity of the synoptic error being region- and model-independent, observed for several pollutants; the source of unexplained variance for the diurnal component; and the type of error caused by deposition and at which scale.

Evaluating Seasonal Model Simulations of Ozone in Northern Italy

High concentrations of tropospheric ozone are quite usual in Mediterranean areas during summer seasons and cause adverse effects on human health and natural ecosystems. In order to capture ozone climatological behaviour and select effective reduction strategies, long-term simulations can be performed. Several authors (Hogrefe et al., 2001; Schmidt et al., 2001; Kasibihatla et al., 2000) present seasonal simulations on regional scale performed by photochemical systems. Usually models are run with a spatial resolution ranging from 36 km to 0.5° over domains extending up to 2–3000 km in each direction. In this paper an urban scale long-term simulation is evaluated. The simulation domain is located in Northern Italy, including Milan metropolitan area. It is characterised by complex terrain, high urban and industrial emissions and a close road network. Due to the presence of the Alps, winds are often weak and circulation shows very heterogeneous patterns. Besides, during anticyclonic stable conditions breeze can develop causing daily circulation of polluted air masses between urban and rural areas. The critical anthropogenic emissions, the frequent stagnating meteorological conditions and the solar radiation regularly cause high ozone level episodes. Due to the described meteorological features, pollutants can give raise to a complex spatial distribution, that is difficult to describe by means of mathematical models even using a detailed spatial resolution. Moreover, in several cases, spatial variability can induce a representativeness reduction of measurement stations, making critical the comparison with model results.

Assessment and economic valuation of air pollution impacts on human health over Europe and the United States as calculated by a multi-model ensemble in the framework of AQMEII3

The impact of air pollution on human health and the associated external costs in Europe and the United States (US) for the year 2010 are modeled by a multi-model ensemble of regional models in the frame of the third phase of the Air Quality Modelling Evaluation International Initiative (AQMEII3). The modeled surface concentrations of O3, CO, SO2 and PM2.5 are used as input to the Economic Valuation of Air Pollution (EVA) system to calculate the resulting health impacts and the associated external costs from each individual model. Along with a base case simulation, additional runs were performed introducing 20 % anthropogenic emission reductions both globally and regionally in Europe, North America and east Asia, as defined by the second phase of the Task Force on Hemispheric Transport of Air Pollution (TF-HTAP2). Health impacts estimated by using concentration inputs from different chemistry–transport models (CTMs) to the EVA system can vary up to a factor of 3 in Europe (12 models) and the United States (3 models). In Europe, the multi-model mean total number of premature deaths (acute and chronic) is calculated to be 414 000, while in the US, it is estimated to be 160 000, in agreement with previous global and regional studies. The economic valuation of these health impacts is calculated to be EUR 300 billion and 145 billion in Europe and the US, respectively. A subset of models that produce the smallest error compared to the surface observations at each time step against an all-model mean ensemble results in increase of health impacts by up to 30 % in Europe, while in the US, the optimal ensemble mean led to a decrease in the calculated health impacts by ~ 11 %. A total of 54 000 and 27 500 premature deaths can be avoided by a 20 % reduction of global anthropogenic emissions in Europe and the US, respectively. A 20 % reduction of North American anthropogenic emissions avoids a total of ~ 1000 premature deaths in Europe and 25 000 total premature deaths in the US. A 20 % decrease of anthropogenic emissions within the European source region avoids a total of 47 000 premature deaths in Europe. Reducing the east Asian anthropogenic emissions by 20 % avoids ~ 2000 total premature deaths in the US. These results show that the domestic anthropogenic emissions make the largest impacts on premature deaths on a continental scale, while foreign sources make a minor contribution to adverse impacts of air pollution.

WRF evaluation exercise using open sea in situ measurements

This work regards a model evaluation exercise concerning the WRF meteorological model and in situ measurements collected both over land, at four WMO meteorological stations, and over open sea, by ODAS Italia 1, the only spar buoy in the Mediterranean Sea. In particular, this exercise is finalised to understand the ability of the model to act as meteorological pre-processor to simulate aerosol emissions from the sea, an important factor to correctly predict pollutant levels. The test is carried out for the August to December 2005 period over the Ligurian Sea region, a very complex area where the strong air-sea interactions and orography significantly affect the atmospheric circulation. Performances of two model versions, WRF-ARW 3.0 and WRF-ARW 3.2.1, applied at two different horizontal resolutions, have been compared. The results show that the new parameterisations introduced in WRF 3.2.1 improve the performance of the model with respect to version 3.2.0. Increasing the model domain resolution from 15 km to 5 km does not generally improve the model performance, except for the wind direction reconstruction. The model proved its reliability as meteorological processor, although further efforts are required to improve wind field simulation, mainly in order to reduce the low bias still affecting the reconstruction at high wind speed.

Annual simulation of secondary pollution over northern Italy

A secondary pollution modelling system for simulating airborne dispersion and chemical reactions is applied over a regional scale domain located in the North-West of Italy, where urban and industrial areas are present. It was found an overestimation of NO2 in the urban areas, probably due to an underestimation of the vertical diffusivity; the analysis of OX confirms that the discrepancies in O3 and NO2 are mainly due to local scale effects; the model shows a general underestimation of the observed PM10 concentrations due to the uncertainties in the emission inventories, spatial resolution, and the adopted aerosol modelling approach.

Application of Advanced Particulate Matter Source Apportionment Techniques in the Northern Italy Basin

This work describes the results of the CAMx modelling system application aimed at reconstructing the particulate matter concentration over the Northern Italy basin and analysing the role played by the main emission sources on the pollution levels. Simulations have been performed on yearly basis in the frame of two different modelling exercises. The present analysis has been performed taking into account an overlapping period, covering February 2004. As a first step, CAMx results have been compared to a considerable data set of observed concentrations of NO2 and PM10. Model has been able to correctly reproduce the daily evolution and spatial variability of NO2, while some underestimations of PM10 concentrations have been highlighted. Then the Particulate Source Apportionment tool (PSAT) has been applied, in order to discriminate the contribution of several key emission sectors such as transport, domestic heating and power plants, in relation to three emission areas. Road transport appears to be the most responsible sector of PM10 concentration, especially in the area between Milan and Turin. The urban area of Milan is characterised by high PM10 concentration with an important contribution by road transport and domestic heating. The analysis has also pointed out the increasing relevance of the emissions coming from areas outside the city during critical pollution episodes, when severe stagnant conditions emphasise the role of secondary particulate matter. Finally, the comparison between the two PSAT applications has put in evidence, as a whole, quite coherent distributions of the relative contribution to PM10 concentration, thus proving the robustness of the source apportionment results. The main differences concerned domestic heating contribution, clearly related to the discrepancies in the emission inventories.

Lagrangian micromixing modelling of reactive scalar statistics: scalar mixing layer in decaying grid turbulence

A Lagrangian micro-mixing numerical model estimates the concentration statistics of reactive pollutants (NO, O3 and NO2) of a scalar mixing layer in decaying grid turbulence. A stochastic macro-mixing scheme computes the fluid particle trajectories, which describe the turbulent flow (Lagrangian turbulence), whereas the micro-mixing scheme interaction by the exchange with the conditional mean (IECM), implementing a new formulation for the mixing time, represents the dissipation of concentration turbulent fluctuations due to molecular diffusion. The non-homogeneous reaction-dominated limit (NHRDL) of the conserved scalar theory simulates chemical reactions. The numerical model integrates these three schemes and is validated by comparison with experimental and direct numerical simulation (DNS) data, whereas inter-comparisons with other numerical models are also reported. The study focuses on the reliability of Lagrangian stochastic models in representing micro-scale pollutant dispersion (air quality) and the importance of representing chemical reactions depending on instantaneous concentrations rather than their means.

Source apportionment technique: inorganic aerosol transformation processes in the Milan area

The CAMx chemical and transport Eulerian model has been applied over a domain focused on the Milan area (Northern Italy) for the whole 2004, on the basis of CityDelta III project input data set. Model results have been analysed by mean of the Source Apportionment technique at the Milan receptor. A quantitative analysis of the main processes governing the Secondary Inorganic Aerosols (SIAs) production showed that the overall efficiency of the transformation processes is influenced by several factors, which prevents defining simple relationships between emissions and secondary aerosol compounds.

Chapter 4.2 Application and sensitivity analysis of CAMx and CHIMERE air quality models in a coastal area

Abstract This work is dedicated to the evaluation of the influence of input data on the ability of chemical transport models to reconstruct a given pollution episode. Such a question remains critical in the frame of air pollution forecasting and management. The study relies on the large European ESCOMPTE campaign that took place in the Marseilles area (South-East of France) in summer 2001, and that was dedicated to the constitution of a detailed 3D chemical and meteorological database for a CTM intercomparison exercise. The huge amount of measurement data indeed allowed us to investigate the behaviour of CTMs in a complex environment. In fact, the domain is characterised by the presence of large urban and industrial poles along the coastline served by a dense road network. Submitted to land-sea breeze phenomena, it shows an increasing orographic altimetry which constrains the transport of polluted plumes inland. Simulations, carried out with CAMx and CHIMERE, were focused on two intense ozone episodes: 21–23 June 2001 (moderate synoptic wind) and 24–26 June 2001 (local sea–land breeze circulation). The specificity of this work is to compare the models outputs both in their original configurations and gradually changing the input configuration (meteorological data, boundary conditions) in order to quantify the related effect on the results. The model results were compared with the very rich set of dynamical parameters and chemical data of the campaign, obtained from ground stations, Lidar, aircrafts, boats, balloons, radiosoundings. Statistical indices and performance indicators were also set up and showed that the models could correctly reproduce photochemical smog phenomena over the Marseille area.