The heterogeneous interaction of trace gases on mineral dust and soot:kinetics and mechanism

The present thesis work deals with the investigation of the heterogeneous reactions involving nitrate radical (NO3), dinitrogen pentoxide (N2O5) and ozone (O3) on surrogates of atmospheric mineral dust particles characteristic of the troposphere. An additional investigation of heterogeneous reaction of NO3 on flame soot was carried out. The goal is to characterize the kinetics (the uptake coefficient γ) as well as the reaction products. The obtained results are intended to provide reliable data for numerical modelling studies. The experiments were performed in a very low pressure flow reactor (Knudsen cell reactor), coupled to mass spectrometry (MS) and optical probing (Resonance Enhanced Multiphoton Ionization (REMPI)). The used mineral dust powder samples were: Kaolinite, CaCO3, natural limestone, Saharan Dust and Arizona Test Dust. Two different types of soot were produced: soot originating from a rich decane flame at a high fuel/oxygen ratio ("grey" soot) and soot generated from a lean flame at a low fuel/oxygen ratio ("black" soot). Uptake experiments of NO3 on mineral dust were carried out under continuous molecular flow conditions (steady state) at 298 ± 2 K using the thermal decomposition of N2O5 as a NO3 source. In situ laser detection (REMPI) was employed in addition to beam-sampling electron-impact mass spectrometry in order to specifically detect NO2 and NO in the presence of N2O5, NO3 and HNO3. We found a steady state uptake coefficient γss ranging from (3.4 ± 1.6) × 10-2 for natural limestone to 0.12 ± 0.08 for Saharan Dust with γss decreasing as [NO3] increased. NO3 adsorbed on mineral dust led to uptake of NO2 in an Eley-Rideal mechanism where usually no uptake is observed in the absence of NO3. The disappearance of NO3 was in part accompanied by the formation of N2O5 and HNO3 in the presence of NO2. NO3 uptake performed on small amounts of Kaolinite and CaCO3 led to formation of some N2O5 according to NO3(ads) + NO2(g) –> N2O5(ads) –> N2O5(g). Slow formation of gas phase HNO3 on Kaolinite, CaCO3, Arizona Test Dust and natural limestone has also been observed and is clearly related to the presence of adsorbed water involved in the heterogeneous hydrolysis of N2O5(ads). Uptake of N2O5 on mineral dust samples led to γss values ranging from (3.5 ± 1.1) × 10-2 for CaCO3 to 0.20 ± 0.05 for Saharan Dust with γss decreasing as [N2O5]0 increased. We have observed delayed production of HNO3 upon uptake of N2O5 for every investigated sample owing to hydrolysis of N2O5 with surface-adsorbed H2O. At high and low [N2O5] Arizona Test Dust and Kaolinite turned out to be the samples to produce the largest amount of gas phase HNO3 with respect to N2O5 taken up. In contrast, the yield of HNO3 for Saharan Dust and CaCO3 is lower. On CaCO3 the disappearance of N2O5 was also accompanied by the formation of CO2. For CaCO3 sample masses ranging from 0.33 to 2.0 g, the yield of CO2 was approximately 42 – 50% with respect to the total number of N2O5 molecules taken up. The reaction of N2O5 with mineral dust and the subsequent production of gas phase HNO3 leads to a decrease in [NOx] which may have a significant effect on global ozone decrease. The rate of uptake of ozone on various mineral dust substrates was very similar for all the examined substrates. Both initial and steady state uptake coefficients γ0 and γss were found to be similar for all examined substrates. Uptake experiments on cut marble samples have shown that γ0 and γss based on the geometric and total internal (BET) surface area may be over and underestimated between a factor of 50 to 100, respectively. Based on these considerations we proposed initial and steady state uptake coefficients of the order of 10-4 and 10-5, respectively. For all uptake experiments on mineral dust surrogates, the disappearance of O3 was accompanied by formation of O2. The different mineral dust surrogates may be more accurately distinguished by their time-dependent relative O2 yield rather than the magnitude of γ. The heterogeneous reaction of O3 on mineral dust has been found to be non-catalytic and of limited importance in the atmosphere. Uptake experiments of NO3 on decane flame soot led to a large steady state uptake coefficient γss of 0.2 ± 0.02 for grey and black soot with γss decreasing as [NO3] increased. Adsorbed NO3 led to an uptake of NO2 admitted from the hot NO3 source. On large quantities of grey soot we observed production of HONO (nitrous acid) corresponding to almost 100% of NO2 taken up, whereas no HONO was formed on black soot. The disappearance of NO3 was in part accompanied by the formation of N2O5 according to reaction: NO3(ads) + NO2(ads) –> N2O5(ads) –> N2O5(g) probably due to the presence of adsorbed NO3 on the substrate. Subsequently, hydrolysis of N2O5(ads) with adsorbed H2O led to production of gas phase HNO3. For both grey and black soot we observed production of NO which did not depend of the amount of soot and [NO3]. Decomposition of NO3 and HONO on the soot substrates has been proposed to be responsible of gas phase NO formation

Results of the European Intercomparison exercise for Receptor Models 2011-2012. Part I

Receptor models are commonly used to identify the sources of ambient particulate matter (PM) in Europe. However, the use of different tools and methodological approaches make it difficult to compare the results of different studies. In order to promote harmonization in this field an intercomparison exercise involving 16 expert groups was organized and evaluated by the JRC with the collaboration of European experts in the field. The test database consisted of 178 PM2.5 speciated samples deriving from two real-world re-arranged DB Participants were asked to scrutinize the database in order to identify, solve and report typical imperfections of real world DBs (missing values, values below detection limits, outliers, unusual uncertainty patterns, etc...). The reported solutions included the number and label of the identified sources, their contribution estimation (SCE) and uncertainty. The exercise was evaluated using a new methodology developed on purpose The majority of the solutions reconstructed the PM mass satisfactorily while the number of sources identified in the different solutions was variable. The correspondence of every source/factor to a source category was checked by comparing its chemical profile and time trend with all the other members of the same category and with reference source profiles, when available. The SCEs of the different solutions were compared with a reference value obtained by robust analysis (standard ISO 5725-5). The acceptability criterion was set to 50% standard uncertainty. More than 90% of the 182 tested profiles passed the preliminary tests and 86% of the assessed source/factor contribution estimations met the acceptability criterion. This result indicates a good general agreement between the performances of the different participants and models.JRC.H.2-Air and Climat

The evaluation of the interlaboratory comparison exercise for SO2, CO, O3, NO and NO2 14-17 June 2010

From the 14th to the 17th of June 2010 in Ispra (IT), 9 Laboratories of AQUILA (Network of European Air Quality Reference Laboratories) met at an interlaboratory comparison exercise to evaluate their proficiency in the analysis of inorganic gaseous pollutants covered by European Directive about air quality (SO2, CO, NO, NO2 and O3). The proficiency evaluation, where each participant’s bias was compared to two criteria, provides information on the current situation and capabilities to the European Commission and can be used by participants in their quality control system. On the basis of criteria imposed by the European Commission, 85% of the results reported by AQUILA laboratories were good both in terms of measured values and reported uncertainties. Another 12% of the results had good measured values, but the reported uncertainties were either too high (8%) or too small (4%). Comparability of results among AQUILA participants at the highest concentration level, excluding outliers, is acceptable in NO, CO and O3 measurements while NO2 and SO2 measurement methods showed less satisfactory results.JRC.H.2-Climate change and air qualit

14 th Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes -2-6

Abstract: Receptor Models identify pollution sources by solving a mass balance equation using measured chemical composition of samples in combination with known source profiles. In the last ten years, the number of receptor modelling studies performed on filed air quality data exponentially increased. Among these, 39% are performed with Positive Matrix Factorization (PMF, ME), 23% with Principal Component Analysis (PCA, APCA), 13% with Chemical Mass Balance (CMB), 10% with Factor Analysis (FA, APCFA) and 10% with the APEG model. This approach has been extensively used in North America and South-eastern Asia mainly on particulate matter. Also in Europe it found wide acceptance and contributed to the identification of sources in support of remediation measures design. With the aim of harmonizing the activity in receptor modelling in Europe and supporting the implementation of Directive 2008/50/EC, an evaluation of the current state of this methodology in Europe was carried out highlighting the following needs: improving data collection, harmonizing analytical protocols by setting up common criteria, promoting advanced tools, establishing criteria for the assessment and, comparing receptor model performances. In this study we discuss the sources of uncertainty in the input data and the common approaches used to express them when preparing model input. We also analyze the contribution to the uncertainty deriving from critical model steps and the methodologies used to identify and reduce them. On the basis of the previous discussion we propose a sketch of Common QA/QC protocol. Improving comparability and reliability of receptor models can be achieved by performing inter-comparison exercises. A community-wide inter-comparison organized and evaluated by the JRC within the framework of FAIRMODE is currently in progress. We describe the methodology for the evaluation and comparison of receptor models used in this exercise. Key words: source apportionment, inter-comparison, receptor models, FAIRMODE INTRODUCTION Receptor Models (RM) are used to identify the causes of pollution by analyzing concentrations and other parameters measured at one or more specific sites (receptor). In principle, RM are based on statistical analysis. At the first step they do not consider physical and chemical processes but evolved hybrid models can process additional information to constrain results. Most typical hybrid models are those using wind direction and speed or air masses trajectories to infer the geographical provenience of pollutants

A Methodology to Estimate Functional Vulnerability Using Floating Car Data

In this work, a new methodology to estimate the functional vulnerability of the road network of the city of Catania (Italy) is developed with the purpose to improve the resilience of urban transport during critical events. While the traditional approach for the estimation of vulnerability is based on topological data, the proposed methodology is based on spatial-temporal mobility profiles obtained with floating car data (FCD). The algorithm developed for the estimation of vulnerability combines topological properties of the road network with mobility patterns obtained from FCD to evaluate the consequences of failure events on trajectories and their associated travel times. The core operation of the algorithm is based on the computation of all possible travel paths within their assigned geographical zone every time a road link is disrupted. The procedure may prove useful to evaluate wide failure events and to facilitate emergency plans

Improving Source Apportionment with Receptor Models to Foster the Implementation of the Air Quality Directive

Receptor Models identify pollution sources by solving a mass balance equation using measured chemical composition of samples in combination with known source profiles. In the last ten years, the number of receptor modelling studies performed on filed air quality data exponentially increased. Among these, 39% are performed with Positive Matrix Factorization (PMF, ME), 23% with Principal Component Analysis (PCA, APCA), 13% with Chemical Mass Balance (CMB), 10% with Factor Analysis (FA, APCFA) and 10% with the APEG model. This approach has been extensively used in North America and South-eastern Asia mainly on particulate matter. Also in Europe it found wide acceptance and contributed to the identification of sources in support of remediation measures design. With the aim of harmonizing the activity in receptor modelling in Europe and supporting the implementation of Directive 2008/50/EC, an evaluation of the current state of this methodology in Europe was carried out highlighting the following needs: improving data collection, harmonizing analytical protocols by setting up common criteria, promoting advanced tools, establishing criteria for the assessment and, comparing receptor model performances. In this study we discuss the sources of uncertainty in the input data and the common approaches used to express them when preparing model input. We also analyze the contribution to the uncertainty deriving from critical model steps and the methodologies used to identify and reduce them. On the basis of the previous discussion we propose a sketch of Common QA/QC protocol. Improving comparability and reliability of receptor models can be achieved by performing inter-comparison exercises. A community-wide inter-comparison organized and evaluated by the JRC within the framework of FAIRMODE is currently in progress. We describe the methodology for the evaluation and comparison of receptor models used in this exercise.JRC.H.2-Air and Climat

Enhancing Source Apportionment with Receptor Models to Foster the Air Quality Directive Implementation

Receptor Models (RM) identify pollution sources by solving a mass balance equation using measured chemical composition of samples either in combination with known source profiles or not. This approach has been extensively used in North America and South-eastern Asia mainly on Particulate Matter (PM). In Europe RM found wide acceptance and contributed to the identification of sources in support of remediation measures development. With the aim of harmonizing the activity on receptor modelling in Europe and supporting the implementation of Directive 2008/50/EC, a survey on the use of this methodology was carried out. In this study we discuss the sources of uncertainty in the input data, the common approaches to express uncertainties and their contribution deriving from critical steps. Improving comparability and reliability of receptor models can be achieved by performing intercomparison exercises. We describe the methodology used in an intercomparison exercise organised and evaluated by the JRC within the framework of the Forum for Air quality Modelling (FAIRMODE).JRC.H.2-Air and Climat