High-resolution hybrid inversion of IASI ammonia columns to constrain US ammonia emissions using the CMAQ adjoint model

Ammonia (NH3) emissions have large impacts on air quality and nitrogen deposition, influencing human health and the well-being of sensitive ecosystems. Large uncertainties exist in the "bottom-up" NH3 emission inventories due to limited source information and a historical lack of measurements, hindering the assessment of NH3-related environmental impacts. The increasing capability of satellites to measure NH3 abundance and the development of modeling tools enable us to better constrain NH3 emission estimates at high spatial resolution. In this study, we constrain the NH3 emission estimates from the widely used 2011 National Emissions Inventory (2011 NEI) in the US using Infrared Atmospheric Sounding Interferometer NH3 column density measurements (IASI-NH3) gridded at a 36 km by 36 km horizontal resolution. With a hybrid inverse modeling approach, we use the Community Multiscale Air Quality Modeling System (CMAQ) and its multiphase adjoint model to optimize NH3 emission estimates in April, July, and October. Our optimized emission estimates suggest that the total NH3 emissions are biased low by 26 % in 2011 NEI in April with overestimation in the Midwest and underestimation in the Southern States. In July and October, the estimates from NEI agree well with the optimized emission estimates, despite a low bias in hotspot regions. Evaluation of the inversion performance using independent observations shows reduced underestimation in simulated ambient NH3 concentra- tion in all 3 months and reduced underestimation in NH4 wet deposition in April. Implementing the optimized NH3 emission estimates improves the model performance in simulating PM2.5 concentration in the Midwest in April. The model results suggest that the estimated contribution of ammonium nitrate would be biased high in a priori NEI-based assessments. The higher emission estimates in this study also imply a higher ecological impact of nitrogen deposition originating from NH3 emissions.

Understanding the origins and fate of air pollution in Bogota, Colombia

Erika Maria Zarate Torres

Bogota has more than 8 million inhabitants and is the 5th biggest urban agglomeration in Latin America. It has more than one million vehicles and a large number of small industries. High levels of air pollutants are thus detected. The purpose of this work consists in applying air quality modelling tools to the region of Bogota, aiming to acquire a deeper understanding of the factors that originate air pollution in the city, and of the way pollutants are dispersed and chemically transported. Furthermore, the knowledge gained is used to propose and evaluate air pollution abatement strategies. In the first part of this thesis, two versions of the traffic emission inventory are generated, one using standard CORINAIR traffic emission factors and the other using bulk real-world traffic emission factors. Both emission inventories are compared and evaluated with the help of numerical simulations. The emission inventory calculated using bulk real-world traffic emission factors generates simulated concentrations closer to the observed values. Thus, an innovative technique consisting in the combination of measurements and modelling to estimate and evaluate traffic emissions is proposed in this part of the study. In the second part, mesoscale meteorological and air quality models are applied to the city. The wind pattern developed over the complex topography of the region and the development of the plume of pollutants are simulated with success. In the third part of this work, the air quality model is used to study the plume of pollution in terms of the governing chemical regimes and the individual and combined effects of the main sources of emission. Traffic is the major contributor to the plume of pollutants in Bogota. Three feasible emission scenarios which are addressed to the mitigation of emissions from heavy traffic are evaluated with the model. Whereas reductions are attained for primary pollutants and aerosols (whose simulation is presented in the forth part of this work), levels of Ozone increase with these scenarios. The air quality model indicates that strategies directed to mitigate air pollution might have contradictory effects depending on the pollutant to be tackled. Air quality modelling proved to be a very useful tool for evaluating emission scenarios in advance and prioritizing actions to mitigate pollution in Bogota.

EPFL2007

Air quality modelling over Bogota, Colombia: Combined techniques to estimate and evaluate emission inventories

Luis Carlos Belalcazar Ceron, Alain Clappier, Hubert van den Bergh, Erika Maria Zarate Torres

Two versions of the Emission Inventory (EI) are generated for the city of Bogota, Colombia. In the first version (EI-1), CORINAIR traffic emission factors (EFs) are used. In the second (EI-2), bulk traffic EF's calculated for the city, using in situ measurements and inverse modelling techniques at street level, are used. EI-2 traffic emissions are 5, 4 and 3 times bigger than the corresponding values in EI-1, for CO, PM10 and NMVOCs, respectively. The main goal of this study consists in evaluating the two versions of the El when introduced into a mesoscale air quality model. The AOT (accumulated exposure over a threshold) index is calculated for comparison between observed and simulated concentrations of primary pollutants. Simulated concentrations using EI-2 are closer to the observed values. This comparison allows us to extract some conclusions of the methodology used to calculate the EFs. Local factors like the driving behavior, the altitude, vehicle technology and an aged fleet cannot be totally included and corrected in the standard methodologies, and seem to be more important than obtaining very detailed and precise information on the classification of the fleet or driving speeds. Under financially limited and fast changing situations, as in the case of many developing countries, a simple methodology to estimate bulk traffic Ef's and to evaluate the Ell, is of utmost importance. The use of combined techniques such as in situ measurements to estimate bulk traffic EFs, and further evaluation of the inventories with numerical models, proved to be a useful too] for this purpose. (c) 2007 Elsevier Ltd. All rights reserved.

2007

Understanding the origins and fate of air pollution in Bogota, Colombia

Erika Maria Zarate Torres

EPFL2007