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Formation of nitrous acid on urban surfaces [Elektronische Ressource] : a physical-chemical perspective / presented by Sebastian Trick

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Dissertation submitted to the Combined Faculties for the Natural Science and for Mathematics of the Ruperto Carola University Heidelberg, Germany for the degree of Doctor of Natural Science presented by: Sebastian Trick born in Heilbronn oral examination: 21.07.2004 Formation of Nitrous Acid on Urban Surfaces - a physical-chemical perspective Referees: Prof. Dr. Ulrich Platt Prof. Dr. Ulrich Schurath Abstract Nitrous acid (HONO) has been observed in the nocturnal urban atmosphere for decades. During daylight hours, the rapid photolysis of HONO is a significant source of OH-radicals, which drive tropospheric chemistry and ozone-formation. Recently, unexpected high values of HONO have been detected during the day. Despite its importance, sources of HONO are still poorly understood. Direct emission of HONO or homogeneous chemical formation alone cannot explain the high HONO-to-NO 2ratios often measured in the boundary layer. Today it is thus generally accepted that HONO is formed by heterogeneous hydrolysis of NO . However, large uncertainties about the nature of the surfaces and 2the chemical conversion mechanism remain. Here, we present direct measurements from three field campaigns detecting daytime HONO mixing ratios of ~200 ppt using DOAS. A chemical transport model (RCAT 8.1.

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Published 01 January 2004
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Dissertation
submitted to the
Combined Faculties for the Natural Science and for Mathematics
of the Ruperto Carola University Heidelberg, Germany
for the degree of
Doctor of Natural Science



















presented by:

Sebastian Trick
born in Heilbronn


oral examination: 21.07.2004



Formation of Nitrous Acid on Urban Surfaces
-
a physical-chemical perspective























Referees: Prof. Dr. Ulrich Platt
Prof. Dr. Ulrich Schurath

Abstract

Nitrous acid (HONO) has been observed in the nocturnal urban atmosphere for decades. During
daylight hours, the rapid photolysis of HONO is a significant source of OH-radicals, which drive
tropospheric chemistry and ozone-formation. Recently, unexpected high values of HONO have been
detected during the day. Despite its importance, sources of HONO are still poorly understood. Direct
emission of HONO or homogeneous chemical formation alone cannot explain the high HONO-to-NO 2
ratios often measured in the boundary layer. Today it is thus generally accepted that HONO is formed
by heterogeneous hydrolysis of NO . However, large uncertainties about the nature of the surfaces and 2
the chemical conversion mechanism remain.
Here, we present direct measurements from three field campaigns detecting daytime HONO mixing
ratios of ~200 ppt using DOAS. A chemical transport model (RCAT 8.1.2) was modified to quantify
the individual contribution of the vertical transport effects and chemical processes for different times
of the day. While aerosols were found to be of minor importance under all circumstances, vertical
transport and heterogeneous HONO production on the ground surface (at ~5%) and on canopies (at
~45%) were found to be of major influence on the daytime production of atmospheric HONO.
The heterogeneous interactions of HONO with real urban surfaces were further investigated in a smog
chamber using a White-type DOAS multi-reflection system. The NO uptake coefficients on these 2
-8 -7 -5surfaces were calculated to be γ ~10 on Teflon, ~10 on PE foil, ~10 on asphalt and concrete, ~3 NO2
-6 -5x 10 on roof-tiles and flagstone-tiles, and ~2 x 10 on grass. The higher values were found to be well
correlated to an enhanced BET surface. The HONO concentrations were found to scale with the
relative humidity, and thus the HONO uptake coefficient is not independently determinable.
Therefore, a model (HeCSI) was developed using Langmuir adsorption-desorption isotherms to
describe the concentration-time series of all trace gases. Based on this new model approach, HONO
uptake coefficients, the amount of HONO adsorbed on the surfaces of the smog chamber, and the out-
gassing frequency could be determined. It was found that the physical-chemical equilibrium
underlying the model describes the chemical NO - system at all times X

Zusammenfassung

Salpetrige Säure (HONO) wird seit Jahrzehnten in der nächtlichen urbanen Atmosphäre beobachtet.
Am Tage stellt ihre rasche Photolyse eine bedeutende Quelle des OH-Radikals dar, das die
troposphärische Chemie und Ozonbildung katalysiert. In jüngster Zeit werden hohe HONO -
Messwerte auch am Tages gefunden. Neben dieser atmosphärischen Bedeutung der HONO, sind ihre
Quellen nur wenig verstanden. Direkte Emissionen und homogene Reaktionen können für sich nicht
die häufig in der PBL gemessenen HONO-zu-NO Verhältnisse erklären. Es gilt heute als gesichert, 2
dass HONO aus der heterogenen Hydrolyse von NO entsteht. Jedoch bestehen dabei enorme Un-2
sicherheiten betreff der Beschaffenheit der Oberfläche und des Mechanismus der chemischen
Umwandlung.
In dieser Arbeit wurden während dreier Feldmesskampagnen HONO - Tageswerte ~200 ppt mit
DOAS gemessen. Ein Chemie-Transport Model (RCAT 8.1.2) wurde modifiziert, um die einzelnen
Beiträge von Vertikaltransport und chemischen Prozessen tageszeitabhängig zu quantifizieren.
Während danach Aerosole nur einen vernachlässigbaren Einfluss auf die atmosphärischen HONO
Konzentrationen unter nahezu allen Bedingen auszuüben scheinen, beeinflussen die vertikale
Mischung, die heterogenen Reaktionen am Boden (dort zu ~5%) und besonders an Hauswänden (zu
~45%) enorm die Bilanz von HONO am Tage.
Die heterogenen Wechselwirkungen von HONO mit realen urbanen Oberflächen wurden in einer
Smogkammer mittels eines DOAS White-Vielfachreflexionssystem untersucht. Die NO uptake 2
-8 -7Koeffizienten für verschiedene Oberflächenarten wurden berechnet: γ ~10 auf Teflon, ~10 auf NO2
-5 -6 -5PE Folie, ~10 auf Asphalt und Beton, ~3 x 10 auf Dach- und Keramikfließen und ~2 x 10 auf
Gras. Diese erhöhten Werte konnten durch eine vergrößerte BET Oberfläche erklärt werden. Die
HONO - Konzentrationen wurden korreliert mit der relativen Luftfeuchte beobachtet, so dass HONO
uptake Koeffizienten nicht analytisch bestimmbar sind. Daher wurde ein Model (HeCSI) entwickelt,
das die Langmuir Absorptions-Desorptions-Isotherme nutzt, um die Konzentrationszeitreihen aller
Spurenstoffe gleichzeitig zu beschreiben. Mit diesem neuen Modellansatz konnten die HONO uptake
Koeffizienten, die Menge der an den Wänden der Smogkammer absorbierten HONO und dessen
Ausgasrate ermittelt werden. Weiter konnte gezeigt werden, dass mittels dieses physikalischen-
chemische Gleichgewichts, das dem Model zugrunde liegt, das chemische NO -Reaktionssystem zu x
jeder Zeit beschreibbar ist.

Table of Content i
Table of content
1 Introduction 1
2 Theoretical Background:
Chemistry and Physics of the Lower Troposphere 5
2.1 Tropospheric Nitrogen Oxides 6
2.1.1 Sources and Sinks of Tropospheric Nitrogen Oxides 6
2.1.2 Overview of Tropospheric NO Chemistry 11 y
2.2 Photochemical Reactions 13
2.2.1 The Photo-Stationary Steady State & Leighton Ratio 13
2.2.2 Deviations from the Leighton Ratio & the Formation of Photosmog 14
2.2.3 The Origin of the Tropospheric OH Radicals 15
2.3 Nitrous Acid (HONO) 18
2.3.1 Importance of Atmospheric HONO 18
2.3.2 Diurnal Variation of HONO in the Troposphere 19
2.3.3 Direct Emission Sources of Nitrous Acid 21
2.3.4 Homogeneous Formation of Nitrous Acid 23
2.3.5 Heterogeneous Formation of Nitrous Acid 25
2.3.5.1 The Disproportionation of NO 25 x
2.3.5.2 Direct Reduction on Fresh Soot 26
2.3.5.3 Further Heterogeneous Reactions yielding HONO 26
2.3.5.4 Photolytic Enhancement of HONO Formation 27
2.3.6 HONO Formation by Heterogeneous Dispropotionation of NO 28 2
2.3.6.1 Formation of Nitrous Acid on Airborne Particles (Aerosols) 28
2.3.6.2 s Acid on Macroscopic Surfaces & on the Ground 30
2.3.6.3 Evidence for a ground-near Source by Vertical Gradients of HONO 31
2.3.6.4 Kinetics & Water Dependence of HONO Formation 33
2.3.6.5 Mechanistic Sequences of Heterogeneous HONO Formation 35
2.3.7 Sinks of Atmospheric Nitrous Acid 38
2.4 Heterogeneous Reactions and Catalysis 40
2.4.1 Heterogeneous Catalysis 40
2.4.2 Adsorption and Desorption of Gases on a Solid Surface 42
2.4.2.1 Possibilities of Gas-Phase to Solid-Surface Interactions 42
2.4.2.2 Energetic Aspects of Adsorption and Desorption 44
2.4.3 Thermodynamic and Kinetic Considerations 46
2.4.3.1 Empirical Aspects on Thermodynamics 46
2.4.3.2 Mathematical Description of Adsorption 47
2.4.3.3 Description of Kinetic of Desorption 49
2.4.4 Derivation and Applications of Adsorption Isotherms 49
2.4.4.1 The Langmuir Adsorption-Desorption Isotherms 49
2.4.4.2 Kinetic of Heterogeneously (Catalyzed) Reactions 50
2.4.4.3 Other Adsorption Isotherms: BET Theory 51 Table of Content ii
2.5 Basics of Atmospheric Dynamics of the Boundary Layer 54
2.5.1 The Structure of the Planetary Boundary Layer 54
2.5.1.1 The Laminar Surface Layer 54
2.5.1.2 The Prandtl Layer 55
2.5.1.3 The Ekman Layer 55
2.5.1.4 The Height of the PBL 55
2.5.2 Diurnal Variations of the PBL: Micrometeorological Description 56
2.5.3 Transport Processes in the PBL: The Friction Velocity 58
2.5.3.1 Neutral Layering 59
2.5.3.2 Labile and Stable Layering 60
2.5.4 Radon as a Tracer for Mixing in and the Height of the PBL 62
3 Measurement Methods 65
3.1 Overview of Detection Techniques for Nitrous Acid 65
3.1.1 Chemical Surface Collection Techniques 65
3.1.1.1 The Denuder Technique 66
3.1.1.2 Chemiluminescence Detection 68
3.1.1.3 The DNPH-HPLC Method 69
3.1.1.4 The LOPAP Instrument 69
3.1.2 Mass Spectrometry 70
3.1.3 Spectroscopic Methods 71
3.1.3.1 UV – PF / LIF - Sensor 71
3.1.3.2 IR – Spectroscopy 71
3.2 Differential Optical Absorption Spectroscopy 72
3.2.1 An Overview of DOAS Applications 72
3.2.2 Theoretical Description of DOAS 73
3.2.2.1 Basic Theory of Absorption Spectroscopy & Lambert-Beers Law 73
3.2.2.2 DOAS for Atmospheric Measurements: Numerical Description 77
3.2.2.3 The Analysis Procedure 79
3.2.2.4 Error Estimation 81
3.2.2.5 Effects of Residual Structures: X-Absorber and Detection Limit 81
3.2.3 Instrumental Setup of a DOAS System 82
3.2.3.1 The Long Path (LP) DOAS System 82
3.2.3.2 The DOAS White Multi-Reflection System 84
3.2.3.3 The Light Source 87
3.2.3.4 The Spectrograph 87
3.2.3.5 The Detector 88
3.2.3.6 Characterization of the Detector Unit 89
3.2.3.7 The Quartz Fiber Mode Mixer 91
3.2.4 Performing HONO Measurements by DOAS 91
3.2.4.1 The Measurement Algorithm for HONO 91
3.2.4.2 Reference Spectra for the DOAS Evaluations 93
3.2.4.3 Evaluation of LP-DOAS Data 94
3.2.4.4 n of White-DOAS Data 96
4 Field Studies and Results 99
4.1 The Rome 2001 field campaign:
Detection of Daytime HONO 99
4.1.1 The Area of Rome 99 Table of Content iii
4.1.2 Measurements in the City Center of Rome 101
4.1.2.1 Instrumental Setup of the LP-DOAS 101
4.1.2.2 Trace Gas Measurements in the City Center of Rome 102
4.1.2.3 Radiance Data 104
4.1.2.4 Aerosol Particles 105
4.1.3 The Villa Ada Background Measurement Station 107
4.1.3.1 The HONO Measurements at Villa Ada 107
4.1.3.2 Intercomparison of HONO Measurement Techniques 108
4.1.3.3 Additional Trace Gases measured at Villa Ada 109
4.1.3.4 Natural Radioactivity Measurements and Meteorology 109
4.1.4 The Measurements in Montelibretti 110
4.1.4.1 Setup of the LP-DOAS System 111
4.1.4.2 Trace Gas Measurements in Montelibretti 111
4.1.4.3 Additional Measurements in Montelibretti 113
4.1.5 Intercomparison between Rome and Montelibretti Trace Gas Data 114
4.1.6 Photochemical Smog Events 114
4.1.6.1 The Smog Event on 31.05.2001 115
4.1.6.2 Pollution Event on 24.05.2001 116
4.1.7 Qualitative Correlations of HONO and Radon Data 117
4.1.7.1 HONO-Time-Derivative by Vertical Mixing of the PBL 118
4.1.7.2 Influence of Atmospheric Stability on Daytime HONO Values 121
4.2 The Format 2002 campaign:
Intercomparison of Trace Gas Measurements 123
4.2.1 The Measurement Location 123
4.2.2 DOAS Measurements at Bresso 124
4.2.2.1 Setup of the DOAS White-Multi-Reflection System 124
4.2.2.2 Measurement of Trace Gases in Bresso 125
4.2.3 Additional Equipment at Bresso 127
4.2.3.1 In-situ Trace Gas Measurements 127
4.2.3.2 Radiance Data 127
4.2.3.3 Aerosol Particles 128
4.2.3.4 Meteorological Data at Bresso 128
4.2.4 Intercomparison of HONO Measurements 129
4.3 The Turm 2003 campaign:
Vertical Profiles of HONO 131
4.3.1 The Area of the FZ Karlsruhe and the Meteorological Tower 131
4.3.1.1 The location of the Forschungszentrum Karlsruhe 131
4.3.1.2 The Meteorological Tower 131
4.3.2 The Active Long Path DOAS System 133
4.3.3 Retrieval of trace gas profiles from LP-DOAS data 135
4.3.3.1 Deconvolution of Temporal and Spatial Information 135
4.3.3.2 Error Estimation and Limitations of the DOAS Vertical Profiles 136
4.3.3.3 Calculation of Vertical Gradients 137
4.3.4 Additional Equipment and cooperating groups 138
4.3.4.1 Ozone Measurements 138
4.3.4.2 The Radiance Data 138
4.3.4.3 Natural Radon Activity and Atmospheric Dynamic 138
4.3.4.4 In-situ Instruments of cooperating groups at the Tower 139
4.3.5 Time Series of Traces Gases 140
4.3.5.1 Temporal Trends of O and HCHO 140 3
4.3.5.2 Time Series of HONO, and NO in Different Altitudes 140 2
4.3.5.3 The Altitude Dependent HONO-toNO ratio 142 2Table of Content iv
4.3.6 Nighttime Vertical Gradients of the Trace Gases 144
4.3.6.1 NO Gradients 144 2
4.3.6.2 HONO Gradients 146
4.3.6.3 The HONO-to-NO Ratio 146 2
4.3.6.4 O and NO Gradients 148 3
4.3.7 Influence of Vertical Transport in the PBL on Gradients 148
4.3.8 Temporal Trends of Vertical Gradients 149
4.3.9 Daytime Gradients of the Trace Gases 152
5 The Smog Chamber Studies:
Heterogeneous HONO Formation 153
5.1 Experimental Setups 154
5.1.1 The Smog Chamber 154
5.1.1.1 Characteristics of the Gas Supply 155
5.1.1.2 The Leakage of the Smog Chamber 156
5.1.1.3 Mixing and Homogeneity of the Smog Chamber 156
5.1.1.4 Humidification of the Smog Chamber 157
5.1.2 Generation of the Injected NO 157 2
5.1.3 The Investigated Surfaces 157
5.1.4 The Measurement Techniques 159
5.1.4.1 The DOAS White System inside the Smog Chamber 159
5.1.4.2 Additional Measurements during the IUP 2002 campaign 160
5.1.4.3 Measurement Equipment during the KIP 2003 campaign 160
5.2 Results of the Experiments 161
5.2.1 Experiments on Teflon and PE Surface 164
5.2.2 s on Real Urban Surfaces 166
5.2.3 Experiment of HONO Formation on Grass 168
5.3 Analysis of NO Decays 169 2
5.3.1 Calculation of the NO Uptake Coefficients 169 2
5.3.2 Dependence of the NO Uptake Coefficients on R.H. 172 2
5.4 Analysis of HONO in the Smog Chamber 174
5.4.1 Dependence of HONO Yield on NO 174 2
5.4.2 Dependence of HONO on Relative Humidity 176
5.5 Analysis of NO Chemistry in the Smog Chamber: x
Modeling Studies 179
5.5.1 Modifications of Langmuir Theory for HONO 179
5.5.2 Description of the Model 181
5.5.3 The Mechanism of the NO Chemistry in the Smog Chamber 183 x
5.5.3.1 Modeled NO Chemistry 183 2
5.5.3.2 Chemistry of Surface Adsorbed Species 184
5.5.3.3 Modeled Time Series of HONO 186
5.5.3.4 Secondary Reactions yielding NO 187
5.5.4 Sensitivity Studies of the HeCSI Model 189
5.5.5 Model Results for the different Surface Types 191

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