Advances in Atmospheric Chemistry

Volume 2: Organic Oxidation and Multiphase Chemistry

Philip Kotler, Hermawan Kartajaya;Den Huan Hooi

• Publisher: WSPC
• eBook ISBN: 9789813271845
• Topic: Physical Sciences
• Subtopic: Environmental Science

Asia is the most populated geographical region, with 50% of the world's inhabitants living there. Coupled that with the impressive economic growth rates in many Asian countries, the region provides a very attractive and lucrative market for many busine

Chapter 1

Atmospheric Ammonia: Measurements, Modeling, and Chemistry–Climate Interactions

A. G. Tevlin* and J. G. Murphy

Department of Chemistry, University of Toronto,
80 St. George Street, Toronto, Canada, M5S 3H6
*[email protected]

Global concentrations of atmospheric ammonia have greatly increased due to anthropogenic activities, with significant impacts on human and ecosystem health and the global radiative budget. Difficulties in measuring and modeling this molecule, however, mean that many aspects of the processes governing its sources and sinks are not well understood. Future changes in climate will only exacerbate these uncertainties. The effects of climate change on the concentration and environmental fate of ammonia are inextricably linked with the effects of ammonia on a changing climate in ways that are complex, nonlinear, and poorly constrained. These uncertainties are increased by the often opposing influences of specific effects. Increasing temperature, for example, is expected to increase ammonia emissions, while also promoting partitioning of ammonium from the particle to the gas-phase. The resulting impact on atmospheric aerosols, and thus on negative radiative forcing will depend on the relative strengths of these processes. The net effect of climate change is expected to be an increase in atmospheric ammonia. Both the direction and magnitude of the net effect of ammonia on climate, however, are unclear. More direct analyses of these interactions are needed to determine the most effective mitigation strategies.

1.1.Introduction

1.1.1.Importance of Ammonia

Increases in fertilizer-driven industrial agriculture have led to a significant rise in total global reactive nitrogen (N_r) from preindustrial times to the present.^1–7 Losses of fertilizer ammonia (NH₃) and ammonium

have caused an overall increase in total NH_x

in soils and surface water as well as in the atmosphere in both gas- and particle-phases. The consequences of these changes come in several forms, including through changes in N_r deposition to nonfertilized ecosystems and changes in the formation and growth of atmospheric particles.

Enhanced deposition of reactive nitrogen contributes to the eutrophication of sensitive ecosystems.^8,9 Ecosystems exposed to higher concentrations of N_r can also experience acidification via nitrification.^8–14 In many regions, NH₃ is the greatest contributor to N_r deposition.^15,16 Additionally, N_r deposited in the form of NH₃ or

is thought to be more bioavailable, and therefore to have a greater impact on the eutrophication of sensitive ecosystems than other more oxidized forms.¹⁷

NH₃ also plays a role in determining the total mass, number concentration, and extent of neutralization of atmospheric particles.^18–21 The contribution of

to particulate matter (PM) in recent decades is approximately 0.47 Tg, or 14% of total mass on a global basis.²² For comparison, this mass contribution is only about one-third of that from non-sea salt sulfate (nss-

), but close to that of nitrate

.²³ Modeling studies, as well as ice core records, suggest that

particle loadings have increased since preindustrial times both in absolute terms, and in their relative contributions to particle mass.^6,23 The nucleation rate of aerosol particles from the condensation of sulfuric acid vapor has been shown to increase significantly in the presence of NH₃.^19,24,25 Once these particles grow beyond the nucleation stage, gas-particle partitioning of NH₃ to form

salts can contribute to their continued growth. The low vapor pressure of solid ammonium sulfate [(NH₄)₂SO₄] makes its formation essentially irreversible.²⁶ Being more volatile, ammonium nitrate (NH₄NO₃) and ammonium chloride (NH₄Cl) rely on the presence of NH₃ to draw gas-phase nitric acid (HNO₃) and hydrochloric acid (HCl) into the particles. Because of this, their mass loading will depend greatly on the amount of available NH₃.^27,28

PM has important consequences for human health. Several studies have found correlations between PM exposure and cardiopulmonary mortality, as well as hospital admissions and other indicators of negative health effects.^29–35 The severity of these effects have been seen to depend on the degree to which particles have been neutralized by NH₃.³⁶ PM also has important impacts on the Earth’s climate. Aerosol particles impact the global radiative budget directly by scattering incoming radiation, and indirectly by acting as condensation nuclei for cloud formation, thereby increasing the reflectivity and lifetime of clouds. Because of the nonlinearity of these processes, the negative radiative forcing due to aerosols contributes the largest source of uncertainty to the net radiative forcing from anthropogenic influences.^37,38 The relatively short atmospheric lifetimes of particles mean that changes in their sources will alter concentrations relatively quickly and their distribution is likely to be more heterogeneous than longer-lived greenhouse gases (GHGs). Their climate impacts may therefore be more significant at the regional level than global averages might suggest.³⁹ The extent of neutralization of particles by NH₃ can alter their hygroscopicity,⁴⁰ as well as the reactions occurring both within them and on their surfaces.⁴¹

Given their impacts on human and ecosystem health, regulatory efforts have been introduced in many countries to limit emissions of inorganic particle precursors. Restrictions on emissions of nitrogen oxides (NO_x = NO + NO₂) and sulfur dioxide (SO₂) in Europe and North America have proven to be quite effective.^42,43 Less effort has been made to decrease emissions of NH₃, despite work showing the potential benefits to human health of such actions.^44–46 On the contrary, in many parts of the world, unregulated NH₃ emissions have been growing along with increasing fertilizer use and livestock populations, a trend that is expected to continue.⁴ Several countries have suggested critical levels of NH_x above which negative ecosystem impacts can be expected. These range from annual averages of 1–8 μgm^–3. Despite these concerns, few countries have introduced legislation to reduce concentrations below these levels.^42,47–49 One exception to t...

Table of contents

• Cover
• Halftitle
• Series Editors
• Title
• Copyright
• Volume 2. Editorial Advisory Board
• Preface
• Contents
• List of Contributors
• 1. Atmospheric Ammonia: Measurements, Modeling, and Chemistry—Climate Interactions
• 2. Atmospheric Heterogeneous and Multiphase Chemistry and Its Implications for Air Pollution in China
• 3. Advances in Identification and Quantification of Non-methane Volatile Organic Compounds Emitted from Biomass Fires through Laboratory Fire Experiments
• 4. Gas-Phase Organic Oxidation Chemistry and Atmospheric Particles
• 5. New Insights into the Role of Stabilized Criegee Intermediates in Tropospheric Chemistry from Direct Laboratory Studies
• 6. Reaction Mechanisms for the Atmospheric Oxidation of Monocyclic Aromatic Compounds
• 7. The Effects of Stratospheric Chemistry and Transport on the Isotopic Compositions of Long-Lived Gases Measured at Earth’s Surface
• Index