
NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
Recipient: |
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Initial Amendment Date: | September 6, 2018 |
Latest Amendment Date: | September 6, 2018 |
Award Number: | 1834711 |
Award Instrument: | Standard Grant |
Program Manager: |
Sylvia Edgerton
sedgerto@nsf.gov (703)292-8522 AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
Start Date: | October 1, 2018 |
End Date: | September 30, 2022 (Estimated) |
Total Intended Award Amount: | $536,373.00 |
Total Awarded Amount to Date: | $536,373.00 |
Funds Obligated to Date: |
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History of Investigator: |
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Recipient Sponsored Research Office: |
201 OLD MAIN UNIVERSITY PARK PA US 16802-1503 (814)865-1372 |
Sponsor Congressional District: |
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Primary Place of Performance: |
617 Walker Building University Park PA US 16802-7000 |
Primary Place of
Performance Congressional District: |
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Unique Entity Identifier (UEI): |
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Parent UEI: |
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NSF Program(s): | Atmospheric Chemistry |
Primary Program Source: |
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Program Reference Code(s): | |
Program Element Code(s): |
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Award Agency Code: | 4900 |
Fund Agency Code: | 4900 |
Assistance Listing Number(s): | 47.050 |
ABSTRACT
This project focuses on laboratory experiments to study the generation of extremely reactive chemical species, known as radicals, that are formed during lightning. An atmospheric radical is a very reactive atom or group of atoms that has the ability to remove or change many pollutants in the atmosphere. The goal of this research is to understand the conditions under which these radicals are produced by lightning and how they influence global and regional atmospheric chemistry. Atmospheric radicals are important because they affect the lifetimes of pollutants and greenhouse gases in the atmosphere.
Laboratory generated electrical sparks and corona over a wide range of conditions will be used to study lightning-generated NOx (LNOx) and lightning-generated HOx (LHOx). The ratio LHOx/LNOx will be measured as will its dependence on: (a) spark intensity, frequency, length, radius, and number; (b) corona intensity and spatial extent; (c) time between generation point and the chemical sensors; (d) the ratio of HOx/NOx production as a function of all of these factors; (e) the relationships among the production of HOx, NOx, and O3; (f) the relationships of the production of HOx, NOx, and O3 to spark and corona characteristics; (g) the influence of pressure, water vapor, and OH reactivity on these relationships and on the calculated OH exposure; and (h) the OH exposure measured by decreases in a volatile organic compound (VOC).
These laboratory measurements will be simulated with photochemical box models to determine the initial HOx/NOx ratio and the resulting OH exposure for comparison with measured values. The information from these laboratory and modeling studies will be parametrized for inclusion in a global chemical transport model, which will be used to understand the global and regional implications of LHOx on atmospheric oxidation.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Lightning is the most powerful and feared of all atmospheric electrical discharges. While best known for striking humans and sparking fires, it is also known to alter the atmosphere?s chemical composition by producing nitric oxide (NO) and nitrogen dioxide (NO2) in lightning hot channel cores. In this research we demonstrate that essentially all electrical discharges directly generate prodigious amounts of hydroperoxyl (HO2) and hydroxyl (OH) and that all OH generated outside of lightning hot channel cores will contribute to atmospheric cleansing (Figure 1).
A combination of field studies, laboratory experiments, and modeling support this conclusion. Flights through electrified anvil clouds of thunderstorms during the 2012 Deep Convective Clouds and Chemistry (DC3) study found periods where OH and HO2 amounts were hundreds to thousands times larger than normal. Much of this prodigious OH and HO2 was linked to electrical flashes detected by ground-based lightning mapping arrays viewing the same clouds, but not all. Laboratory studies demonstrated that much weaker unseen discharges, called subvisible discharges, also generate prodigious OH and HO2. It is known that electrified thunderstorms contain electrical discharges with a range of energies, which implies frequent and widespread prodigious HO2 and OH generation in thunderstorms.
Our laboratory studies demonstrated several features of spark-generated atmospheric reactive chemicals. First, the mixing ratios of OH, HO2, NO, NO2, and ozone (O3) are independent of pressure, meaning that higher concentrations are generated near Earth's surface than at airline-cruising altitudes of 8-12 km. Second, mixing ratios of OH and HO2 have a weak dependence on water vapor while the mixing ratio of NO has none. Third, the observed lifetime of OH generated by sparks, which is tenths of seconds, is greater than the modeled lifetime, which is microseconds because the OH and HO2 are consumed by nitrogen oxides in the hot spark core. This large difference indicates that OH and HO2 are being generated outside of the hot spark core, separate from the NO. Fourth, OH and HO2 are generated in equal amounts. From all these features, we conclude that OH and HO2 are generated by the simple dissociation of water vapor, which splits into OH and H, which rapidly reacts with O2 to form HO2. Thus, even weak electrical discharges produce prodigious OH and HO2.
This research then focused on ground-based sources of electrical discharges, starting with unexplained large spikes in OH and HO2 measured under thunderstorms during a 2006 air quality study in Houston, TX. The instrument was the same one used to measure OH and HO2 in the thunderstorm anvil clouds during DC3 and was mounted on the roof of an 18-story building. OH and HO2 amounts, hundreds to thousands times larger than normal, were observed for the seven times thunderstorms passed directly over the site and at no other times. Analysis of the spikes indicated that they were likely produced by corona electrical discharges on the upward facing metal instrument inlet itself. However, laboratory studies demonstrated that corona form more easily on lightning rods than on the instrument inlet, indicating that OH and HO2 are likely being generated by corona on many pointy conductive grounded objects under thunderstorms.
Observations have been reported of corona electrical discharges formed on tree leaves under thunderstorms, although the atmospheric corona characteristics have rarely been quantified. In the laboratory, tree leaves were subjected to constant high voltages to produce corona and the generated OH, HO2, O3, and NO were measured for different environmental and electrical conditions. The corona and the generation of OH and HO2 varied for eight tree leaf types, for the high voltage polarity (Figure 2) and for the leaf dryness. However, the OH and HO2 generation correlated with the corona ultraviolet flux, independent of all these other factors.
Estimates were made of the range of impacts for these different types of electrical discharges. In all cases, the atmospheric observations are few so that these estimates have large uncertainties. For the electrical discharges in the thunderstorm clouds, the 1800 thunderstorms occurring every second globally could produce as much as 2% to 16% of the total known global OH, a quite significant number that may increase as climate changes. For the corona on pointy grounded metal objects and the tree leaves under thunderstorms, OH levels and their chemical effects are a few orders of magnitude larger than normal near the corona, potentially affecting nearby materials and the trees. For corona that form on high voltage electrical power transmission lines and equipment, the prodigious OH and its effects can spread several meters into the surrounding areas, and, perhaps more importantly, prematurely degrade electrical insulating material. All these effects have societal implications. The large uncertainties in all these estimates can be reduced only by more atmospheric observations.
Last Modified: 01/07/2023
Modified by: William H Brune
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