Mid-Atlantic Section Fall Meeting 2020
Volume 65, Number 20
Friday–Sunday, December 4–6, 2020;
Virtual
Session F03: Atmospheric Chemistry, Physics and Aerosols II
2:00 PM–4:00 PM,
Saturday, December 5, 2020
Chair: Daniel Knopf
Abstract: F03.00003 : Mid-infrared sensing of atmospheric ammonia: linking farms, cities, and ecosystems
3:12 PM–3:48 PM
Preview Abstract
Abstract
Author:
Mark Zondlo
(Dept. of Civil and Environmental Engineering, Princeton University)
Atmospheric ammonia - the most important base in the atmosphere - degrades
the environment through the formation of unhealthy particulate, nitrogen
deposition in sensitive ecosystems, and scattering of visible light for
climate and visibility impacts. Despite its global importance, ammonia is a
challenging measurement to make. Ammonia readily sticks to instrument
surfaces such as inlets or sample cells, its atmospheric mole fraction is
low (parts per trillion to parts per billion by volume), and it can readily
partition between gas phase ammonia and particulate phase ammonium. I will
discuss field measurements with open-path, quantum cascade laser-based
sensors that have been deployed in field campaigns across the world to
understand the spatiotemporal variabilities of its atmosphere-surface
fluxes. The open-path configuration - where the sampled air is passively
sampled between mirrors of a Herriott cell without actively going through
tubing, inlets, or sample manifolds - allows for fast (25 Hz), sensitive (30
pptv), and accurate (20{\%}) measurements to deduce rapid changes in fluxes
on platforms such as mobile laboratories, tall towers, and aircraft. The
sensor consumers 45 W of power for ease of deployment in power-constrained
environments such as in remote settings of agricultural fields or natural
ecosystems. Vehicle emissions of ammonia from real-world driving
measurements across 5 cities in the United States are twice as high as the
EPA National Emissions Inventory, suggesting an important urban emission
source that is co-located with emissions of nitrogen and sulfur oxides.
Agricultural sources in both Colorado and California show large
spatiotemporal variabilities including diurnal, seasonal, and farm-to-farm
differences. Agricultural emissions, when combined with new satellite
ammonia measurements, in-situ measurements, and ecosystem flux measurements,
show significant effects on downstream air quality in cities and nitrogen
deposition in remote ecosystems.