3 research outputs found
Liquid-Desiccant Vapor Separation Reduces the Energy Requirements of Atmospheric Moisture Harvesting
An
innovative atmospheric moisture harvesting system is proposed,
where water vapor is separated from the air prior to cooling and condensation.
The system was studied using a model that simulates its three interconnected
cycles (air, desiccant, and water) over a range of ambient conditions,
and optimal configurations are reported for different operation conditions.
Model results were compared to specifications of commercial atmospheric
moisture harvesting systems and found to represent saving of 5–65%
of the electrical energy requirements due to the vapor separation
process. We show that the liquid desiccant separation stage that is
integrated into atmospheric moisture harvesting systems can work under
a wide range of environmental conditions using low grade or solar
heating as a supplementary energy source, and that the performance
of the combined system is superior
Night-Time Ground Hyperspectral Imaging for Urban-Scale Remote Sensing of Ambient PMî—¸Modal Concentrations Retrieval
Retrieval
of aerosol loading in vertical atmospheric columns is
a common product of satellite and ground instruments that measure
spectral extinction of solar radiation throughout the entire atmosphere.
Here we study ground hyperspectral imaging of artificial light sources
as a complementary method for retrieving fine aerosol concentrations
along quazi-horizontal ambient open paths. Previously, we reported
hyperspectral measurements of the aerosol optical thickness in the
500–900 nm range over urban-scale distances (180 m to 4 km),
measuring the extinction of radiation emitted from a halogen source.
Here we confirm in a laboratory-setup the basic premise that different
accumulation-size aerosols generate distinct hyperspectral signatures
in this spectral range. Measured hyperspectral attenuation signatures
of fine aerosols were comparable to calculated Mie scattering signatures,
suggesting that modal aerosol concentrations can be retrieved. A genetic
algorithm was adapted to estimate the aerosol modal concentrations
from its hyperspectral extinction signature. Retrievals of aerosol
concentrations from measured and synthetic hyperspectral signatures
indicated a robust algorithm, with an expected retrieval error of
0.2–22% for typical ambient concentrations along an urban-scale
open path. The retrieval accuracy was found to depend on the relative
aerosol modal concentrations, especially when there is a substantial
overlap between the modal spectral signatures
Monthly analysis of PM ratio characteristics and its relation to AOD
<p>Airborne particulate matter (PM) is derived from diverse sources—natural and anthropogenic. Climate change processes and remote sensing measurements are affected by the PM properties, which are often lumped into homogeneous size fractions that show spatiotemporal variation. Since different sources are attributed to different geographic locations and show specific spatial and temporal PM patterns, we explored the spatiotemporal characteristics of the PM<sub>2.5</sub>/PM<sub>10</sub> ratio in different areas. Furthermore, we examined the statistical relationships between AERONET aerosol optical depth (AOD) products, satellite-based AOD, and the PM ratio, as well as the specific PM size fractions. PM data from the northeastern United States, from San Joaquin Valley, CA, and from Italy, Israel, and France were analyzed, as well as the spatial and temporal co-measured AOD products obtained from the MultiAngle Implementation of Atmospheric Correction (MAIAC) algorithm. Our results suggest that when both the AERONET AOD and the AERONET fine-mode AOD are available, the AERONET AOD ratio can be a fair proxy for the ground PM ratio. Therefore, we recommend incorporating the fine-mode AERONET AOD in the calibration of MAIAC. Along with a relatively large variation in the observed PM ratio (especially in the northeastern United States), this shows the need to revisit MAIAC assumptions on aerosol microphysical properties, and perhaps their seasonal variability, which are used to generate the look-up tables and conduct aerosol retrievals. Our results call for further scrutiny of satellite-borne AOD, in particular its errors, limitations, and relation to the vertical aerosol profile and the particle size, shape, and composition distribution. This work is one step of the required analyses to gain better understanding of what the satellite-based AOD represents.</p> <p><i>Implications</i>: The analysis results recommend incorporating the fine-mode AERONET AOD in MAIAC calibration. Specifically, they indicate the need to revisit MAIAC regional aerosol microphysical model assumptions used to generate look-up tables (LUTs) and conduct retrievals. Furthermore, relatively large variations in measured PM ratio shows that adding seasonality in aerosol microphysics used in LUTs, which is currently static, could also help improve accuracy of MAIAC retrievals. These results call for further scrutiny of satellite-borne AOD for better understanding of its limitations and relation to the vertical aerosol profile and particle size, shape, and composition.</p