scholarly journals Large and seasonally varying biospheric CO2 fluxes in the Los Angeles megacity revealed by atmospheric radiocarbon

2020 ◽  
Vol 117 (43) ◽  
pp. 26681-26687 ◽  
Author(s):  
John B. Miller ◽  
Scott J. Lehman ◽  
Kristal R. Verhulst ◽  
Charles E. Miller ◽  
Riley M. Duren ◽  
...  
Keyword(s):  
Los Angeles ◽  
Urban Areas ◽  
Fossil Fuel ◽  
Carbon Sink ◽  
Mediterranean Ecosystems ◽  
Urban Vegetation ◽  
Human Metabolism ◽  
Water Usage ◽  
Reliable Methods ◽  
Net Carbon Sink

Measurements of Δ14C and CO2 can cleanly separate biogenic and fossil contributions to CO2 enhancements above background. Our measurements of these tracers in air around Los Angeles in 2015 reveal high values of fossil CO2 and a significant and seasonally varying contribution of CO2 from the urban biosphere. The biogenic CO2 is composed of sources such as biofuel combustion and human metabolism and an urban biospheric component likely originating from urban vegetation, including turf and trees. The urban biospheric component is a source in winter and a sink in summer, with an estimated amplitude of 4.3 parts per million (ppm), equivalent to 33% of the observed annual mean fossil fuel contribution of 13 ppm. While the timing of the net carbon sink is out of phase with wintertime rainfall and the sink seasonality of Southern California Mediterranean ecosystems (which show maximum uptake in spring), it is in phase with the seasonal cycle of urban water usage, suggesting that irrigated urban vegetation drives the biospheric signal we observe. Although 2015 was very dry, the biospheric seasonality we observe is similar to the 2006–2015 mean derived from an independent Δ14C record in the Los Angeles area, indicating that 2015 biospheric exchange was not highly anomalous. The presence of a large and seasonally varying biospheric signal even in the relatively dry climate of Los Angeles implies that atmospheric estimates of fossil fuel–CO2 emissions in other, potentially wetter, urban areas will be biased in the absence of reliable methods to separate fossil and biogenic CO2.

scholarly journals A Simplified Framework for High-Resolution Urban Vegetation Classification with Optical Imagery in the Los Angeles Megacity

2020 ◽  
Vol 12 (15) ◽  
pp. 2399 ◽  
Author(s):  
Red Willow Coleman ◽  
Natasha Stavros ◽  
Vineet Yadav ◽  
Nicholas Parazoo
Keyword(s):  
Los Angeles ◽  
Land Cover ◽  
Spatial Resolution ◽  
Urban Areas ◽  
High Spatial Resolution ◽  
Water Cycle ◽  
Bare Soil ◽  
Urban Vegetation ◽  
Optical Imagery ◽  
Sentinel 2

High spatial resolution maps of Los Angeles, California are needed to capture the heterogeneity of urban land cover while spanning the regional domain used in carbon and water cycle models. We present a simplified framework for developing a high spatial resolution map of urban vegetation cover in the Southern California Air Basin (SoCAB) with publicly available satellite imagery. This method uses Sentinel-2 (10–60 × 10–60 m) and National Agriculture Imagery Program (NAIP) (0.6 × 0.6 m) optical imagery to classify urban and non-urban areas of impervious surface, tree, grass, shrub, bare soil/non-photosynthetic vegetation, and water. Our approach was designed for Los Angeles, a geographically complex megacity characterized by diverse Mediterranean land cover and a mix of high-rise buildings and topographic features that produce strong shadow effects. We show that a combined NAIP and Sentinel-2 classification reduces misclassified shadow pixels and resolves spatially heterogeneous vegetation gradients across urban and non-urban regions in SoCAB at 0.6–10 m resolution with 85% overall accuracy and 88% weighted overall accuracy. Results from this study will enable the long-term monitoring of land cover change associated with urbanization and quantification of biospheric contributions to carbon and water cycling in cities.

scholarly journals Findings From the Understanding Patterns of Healthy Aging Among Men Who Have Sex With Men Project

2020 ◽  
Vol 4 (Supplement_1) ◽  
pp. 823-824
Author(s):  
Mark Brennan-Ing ◽  
Michael Plankey ◽  
Deborah Gustafson
Keyword(s):  
Los Angeles ◽  
Urban Areas ◽  
Healthy Aging ◽  
Research Policy ◽  
Disease Risk ◽  
Well Being ◽  
Hiv Status ◽  
Gay Community ◽  
Regulatory Strategies ◽  
Sex With Men

Abstract In 1984, the Multicenter AIDS Cohort Study (MACS) was started to identify factors in the HIV epidemic related to disease risk and treatment progression among gay, bisexual, and other men who have sex with men (MSM) in four urban areas in the US: Baltimore, MD/Washington, D.C.; Chicago, IL; Pittsburgh, PA, and Los Angeles, CA. MACS participants complete biannual study visits involving HIV testing, biometric screenings, and psychosocial data collection. In 2015 a MACS sub-study, the Understanding Patterns of Healthy Aging among MSM Project (HAMSM), was started to better understand resiliencies promoting well-being among MSM age 40 and older, including those with HIV. HAMSM has helped us to understand aging trajectories among MSM, and provides a unique combination of physiological and psychosocial data that can inform efforts to support MSM in healthy aging. This symposium will present emerging findings from the HAMSM study. Our first paper examines the relationships between psychological connection to the gay community (PSOC) and developmental regulatory strategies associated with health behaviors and more positive self-appraisals. The second paper examines how PSOC is related to HIV risk reduction behaviors, and if there are differences in such behaviors based on HIV status. Our third paper considers how self-perceptions of aging (age discrepancy, aging satisfaction) are related to frailty and frailty transitions, and if these relationships differ by HIV status. The final paper examines the relationship of social support to frailty among MSM by HIV status. Implications of these findings for research, policy, and programs targeting MSM will be discussed.

Toward CO2 and CH4 measurements by ground-based observations of surface-scattered sunlight

2021 ◽  
Author(s):  
Benedikt Hemmer ◽  
Christin Proß ◽  
Stanley P. Sander ◽  
Thomas J. Pongetti ◽  
Zhao-Cheng Zeng ◽  
...  
Keyword(s):  
Los Angeles ◽  
Urban Areas ◽  
Near Infrared ◽  
Chem Phys ◽  
Retrieval Algorithm ◽  
Los Angeles Basin ◽  
Satellite Measurements ◽  
Precise Knowledge ◽  
Extended Sources

<div> <div>Precise knowledge of sources and sinks in the carbon cycle is desired to understand its sensitivity to climate change and to account and verify man-made emissions. In this context, extended sources like urban areas play an important role. While in-situ measurements of carbon dioxide (CO<sub>2</sub>) and methane (CH<sub>4</sub>) are highly accurate but localized, satellites measure column-integrated concentrations over an extended footprint. The CLARS-FTS [1, 2] stationed at the Mt. Wilson observatory looking downward into the Los Angeles basin has pioneered an innovative measurement technique that fills the sensitivity gap between in-situ and satellite measurements. The technique enables mapping the urban greenhouse gas concentration fields by collecting spectra of ground scattered sunlight and scanning through the region.</div> <div> </div> <div>Here, we report on progress developing a portable setup for a CLARS-FTS-like measurement geometry. The instrument is based on the EM27/SUN FTS with a modified pointing technique and a more sensitive detector. The retrieval algorithm is based on the RemoTeC software, previously employed for solar backscatter satellite measurements. We discuss first steps in terms of instrument performance and retrieval exercises. For the latter, we have carried out simulations on how the neglect of scattering by the retrieval affects the retrieved boundary layer concentrations of CO<sub>2</sub> and CH<sub>4</sub> for an ensemble of hypothetical scenes with variable complexity in aeorsol loadings and viewing geometry. We also report on a test to apply RemoTeC to a small set of CLARS-FTS spectra collected throughout the Los Angeles basin.</div> <div> </div> <div><em>References</em></div> <div>[1] Fu, D. et al., 2014: Near-infrared remote sensing of Los Angeles trace gas distributions from a mountaintop site, Atmos. Meas. Tech., 7, 713–729, https://doi.org/10.5194/amt-7-713-2014</div> [2] Wong, K. W. et al., 2015: Mapping CH4 : CO2 ratios in Los Angeles with CLARS-FTS from Mount Wilson, California, Atmos. Chem. Phys., 15, 241–252, https://doi.org/10.5194/acp-15-241-2015</div>

scholarly journals Household accessibility to heat refuges: Residential air conditioning, public cooled space, and walkability

2016 ◽  
Vol 44 (6) ◽  
pp. 1036-1055 ◽  
Author(s):  
Andrew M Fraser ◽  
Mikhail V Chester ◽  
David Eisenman ◽  
David M Hondula ◽  
Stephanie S Pincetl ◽  
...  
Keyword(s):  
Los Angeles ◽  
Public Space ◽  
Urban Areas ◽  
Air Conditioning ◽  
Regional Climate ◽  
Heat Exposure ◽  
Household Level ◽  
Private And Public ◽  
Residential Air Conditioning ◽  
Walking Speeds

Access to air conditioned space is critical for protecting urban populations from the adverse effects of heat exposure. Yet there remains fairly limited knowledge of the penetration of private (home air conditioning) and distribution of public (cooling centers and commercial space) cooled space across cities. Furthermore, the deployment of government-sponsored cooling centers is likely to be inadequately informed with respect to the location of existing cooling resources (residential air conditioning and air conditioned public space), raising questions of the equitability of access to heat refuges. We explore the distribution of private and public cooling resources and access inequities at the household level in two major US urban areas: Los Angeles County, California and Maricopa County, Arizona (whose county seat is Phoenix). We evaluate the presence of in-home air conditioning and develop a walking-based accessibility measure to air conditioned public space using a combined cumulative opportunities-gravity approach. We find significant variations in the distribution of residential air conditioning across both regions which are largely attributable to building age and inter/intra-regional climate differences. There are also regional disparities in walkable access to public cooled space. At average walking speeds, we find that official cooling centers are only accessible to a small fraction of households (3% in Los Angeles, 2% in Maricopa) while a significantly higher number of households (80% in Los Angeles, 39% in Maricopa) have access to at least one other type of public cooling resource such as a library or commercial establishment. Aggregated to a neighborhood level, we find that there are areas within each region where access to cooled space (either public or private) is limited which may increase heat-related health risks.

scholarly journals Inter-community variability in total particle number concentrations in the eastern Los Angeles air basin

2010 ◽  
Vol 10 (23) ◽  
pp. 11385-11399 ◽  
Author(s):  
N. Hudda ◽  
K. Cheung ◽  
K. F. Moore ◽  
C. Sioutas
Keyword(s):  
Los Angeles ◽  
Spatial Variability ◽  
Spatial Variation ◽  
Urban Areas ◽  
Particle Number ◽  
Meteorological Conditions ◽  
Monitoring Station ◽  
Size Distributions ◽  
Central Monitoring ◽  
Seasonal And Diurnal Variations

Abstract. Ultrafine Particles (UFP) can display sharp gradients in their number concentrations in urban environment due to their transient nature and rapid atmospheric processing. The ability of using air pollution data generated at a central monitoring station to assess exposure relies on our understanding of the spatial variability of a specific pollutant associated with a region. High spatial variation in the concentrations of air pollutants has been reported at scales of 10s of km for areas affected by primary emissions. Spatial variability in particle number concentrations (PNC) and size distributions needs to be investigated, as the representativeness of a monitoring station in a region is premised on the assumption of homogeneity in both of these metrics. This study was conducted at six sites, one in downtown Los Angeles and five located about 40–115 km downwind in the receptor areas of Los Angeles air basin. PNC and size distribution were measured using Condensation Particle Counters (CPC) and Scanning Mobility Particle Sizer (SMPS). The seasonal and diurnal variations of PNC implied that PNC might vary significantly with meteorological conditions, even though the general patterns at the sites may remain generally similar across the year due to consistency of sources around them. Regionally transported particulate matter (PM) from upwind urban areas of Los Angeles lowered spatial variation by acting as a "homogenizing" factor during favorable meteorological conditions. Spatial variability also increased during hours of the day during which the effects of local sources predominate. The spatial variability associated with PNC (quantified using Coefficients of Divergence, CODs), averaged about 0.3, which was generally lower than that based on specific size ranges. Results showed an inverse relationship of COD with particles size, with fairly uniform values in the particle range which is associated with regional transport. Our results suggest that spatial variability, even in the receptor regions of Los Angeles Basin, should be assessed for both PNC and size distributions, and should be interpreted in context of seasonal and diurnal influences, and suitably factored if values for exposure are ascertained using a central monitoring station.

scholarly journals What can be learned about carbon cycle climate feedbacks from the CO<sub>2</sub> airborne fraction?

2010 ◽  
Vol 10 (16) ◽  
pp. 7739-7751 ◽  
Author(s):  
M. Gloor ◽  
J. L. Sarmiento ◽  
N. Gruber
Keyword(s):  
Land Use ◽  
Fossil Fuel ◽  
Carbon Sink ◽  
Volcanic Eruptions ◽  
Atmospheric Co2 ◽  
Anthropogenic Emissions ◽  
Term Trend ◽  
Decadal Scale ◽  
Long Term Trend

Abstract. The ratio of CO2 accumulating in the atmosphere to the CO2 flux into the atmosphere due to human activity, the airborne fraction AF, is central to predict changes in earth's surface temperature due to greenhouse gas induced warming. This ratio has remained remarkably constant in the past five decades, but recent studies have reported an apparent increasing trend and interpreted it as an indication for a decrease in the efficiency of the combined sinks by the ocean and terrestrial biosphere. We investigate here whether this interpretation is correct by analyzing the processes that control long-term trends and decadal-scale variations in the AF. To this end, we use simplified linear models for describing the time evolution of an atmospheric CO2 perturbation. We find firstly that the spin-up time of the system for the AF to converge to a constant value is on the order of 200–300 years and differs depending on whether exponentially increasing fossil fuel emissions only or the sum of fossil fuel and land use emissions are used. We find secondly that the primary control on the decadal time-scale variations of the AF is variations in the relative growth rate of the total anthropogenic CO2 emissions. Changes in sink efficiencies tend to leave a smaller imprint. Therefore, before interpreting trends in the AF as an indication of weakening carbon sink efficiency, it is necessary to account for trends and variations in AF stemming from anthropogenic emissions and other extrinsic forcing events, such as volcanic eruptions. Using atmospheric CO2 data and emission estimates for the period 1959 through 2006, and our simple predictive models for the AF, we find that likely omissions in the reported emissions from land use change and extrinsic forcing events are sufficient to explain the observed long-term trend in AF. Therefore, claims for a decreasing long-term trend in the carbon sink efficiency over the last few decades are currently not supported by atmospheric CO2 data and anthropogenic emissions estimates.

scholarly journals Automatic Extraction of Grasses and Individual Trees in Urban Areas Based on Airborne Hyperspectral and LiDAR Data

2020 ◽  
Vol 12 (17) ◽  
pp. 2725
Author(s):  
Qixia Man ◽  
Pinliang Dong ◽  
Xinming Yang ◽  
Quanyuan Wu ◽  
Rongqing Han
Keyword(s):  
Urban Areas ◽  
Three Dimensional ◽  
Hyperspectral Data ◽  
Classification Method ◽  
Urban Vegetation ◽  
Individual Tree ◽  
Cloud Data ◽  
Random Forest Classification ◽  
The Individual ◽  
Individual Trees

Urban vegetation extraction is very important for urban biodiversity assessment and protection. However, due to the diversity of vegetation types and vertical structure, it is still challenging to extract vertical information of urban vegetation accurately with single remotely sensed data. Airborne light detection and ranging (LiDAR) can provide elevation information with high-precision, whereas hyperspectral data can provide abundant spectral information on ground objects. The complementary advantages of LiDAR and hyperspectral data could extract urban vegetation much more accurately. Therefore, a three-dimensional (3D) vegetation extraction workflow is proposed to extract urban grasses and trees at individual tree level in urban areas using airborne LiDAR and hyperspectral data. The specific steps are as follows: (1) airborne hyperspectral and LiDAR data were processed to extract spectral and elevation parameters, (2) random forest classification method and object-based classification method were used to extract the two-dimensional distribution map of urban vegetation, (3) individual tree segmentation was conducted on a canopy height model (CHM) and point cloud data separately to obtain three-dimensional characteristics of urban trees, and (4) the spatial distribution of urban vegetation and the individual tree delineation were assessed by validation samples and manual delineation results. The results showed that (1) both the random forest classification method and object-based classification method could extract urban vegetation accurately, with accuracies above 99%; (2) the watershed segmentation method based on the CHM could extract individual trees correctly, except for the small trees and the large tree groups; and (3) the individual tree segmentation based on point cloud data could delineate individual trees in three-dimensional space, which is much better than CHM segmentation as it can preserve the understory trees. All the results suggest that two- and three-dimensional urban vegetation extraction could play a significant role in spatial layout optimization and scientific management of urban vegetation.

scholarly journals Differential Column Measurements Using Compact Solar-Tracking Spectrometers

2016 ◽  
Author(s):  
Jia Chen ◽  
Camille Viatte ◽  
Jacob K. Hedelius ◽  
Taylor Jones ◽  
Jonathan E. Franklin ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Los Angeles ◽  
Urban Areas ◽  
Integration Time ◽  
Small Scale ◽  
Los Angeles Basin ◽  
Solar Tracking ◽  
Regional Sources ◽  
New Applications ◽  
Atmospheric Phenomena

Abstract. We demonstrate the use of compact solar-tracking Fourier transform spectrometers (Bruker EM27/SUN) for differential measurements of the column-averaged dry-air mole fractions of CH4 and CO2 within urban areas. Using Allan variance analysis, we show that the differential column measurement has a precision of 0.1 ‰ for XCO2 and XCH4 using an optimum integration time of 10 min, which corresponds to standard deviations of 0.04 ppm, and 0.2 ppb, respectively. The sensor system is very stable over time and after relocation across the continent. We report tests of the differential column measurement, and its sensitivity to emission sources, by measuring the downwind minus upwind column gradient ΔXCH4 across dairy farms in the Chino California area and using the data to verify emissions reported in the literature. Spatial column gradient ratios ΔXCH4/ΔXCO2 were observed across Pasadena within the Los Angeles basin, indicating values consistent with regional emission ratios from the literature. Our precise, rapid measurements allow us to determine significant short-term variations (5–10 minutes) of ΔXCO2 and ΔXCH4, and to show that they represent atmospheric phenomena. Overall, this study helps establish a range of new applications for compact solar-viewing Fourier transform spectrometers. By accurately measuring the small differences in integrated column amounts across local and regional sources, we directly observe the mass loading of the atmosphere due to the influence of emissions in the intervening locale. The inference of the source strength is much more direct than inversion modeling using only surface concentrations, and less subject to errors associated with small-scale transport phenomena.

scholarly journals Characteristics of PM<sub>2.5</sub> speciation in representative megacities and across China

2011 ◽  
Vol 11 (1) ◽  
pp. 1025-1051 ◽  
Author(s):  
F. Yang ◽  
J. Tan ◽  
Q. Zhao ◽  
Z. Du ◽  
K. He ◽  
...  
Keyword(s):  
Los Angeles ◽  
Atmospheric Pollution ◽  
Urban Areas ◽  
Fine Particles ◽  
Chemical Species ◽  
Northern Region ◽  
Eastern Region ◽  
Mobile Source ◽  
Combustion Source ◽  
Geographical Regions

Abstract. Based on PM2.5 chemical database from literature and our observations, chemical species and reconstructed speciation of PM2.5 in several representative Chinese megacities and across China were compared to draw insights into the characteristics of PM2.5 speciation. PM2.5 mass and speciation varied substantially over geographical regions in China. Near six-fold variations in average PM2.5 concentrations (34.0–193.4 μg m−3) across China were found with high PM2.5 levels (>100 μg m−3) appearing along northern region and in western urban areas. At both urban and rural sites in eastern region, sum of sulfate, nitrate, and ammonia (SNA) typically constituted 40–57% of PM2.5 mass, indicative of the regional characteristics of fine particulate pollution and more intensive "complex atmospheric pollution" compared to western region. Particulate organic matter (POM) had constant and significant contribution to PM2.5 mass. POM plus SNA accounted for 62–90% of PM2.5 mass at most of the sites. PM2.5 speciation in China was also characterized by high content of mineral dust. In four representative megacities (i.e. Beijing, Chongqing, Shanghai, and Guangzhou) with substantially higher levels of all the species except that NO3−, NH4+, and EC in PM2.5 than those in Los Angeles, distinct differences in nitrate and sulfate levels and their mass ratio [NO3−]/[SO42−] imply that mobile source is likely more important than stationary (coal combustion) source in Guangzhou whereas in Chongqing the situation is contrary. The observed intra-city variations in PM2.5 mass and speciation indicate that local emissions and regional transportation both contributed significantly to high fine particles levels in Beijing, while local contribution likely played a predominant role in Chongqing. During the ten-year period from 1999 through 2008 in urban Beijing, both SNA and [NO3−]/[SO42−] exhibited steadily increasing trends, implying that the characteristic of "complex atmospheric pollution" and the contribution from mobile sources were both being enhanced.

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