The detection and measurement of gas concentrations using the characteristic optical absorption of the gas species is important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. This study reviews the field, covering several individual gas detection techniques including non-dispersive infrared, spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy. We present the basis for each technique, recent developments in methods and performance limitations. The technology available to support this field, in terms of key components such as light sources and gas cells, has advanced rapidly in recent years and we discuss these new developments. Finally, we present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.

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Optical gas sensing: a review

Simulation results of global aerosol models have been assembled in the framework of the AeroCom intercomparison exercise. In this paper, we analyze the life cycles of dust, sea salt, sulfate, black carbon and particulate organic matter as simulated by sixteen global aerosol models. The differences among the results (model diversities) for sources and sinks, burdens, particle sizes, water uptakes, and spatial dispersals have been established. These diversities have large consequences for the calculated radiative forcing and the aerosol concentrations at the surface. Processes and parameters are identified which deserve further research. The AeroCom all-models-average emissions are dominated by the mass of sea salt (SS), followed by dust (DU), sulfate (SO 4 ), particulate organic matter (POM), and finally black carbon (BC). Interactive parameterizations of the emissions and contrasting particles sizes of SS and DU lead generally to higher diversities of these species, and for total aerosol. The lower diversity of the emissions of the fine aerosols, BC, POM, and SO 4 , is due to the use of similar emission inventories, and does therefore not necessarily indicate a better understanding of their sources. The diversity of SO 4 -sources is mainly caused by the disagreement on depositional loss of precursor gases and on chemical production. The diversities of the emissions are passed on to the burdens, but the latter are also strongly affected by the model-specific treatments of transport and aerosol processes. The burdens of dry masses decrease from largest to smallest: DU, SS, SO 4 , POM, and BC. The all-models-average residence time is shortest for SS with about half a day, followed by SO 4 and DU with four days, and POM and BC with six and seven days, respectively. The wet deposition rate is controlled by the solubility and increases from DU, BC, POM to SO 4 and SS. It is the dominant sink for SO 4 , BC, and POM, and contributes about one third to the total removal of SS and DU species. For SS and DU we find high diversities for the removal rate coefficients and deposition pathways. Models do neither agree on the split between wet and dry deposition, nor on that between sedimentation and other dry deposition processes. We diagnose an extremely high diversity for the uptake of ambient water vapor that influences the particle size and thus the sink rate coefficients. Furthermore, we find little agreement among the model results for the partitioning of wet removal into scavenging by convective and stratiform rain. Large differences exist for aerosol dispersal both in the vertical and in the horizontal direction. In some models, a minimum of total aerosol concentration is simulated at the surface. Aerosol dispersal is most pronounced for SO 4 and BC and lowest for SS. Diversities are higher for meridional than for vertical dispersal, they are similar for the individual species and highest for SS and DU. For these two components we do not find a correlation between vertical and meridional aerosol dispersal. In addition the degree of dispersals of SS and DU is not related to their residence times. SO 4 , BC, and POM, however, show increased meridional dispersal in models with larger vertical dispersal, and dispersal is larger for longer simulated residence times.

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Analysis and quantification of the diversities of aerosol life cycles within AeroCom

[1] The atmospheric chemistry of volatile organic compounds (VOCs) in urban areas results in the formation of ‘photochemical smog’, including secondary organic aerosol (SOA). State-of-the-art SOA models parameterize the results of simulation chamber experiments that bracket the conditions found in the polluted urban atmosphere. Here we show that in the real urban atmosphere reactive anthropogenic VOCs (AVOCs) produce much larger amounts of SOA than these models predict, even shortly after sunrise. Contrary to current belief, a significant fraction of the excess SOA is formed from first-generation AVOC oxidation products. Global models deem AVOCs a very minor contributor to SOA compared to biogenic VOCs (BVOCs). If our results are extrapolated to other urban areas, AVOCs could be responsible for additional 3–25 Tg yr−1 SOA production globally, and cause up to −0.1 W m−2 additional top-of-the-atmosphere radiative cooling.

Secondary Organic Aerosol Formation from Anthropogenic Air Pollution: Rapid and Higher than Expected

Ozone holds a certain fascination in atmospheric science. It is ubiquitous in the atmosphere, central to tropospheric oxidation chemistry, yet harmful to human and ecosystem health as well as being an important greenhouse gas. It is not emitted into the atmosphere but is a by-product of the very oxidation chemistry it largely initiates. Much effort is focussed on the reduction of surface levels of ozone owing to its health impacts but recent efforts to achieve reductions in exposure at a country scale have proved difficult to achieve due to increases in background ozone at the zonal hemispheric scale. There is also a growing realisation that the role of ozone as a short-lived climate pollutant could be important in integrated air quality climate-change mitigation. This review examines current understanding of the processes regulating tropospheric ozone at global to local scales from both measurements and models. It takes the view that knowledge across the scales is important for dealing with air quality and climate change in a synergistic manner.

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Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer

https://escholarship.org/content/qt8mf445sh/qt8mf445sh.pdf?t=nu02or

Atmospheric composition change – global and regional air quality

Abstract. The purpose of this study is to investigate the ability of the Sentinel-5P
TROPOspheric Monitoring Instrument (TROPOMI) to derive accurate geometrical
features of lofted aerosol layers, selecting the Mediterranean
Basin as the study area. Comparisons with ground-based correlative measurements constitute a
key component in the validation of passive and active satellite aerosol
products. For this purpose, we use ground-based observations from quality-controlled lidar stations reporting to the European Aerosol Research Lidar
Network (EARLINET). An optimal methodology for validation purposes has been
developed and applied using the EARLINET optical profiles and TROPOMI
aerosol products, aiming at the in-depth evaluation of the TROPOMI aerosol
layer height (ALH) product for the period 2018 to 2022 over the
Mediterranean Basin. Seven EARLINET stations were chosen, taking into
consideration their proximity to the sea, which provided 63 coincident
aerosol cases for the satellite retrievals. In the following, we present the
first validation results for the TROPOMI/S5P ALH using the optimized
EARLINET lidar products employing the automated validation chain designed
for this purpose. The quantitative validation at pixels over the selected
EARLINET stations illustrates that the TROPOMI ALH product is consistent with
the EARLINET lidar products, with a high correlation coefficient R=0.82
(R=0.51) and a mean bias of -0.51±0.77 km and -2.27±1.17 km
over ocean and land, respectively. Overall, it appears that aerosol layer
altitudes retrieved from TROPOMI are systematically lower than altitudes
from the lidar retrievals. High-albedo scenes, as well as low-aerosol-load
scenes, are the most challenging for the TROPOMI retrieval algorithm, and
these results testify to the need to further investigate the underlying
cause. This work provides a clear indication that the TROPOMI ALH product
can under certain conditions achieve the required threshold accuracy and precision
requirements of 1 km, especially when only ocean pixels are included in the
comparison analysis. Furthermore, we describe and analyse three case studies
in detail, one dust and two smoke episodes, in order to illustrate the
strengths and limitations of the TROPOMI ALH product and demonstrate the
presented validation methodology. The present analysis provides important
additions to the existing validation studies that have been performed so far
for the TROPOMI S5P ALH product, which were based only on
satellite-to-satellite comparisons.


/pdf/validation-of-the-tropomi-s5p-aerosol-layer-height-using-3r00qwdt.pdf

Validation of the TROPOMI/S5P aerosol layer height using EARLINET lidars

In this paper we present an intercomparison between ground based lidar, radiosonde and satellite atmospheric water vapor measurements. Comparisons expressed in terms of water vapor profiles, obtained by Raman lidar and simultaneous ballonborne radiosonde, are reported and discussed. The deviation between the two profiles is smaller than 10 percent up to an altitude of 5 km. Furthermore, the intercomparison between lidar and radiosonde data and between lidar and satellite data is performed also in terms of water vapor columnar content. The agreement between lidar and radiosonde columnar content is better than 4 percent. Water vapor contour map are showed in order to demonstrate the high spatial and temporal variability of water vapor in the lower atmosphere. Difficulties in comparing lidar and satellite water vapor columnar contents associated to H2O spatial and temporal variability are discussed in the paper.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Atmospheric water vapor measurements using ground- and satellite-based instrumentation and radiosonde

/pdf/front-matter-volume-7479-23vunap9cp.pdf

Front Matter: Volume 7479

Two tailored configurations of the Robust Satellite Technique (RST) multi-temporal approach, for airborne volcanic ash and desert dust detection, have been tested in the framework of the European Natural Airborne Disaster Information and Coordination System for Aviation (EUNADICS-AV) project. The two algorithms, running on Spinning Enhanced Visible Infra-Red Imager (SEVIRI) data, were previously assessed over wide areas by comparison with independent satellite-based aerosol products. In this study, we present results of a first validation analysis of the above mentioned satellite-based ash/dust products using independent, ground-based observations coming from the European Aerosol Research Lidar Network (EARLINET). The aim is to assess the capabilities of RST-based ash/dust products in providing useful information even at local scale and to verify their applicability as a “trigger” to timely activate EARLINET measurements during airborne hazards. The intense Saharan dust event of May 18–23 2008—which affected both the Mediterranean Basin and Continental Europe—and the strong explosive eruptions of Eyjafjallajokull (Iceland) volcano of April–May 2010, were analyzed as test cases. Our results show that both RST-based algorithms were capable of providing reliable information about the investigated phenomena at specific sites of interest, successfully detecting airborne ash/dust in different geographic regions using both nighttime and daytime SEVIRI data. However, the validation analysis also demonstrates that ash/dust layers remain undetected by satellite in the presence of overlying meteorological clouds and when they are tenuous (i.e., with an integrated backscatter coefficient less than ~0.001 sr−1 and with aerosol backscatter coefficient less than ~1 × 10−6 m−1sr−1). This preliminary analysis confirms that the continuity of satellite-based observations can be used to timely “trigger” ground-based LIDAR measurements in case of airborne hazard events. Finally, this work confirms that advanced satellite-based detection schemes may provide a relevant contribution to the monitoring of ash/dust phenomena and that the synergistic use of (satellite-based) large scale, continuous and timely records with (ground-based) accurate and quantitative measurements may represent an added value, especially in operational scenarios.

Gelsomina Pappalardo

Papers

Validation of the TROPOMI/S5P aerosol layer height using EARLINET lidars

Atmospheric water vapor measurements using ground- and satellite-based instrumentation and radiosonde

Front Matter: Volume 7479

Validation of Ash/Dust Detections from SEVIRI Data Using ACTRIS/EARLINET Ground-Based LIDAR Measurements

Aerosol classification using EARLINET measurements for an intensive observational period