Precipitable water vapour content from ESR/SKYNET sun–sky radiometers: validation against GNSS/GPS and AERONET  over three different sites in Europe

Campanelli, Monica; Mascitelli, Alessandra; Sanò, Paolo; Diémoz, Henri; Estellés, V.; Federico, Stefano; Iannarelli, Anna Maria; Fratarcangeli, Francesca; Mazzoni, Augusto; Realini, Eugenio; Crespi, Mattia; Bock, Olivier; Martínez‐Lozano, J. A.; Dietrich, Stefano

doi:10.5194/amt-11-81-2018

Cited by 36 publications

(40 citation statements)

References 32 publications

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“…Indeed, an SH increase occurs on the first day of the sequence (starting from minimum values of ∼8 g kg −1 in the morning to about 11 g kg −1 in the evening) as soon as the wind starts blowing and high values (> 13 g kg −1 ) endure for the rest of the week, likely indicating that the dry air, typical of the more mixed mountain PBL (Henne et al, 2005;Mélin and Zibordi, 2005), is replaced by more stagnating, and humidified, air masses characteristic of hot summer days in the Po Valley (Bucci et al, 2018). This scenario is compatible with recent findings by Campanelli et al (2018), who performed water vapour measurements with the POM-02 at Aosta-Saint Christophe and found that moist air masses are mainly coming from the east.…”

Section: Meteorological Variables and Back-trajectoriessupporting

confidence: 90%

Transport of Po Valley aerosol pollution to the northwestern Alps. Part 1: phenomenology

Diémoz¹,

Barnaba²,

Magri³

et al. 2018

Preprint

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Abstract. Mountainous regions are often considered pristine environments, however they can be affected by pollutants emitted in more populated and industrialised areas, transported by regional winds. Based on experimental evidence, further supported by modelling tools, we demonstrate and quantify here the impact of air masses transported from the Po Valley, a European atmospheric pollution hotspot, to the northwestern Alps. This is achieved through a detailed investigation of the phenomenology of near-range (few hundreds km), trans-regional transport, exploiting synergies of multi-sensor observations mainly focussed on particulate matter. The explored dataset includes vertically-resolved data from atmospheric profiling techniques (Automated LiDAR-Ceilometers, ALC), vertically-integrated aerosol properties from ground (sun photometer) and space, and in situ measurements (PM10 and PM2.5, relevant chemical analyses, and aerosol size distribution). During the frequent advection episodes from the Po basin, all the physical quantities observed by the instrumental setup are found to significantly increase: the scattering ratio from ALC reaches values > 30, AOD triplicates, surface PM10 reaches concentrations > 100 µg/m3 even in rural areas, secondary inorganic compounds such as nitrate, ammonium and sulfate increase up to 28 %, 8 % and 17 % of the total PM10 mass, respectively. Results also indicate that the advected aerosol is smaller in size and less light-absorbing compared to the aerosol type locally-emitted in the northwestern Italian Alps, and hygroscopic. In this work, the phenomenon is exemplified through detailed analysis and discussion of three case studies, selected for their clarity and relevance within the wider dataset, the latter being fully exploited in a companion paper quantifying the impact of this phenomenology over the long-term (Diémoz et al., 2018). For the three case studies investigated, a high-resolution numerical weather prediction model (COSMO) and a lagrangian tool (LAGRANTO) are employed to understand the meteorological mechanisms favouring the transport and to demonstrate the Po Valley origin of the air masses. In addition, a chemical transport model (FARM) is used to further support the observations and to partition the contributions of local and non-local sources. Results show that the simulations are not able to adequately reproduce the measurements (with modelled PM10 concentrations 4–5 times lower than the ones retrieved from the ALC, and maxima anticipated by 6–7 hours), likely owing to deficiencies in the emission inventory and particle water uptake not fully taken into account. The advected aerosol is shown to remarkably degrade the air quality of the Alpine region, with potential negative effects on human health, climate and ecosystems, as well as on the touristic development of the investigated area. The findings of the present study could also help design mitigation strategies at the trans–regional scale in the Po basin, and suggest an observations-based approach to evaluate the outcome of their implementation.

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Section: Meteorological Variables and Back-trajectoriessupporting

confidence: 90%

Transport of Po Valley aerosol pollution to the northwestern Alps. Part 1: phenomenology

Diémoz¹,

Barnaba²,

Magri³

et al. 2018

Preprint

Self Cite

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“…This kind of secondary inorganic aerosol was indeed found in high concentrations in the Po basin by previous studies (e.g. Putaud et al, 2002Putaud et al, , 2010Carbone et al, 2010;Larsen et al, 2012;Saarikoski et al, 2012;Gilardoni et al, 2014;Curci et al, 2015). Here we further tested on a longer dataset whether the sum of the nitrate-and sulfate-rich factors (i.e.…”

Section: Chemical Species Within the Advected Aerosol Layerssupporting

confidence: 79%

Transport of Po Valley aerosol pollution to the northwestern Alps – Part 2: Long-term impact on air quality

et al. 2019

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Abstract. This work evaluates the impact of trans-regional aerosol transport from the Po basin on particulate matter levels (PM10) and physico-chemical characteristics in the northwestern Alps. To this purpose, we exploited a multi-sensor, multi-platform database over a 3-year period (2015–2017) accompanied by a series of numerical simulations. The experimental setup included operational (24/7) vertically resolved aerosol profiles by an automated lidar ceilometer (ALC), vertically integrated aerosol properties by a Sun/sky photometer, and surface measurements of aerosol mass concentration, size distribution and chemical composition. This experimental set of observations was then complemented by modelling tools, including numerical weather prediction (NWP), trajectory statistical (TSM) and chemical transport (CTM) models, plus positive matrix factorisation (PMF) on both the PM10 chemical speciation analyses and particle size distributions. In a first companion study, we showed and discussed through detailed case studies the 4-D phenomenology of recurrent episodes of aerosol transport from the polluted Po basin to the northwestern Italian Alps. Here we draw more general and statistically significant conclusions on the frequency of occurrence of this phenomenon, and on the quantitative impact of this regular, wind-driven, aerosol-rich “atmospheric tide” on PM10 air-quality levels in this alpine environment. Based on an original ALC-derived classification, we found that an advected aerosol layer is observed at the receptor site (Aosta) in 93 % of days characterized by easterly winds (i.e. from the Po basin) and that the longer the time spent by air masses over the Po plain the higher this probability. Frequency of these advected aerosol layers was found to be rather stable over the seasons with about 50 % of the days affected. Duration of these advection events ranges from few hours up to several days, while aerosol layer thickness ranges from 500 up to 4000 m. Our results confirm this phenomenon to be related to non-local emissions, to act at the regional scale and to largely impact both surface levels and column-integrated aerosol properties. In Aosta, PM10 and aerosol optical depth (AOD) values increase respectively up to factors of 3.5 and 4 in dates under the Po Valley influence. Pollution transport events were also shown to modify the mean chemical composition and typical size of particles in the target region. In fact, increase in secondary species, and mainly nitrate- and sulfate-rich components, were found to be effective proxies of the advections, with the transported aerosol responsible for at least 25 % of the PM10 measured in the urban site of Aosta, and adding up to over 50 µg m−3 during specific episodes, thus exceeding alone the EU established daily limit. From a modelling point of view, our CTM simulations performed over a full year showed that the model is able to reproduce the phenomenon, but markedly underestimates its impact on PM10 levels. As a sensitivity test, we employed the ALC-derived identification of aerosol advections to re-weight the emissions from outside the boundaries of the regional domain in order to match the observed PM10 field. This simplified exercise indicated that an increase in such “external” emissions by a factor of 4 in the model is needed to halve the model PM10 maximum deviations and to significantly reduce the PM10 normalised mean bias forecasts error (from −35 % to 5 %).

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“…The slope of curvature (M) represents the average characterization of the solar aureole shape across the scattering angle 3.2-6.0 • range in which a large magnitude signifies the potential presence of large particles as curvature increases with increasing scattering angle across the forward scattering peak. The Micro-Pulse Lidar Network (MPLNET) is a global network of lidars monitoring the vertical distribution of aerosols and clouds (Welton et al, 2000;Welton and Campbell, 2002;Campbell et al, 2002). To determine the thresholds for these Sun photometer solar aureole curvature parameters for different surface types and aerosol environments, the MPLNET lidar cloud identification database was used at eight collocated AERONET sites as shown in Table 3.…”

Section: Novel Cirrus Removal Methods Utilizing Solar Aureole Curvaturementioning

confidence: 99%

Advancements in the Aerosol Robotic Network (AERONET) Version 3 database – automated near-real-time quality control algorithm with improved cloud screening for Sun photometer aerosol optical depth (AOD) measurements

et al. 2019

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Abstract. The Aerosol Robotic Network (AERONET) has provided highly accurate, ground-truth measurements of the aerosol optical depth (AOD) using Cimel Electronique Sun–sky radiometers for more than 25 years. In Version 2 (V2) of the AERONET database, the near-real-time AOD was semiautomatically quality controlled utilizing mainly cloud-screening methodology, while additional AOD data contaminated by clouds or affected by instrument anomalies were removed manually before attaining quality-assured status (Level 2.0). The large growth in the number of AERONET sites over the past 25 years resulted in significant burden to the manual quality control of millions of measurements in a consistent manner. The AERONET Version 3 (V3) algorithm provides fully automatic cloud screening and instrument anomaly quality controls. All of these new algorithm updates apply to near-real-time data as well as post-field-deployment processed data, and AERONET reprocessed the database in 2018. A full algorithm redevelopment provided the opportunity to improve data inputs and corrections such as unique filter-specific temperature characterizations for all visible and near-infrared wavelengths, updated gaseous and water vapor absorption coefficients, and ancillary data sets. The Level 2.0 AOD quality-assured data set is now available within a month after post-field calibration, reducing the lag time from up to several months. Near-real-time estimated uncertainty is determined using data qualified as V3 Level 2.0 AOD and considering the difference between the AOD computed with the pre-field calibration and AOD computed with pre-field and post-field calibration. This assessment provides a near-real-time uncertainty estimate for which average differences of AOD suggest a +0.02 bias and one sigma uncertainty of 0.02, spectrally, but the bias and uncertainty can be significantly larger for specific instrument deployments. Long-term monthly averages analyzed for the entire V3 and V2 databases produced average differences (V3–V2) of +0.002 with a ±0.02 SD (standard deviation), yet monthly averages calculated using time-matched observations in both databases were analyzed to compute an average difference of −0.002 with a ±0.004 SD. The high statistical agreement in multiyear monthly averaged AOD validates the advanced automatic data quality control algorithms and suggests that migrating research to the V3 database will corroborate most V2 research conclusions and likely lead to more accurate results in some cases.

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Precipitable water vapour content from ESR/SKYNET sun–sky radiometers: validation against GNSS/GPS and AERONET over three different sites in Europe

Cited by 36 publications

References 32 publications

Transport of Po Valley aerosol pollution to the northwestern Alps. Part 1: phenomenology

Transport of Po Valley aerosol pollution to the northwestern Alps. Part 1: phenomenology

Transport of Po Valley aerosol pollution to the northwestern Alps – Part 2: Long-term impact on air quality

Advancements in the Aerosol Robotic Network (AERONET) Version 3 database – automated near-real-time quality control algorithm with improved cloud screening for Sun photometer aerosol optical depth (AOD) measurements

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