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Vertical profiles of aerosol backscatter coefficient (black line) and pollen backscatter coefficient (red line). Gray-colored horizontal lines indicate the maximum height of the pollen plume on the basis of the pollen backscatter coefficient. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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For the first time, optical properties of biogenic pollen, i.e., backscatter coefficients and depolarization ratios at 532 nm were retrieved by lidar observations. The extinction coefficient was derived with the assumption of possible values of the extinction-to-backscatter (lidar) ratio. We investigate the effect of the pollen on the optical prope...
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Context 1
... again. This phenomenon repeated during the three days of lidar observations. We conclude that this pattern of the changing depolarization ratio from low to high values with height during daytime was induced by the increase of the concentration of non- spherical pollen particles in the atmosphere. Details can be found in Noh et al. (2012b). Fig. 3 shows hourly values of the total aerosol backscatter coefficient and the pollen-only backscatter coefficient calculated from Eqs. (3e5). The results are given for the time from 09:00 to 17:00 LT on 5, 6, and 7 May 2009. The pollen backscatter coefficient gradually increases with time and reaches its maximum around noon time. The ...
Context 2
... speed positively affect the concentration of pollen, i.e., lead to an increase of the pollen concentration. Alternatively, rainfall and humidity during pollination periods tend to decrease pollen concentrations. In the present study, when temperature and humidity met these pollen-releasing conditions, pollen concen- tration increased, as shown in Fig. 3, thereby inducing depolariza- tion scattering by the non-spherical shapes of pollen ( Noh et al., ...
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Citations
... Simultaneously, higher mixing layer height during afternoon hours enables more pollen grains released at the surface to be lifted above the lidar's minimum range of 90 m (see Table 2). This result also agrees with the previous findings (Noh et al., 2013a;Bohlmann et al., 2021), where the high δ from pollen is only observed in the boundary layer during daytime. ...
It has been demonstrated that HALO Photonics Doppler lidars (denoted HALO Doppler lidar hereafter) have the capability for retrieving the aerosol particle depolarization ratio at a wavelength of 1565 nm. For these lidars operating at such a long wavelength, the retrieval quality depends to a large degree on an accurate representation of the instrumental noise floor and the performance of the internal polarizer, whose stability has not yet been assessed for long-term operation. Here, we use 4 years of measurements at four sites in Finland to investigate the long-term performance of HALO Doppler lidars, focusing on aerosol particle depolarization ratio retrieval. The instrumental noise level, represented by noise-only signals in aerosol- and hydrometeor-free regions, shows stable performance for most instruments but clear differences between individual instruments. For all instruments, the polarizer bleed-through evaluated at liquid cloud base remains reasonably constant at approximately 1 % with a standard deviation of less than 1 %. We find these results to be sufficient for long-term aerosol particle depolarization ratio measurements and proceed to analyse the seasonal and diurnal cycles of the aerosol particle depolarization ratio in different environments in Finland, including in the Baltic Sea archipelago, a boreal forest and rural sub-arctic. To do so, we further develop the background correction method and construct an algorithm to distinguish aerosol particles from hydrometeors. The 4-year averaged aerosol particle depolarization ratio ranges from 0.07 in sub-arctic Sodankylä to 0.13 in the boreal forest in Hyytiälä. At all sites, the aerosol particle depolarization ratio is found to peak during spring and early summer, even exceeding 0.20 at the monthly-mean level, which we attribute to a substantial contribution from pollen. Overall, our observations support the long-term usage of HALO Doppler lidar depolarization ratio measurements, including detection of aerosols that may pose a safety risk for aviation.
... Simultaneously, higher mixing layer height during afternoon hours 430 enables more pollen grains released at the surface to be lifted above the lidar's minimum range. This result also agrees with the previous findings (Noh et al., 2013a;Bohlmann et al., 2021), where the high δaerosol from pollen is only observed in the boundary layer during daytime. ...
It has been demonstrated that Halo Doppler lidars have the capability for retrieving the aerosol particle linear depolarization ratio at a wavelength of 1565 nm. However, the retrieval depends on an accurate representation of the instrumental noise floor and the performance of the internal polarizer, whose stability have not been assessed in long-term operation. Here, we use four years of measurements at four sites in Finland to investigate the long-term performance of Halo Doppler lidars for aerosol particle depolarization ratio retrieval. The instrumental noise level, represented by noise-only signals in aerosol- and hydrometeor- free regions, shows stable performance for most instruments, but clear differences between individual instruments. For all instruments, the polarizer bleed-through evaluated at liquid cloud base remains reasonably constant at approximately 1 % with a standard deviation less than 1 %. We find these results sufficient for long-term aerosol particle linear depolarization ratio measurements and proceed to analyse the seasonal and diurnal cycles of the aerosol particle depolarization ratio in different environments in Finland including in the Baltic Sea archipelago, boreal forest and rural sub-arctic. To do so, we further develop the background correction method and construct an algorithm to distinguish aerosol particles from hydrometeors. The four-year averaged aerosol particle depolarization ratio ranges from 0.07 in sub-arctic Sodankylä to 0.13 in the boreal forest in Hyytiälä. At all sites, the aerosol particle depolarization ratio is found to peak during spring and early summer, even exceeding 0.20 at the monthly-mean level, which we attribute to a substantial contribution from pollen. Overall, our observations support the long-term usage of Halo Doppler lidar depolarization ratio including detection of aerosols that may pose a safety risk for aviation.
... The literature on lidar remote sensing of pollen however remains sparse. After pioneering work by Sassen et al. (2008) [14] and then Noh et al. (2013) [15], lidar remote sensing of pollen recently regained interest, possibly due to the emerging urgency of this topic. To detect and identify the involved pollen species, two main approaches have hence recently been developed: (i) the fluorescence technique, based on UV-light absorption by pollen [16], where pollens are identified through their fluorescence spectra [17], and (ii), the polarization technique, based on the nonspherical shape of pollen grains, where pollens are identified through their ability to depolarize laser light, quantified by the so-called particle depolarization ratio (PDR). ...
... The literature on lidar remote sensing of pollen however remains sparse. After pioneering work by Sassen et al. (2008) [14] and then Noh et al. (2013) [15], lidar remote sensing of pollen recently regained interest, possibly due to the emerging urgency of this topic. To detect and identify the involved pollen species, two main approaches have hence recently been developed: (i) the fluorescence technique, based on UV-light absorption by pollen [16], where pollens are identified through their fluorescence spectra [17], and (ii), the polarization technique, based on the nonspherical shape of pollen grains, where pollens are identified through their ability to depolarize laser light, quantified by the so-called particle depolarization ratio (PDR). ...
While pollen is expected to impact public human health and the Earth’s climate more and more in the coming decades, lidar remote sensing of pollen has become an important developing research field. To differentiate among the pollen taxa, a polarization lidar is an interesting tool since pollen exhibit non-spherical complex shapes. A key attribute is thus the lidar particle depolarization ratio (PDR) of pollen, which is however difficult to quantify as pollen are large and complex-shaped particles, far beyond the reach of light scattering numerical simulations. In this paper, a laboratory π-polarimeter is used to accurately evaluate the PDR of pure pollen, for the first time at the lidar exact backscattering angle of 180.0°. We hence reveal the lidar PDR of pure ragweed, ash, birch, pine, cypress and spruce pollens at 355 and 532 nm lidar wavelengths, as presented at the ELC 2021 conference. A striking result is the spectral dependence of the lidar PDR, highlighting the importance of dual-wavelength (or more) polarization lidars to identify pollen taxa. These spectral and polarimetric fingerprints of pure pollen, as they are accurate, can be used by the lidar community to invert multi-wavelength lidar polarization measurements involving pollen.
... Polarization management devices capable of fast and dynamic control over the SOP are highly desirable. For example, by analyzing the SOP of optical signal, light remote detection and ranging (LiDAR) systems can reveal the profiles and types of aerosol particles, which is important for monitoring air pollution and predicting climate change 11 . In this case, devices for SOP generation and measurement, with high-speed and high-accuracy, are crucial for improving the throughput and spatialtemporal resolutions of SOP LiDAR systems. ...
High-speed polarization management is highly desirable for many applications, such as remote sensing, telecommunication, and medical diagnosis. However, most of the approaches for polarization management rely on bulky optical components that are slow to respond, cumbersome to use, and sometimes with high drive voltages. Here, we overcome these limitations by harnessing photonic integrated circuits based on thin-film lithium niobate platform. We successfully realize a portfolio of thin-film lithium niobate devices for essential polarization management functionalities, including arbitrary polarization generation, fast polarization measurement, polarization scrambling, and automatic polarization control. The present devices feature ultra-fast control speeds, low drive voltages, low optical losses and compact footprints. Using these devices, we achieve high fidelity polarization generation with a polarization extinction ratio up to 41.9 dB and fast polarization scrambling with a scrambling rate up to 65 Mrad s−1, both of which are best results in integrated optics. We also demonstrate the endless polarization state tracking operation in our devices. The demonstrated devices unlock a drastically new level of performance and scales in polarization management devices, leading to a paradigm shift in polarization management. This work successfully demonstrates that thin-film lithium niobate platform can bring polarization management devices into a new phase of that higher speed, smaller size, and lower cost.
... Polarization management devices capable of fast and dynamic control over the SOP are highly desirable. For example, by analyzing the SOP of optical signal, light remote detection and ranging (LiDAR) systems can reveal the profiles and types of aerosol particles, which is important for monitoring air pollution and predicting climate change 11 . In this case, devices for SOP generation and measurement, with high-speed and high-accuracy, are crucial for improving the throughput and spatialtemporal resolutions of SOP LiDAR systems. ...
Based on thin-film lithium niobate platform, we experimentally demonstrate an endless automatic polarization controller which only requires a driving voltage range of 10 V, and achieves a polarization tracking speed of 10 Krad/s.
... An increasing interest has arisen to investigate the vertical distribution of pollen in the atmosphere. Studies show that lidar 40 measurements can detect the presence of pollen in the atmosphere, with a strong diurnal cycle on the pollen backscattering, and that the non-spherical pollen grains can generate strong depolarization of laser light (Bohlmann et al., 2019(Bohlmann et al., , 2021Noh et al., 2013aNoh et al., , 2013bSassen, 2008;Sicard et al., 2016). Therefore, it is possible to observe pollen in the atmosphere using the depolarization ratio in the absence of other depolarizing non-spherical particles (e.g. ...
Lidar observations were analysed to characterize atmospheric pollen at four EARLINET (European Aerosol Research Lidar Network) stations (Hohenpeißenberg, Germany; Kuopio, Finland, Leipzig, Germany; and Warsaw, Poland) during the ACTRIS-COVID-19 campaign in May 2020. The re-analysis lidar data products, after the centralized and automatic data processing with the Single Calculus Chain (SCC), were used in this study, focusing on particle backscatter coefficients at 355 nm and 532 nm, and particle linear depolarization ratios (PDRs) at 532 nm. A novel method for the characterization of the pure pollen depolarization ratio was presented, based on the non-linear least square regression fitting using lidar-derived backscatter-related Ångström exponents (BAEs) and PDRs. Under the assumption that the BAE between 355 and 532 nm should be zero (± 0.5) for pure pollen, the pollen depolarization ratios were estimated: for Kuopio and Warsaw stations, the pollen depolarization ratios at 532 nm were of 0.24 (0.19–0.28) during the birch dominant pollen periods; whereas for Hohenpeiβenberg and Leipzig stations, the pollen depolarization ratios of 0.21 (0.15–0.27) and 0.20 (0.15–0.25) were observed for periods of mixture of birch and grass pollen. The method was also applied for the aerosol classification, using two case examples from the campaign periods: the different pollen types (or pollen mixtures) were identified at Warsaw station, and dust and pollen were classified at Hohenpeißenberg station.
... They possess two air bladders which assist those pollen grains to be dispersed by wind despite their large size. The diameter of pine pollen grains on their longest axis is around 65-80 µm, while spruce pollen is considered very large for anemophilous pollen, with a diameter around 90-110 µm on the longest axis (Nilsson et al., 1977). The surface of the pollen corpus of spruce pollen is wrinkled and wavy (Grímsson and Zetter, 2011;Shen et al., 2020). ...
... Pollen release and distribution is heavily influenced by the ambient weather conditions. Higher temperature and wind speed positively affect the pollen concentration, while the relative humidity and pollen concentration are negative related ( Bartková-Ščevková, 2003;Noh et al., 2013). Under . ...
Lidar observations during the pollen season 2019 at the European Aerosol
Research Lidar Network (EARLINET) station in Kuopio, Finland, were analyzed
in order to optically characterize atmospheric pollen. Pollen concentration
and type information were obtained by a Hirst-type volumetric air sampler.
Previous studies showed the detectability of non-spherical pollen using
depolarization ratio measurements. We present lidar depolarization ratio
measurements at three wavelengths of atmospheric pollen in ambient
conditions. In addition to the depolarization ratio detected with the
multiwavelength Raman polarization lidar PollyXT at 355 and 532 nm,
depolarization measurements of a co-located Halo Doppler lidar at 1565 nm
were utilized. During a 4 d period of high birch (Betula) and spruce (Picea abies)
pollen concentrations, unusually high depolarization ratios were observed
within the boundary layer. Detected layers were investigated regarding the
share of spruce pollen to the total pollen number concentration. Daily mean
linear particle depolarization ratios of the pollen layers on the day with
the highest spruce pollen share are 0.10 ± 0.02, 0.38 ± 0.23 and
0.29 ± 0.10 at 355, 532 and 1565 nm, respectively, whereas on days
with lower spruce pollen share, depolarization ratios are lower with less
wavelength dependence. This spectral dependence of the depolarization ratios
could be indicative of big, non-spherical spruce pollen. The depolarization
ratio of pollen particles was investigated by applying a newly developed
method and assuming a backscatter-related Ångström exponent of zero.
Depolarization ratios of 0.44 and 0.16 at 532 and 355 nm for the birch and
spruce pollen mixture were determined.
... Des mesures de diffusion sur ces bioaérosols ont été réalisées en comparant la diffusion vers l'avant aux angles latéraux (Matsuda & Kawashima, 2018), et les figures de diffusion vers l'avant ont été étudiées spectralement (Holler et al., 2016). Des premières mesures de pollen atmosphériques ont été réalisées (Noh et al., 2013;Roy, 2010;Sassen, 2008;Sicard et al., 2016) mais se limitent au seul ratio de dépolarisation. Ainsi, l'étude des pollens par diffusion reste encore peu étudiée. ...
TITLE Bioaerosols light scattering (polarization-resolved): case study of ragweed pollen. RESUME Ce travail présente les résultats d'une publication récente dans JQSRT (Cholleton et al., 2020). Les pollens sont des bioaérosols atmosphériques ayant un fort impact sanitaire via les réactions allergiques qui agissent également sur le climat terrestre en contribuant à la nucléation et en intensifiant le flux radiatif descendant. Ces impacts sont amenés à s'intensifier sous l'effet du changement climatique. Parmi les bioaérosols, le pollen d'ambroisie est l'un des plus intéressants à étudier : principal allergène en France avec une prévalence de l'asthme deux fois supérieurs à d'autres pollens. Historiquement étudiés par microscopie, les pollens sont depuis une décennie étudiés par des méthodes optiques, telles que la diffusion optique. Les grains d'ambroisie ont une large taille (diamètre de 20 µm) et présentent une structure très complexe, avec des irrégularités de surface de l'ordre du micromètre. Ainsi, malgré une forme globalement sphérique, la diffusion par le pollen d'ambroisie ne suit à priori pas la théorie de Mie. Dans un contexte où les mesures en atmosphère restent rares, on se propose de quantifier en laboratoire la diffusion par le pollen d'ambroisie, et ceci à deux longueurs d'onde, afin d'en révéler la dépendance spectrale. ABSTRACT This work presents the results of a recent publication in JQSRT (Cholleton et al., 2020). Pollens are atmospheric bioaerosols with a strong health impact via allergic reactions that also act on the Earth's climate by contributing to nucleation and intensifying the downward radiative flux. These impacts are likely to intensify under the effect of climate change. Among all bioaerosols, ragweed pollen is one of the most interesting to study as being the main allergen in France with a prevalence of asthma twice as high as other pollens. Historically studied by microscopy, pollens have been studied for a decade by optical methods such as optical scattering. Ragweed grains have a large size (20 µm diameter) and exhibit a very complex structure, with surface irregularities of the order of a micrometre. Thus, despite a globally spherical shape, light scattering by ragweed pollen does not a priori follow the Mie theory. In a context where atmospheric measurements remain rather seldom, we here propose to quantify in the laboratory ragweed pollen light scattering, and this at two wavelengths, in order to reveal the spectral dependence of this phenomenon.
... Pollen release and distribution is heavily influenced by the ambient weather conditions. Higher temperature and wind speed positively affect the pollen concentration while the relative humidity and pollen concentration are negative related (Bartková-Ščevková, 2003;Noh et al., 2013). Under certain meteorological conditions, e.g. ...
Lidar observations during the pollen season 2019 at the European Aerosol Research Lidar Network (EARLINET) station in Kuopio, Finland were analyzed in order to optically characterize atmospheric pollen. Previous studies showed the detectability 15 of non-spherical pollen using depolarization ratio measurements. We present lidar depolarization ratio measurements at three wavelengths of atmospheric pollen in ambient conditions. In addition to the depolarization ratio detected with the multiwavelength Raman polarization lidar Polly XT at 355 and 532 nm, depolarization measurements of a co-located HALO Photonics Streamline Doppler lidar at 1565 nm were utilized. During a four days period of high birch (Betula) and spruce (Picea abies) pollen concentrations, unusually high depolarization ratios were observed within the boundary layer. Detected 20 layers were investigated regarding the share of spruce pollen to the total pollen number concentration. Daily mean particle depolarization ratios of the pollen layers on the day with the highest spruce pollen share are 0.10 ± 0.02, 0.38 ± 0.23 and 0.29 ± 0.10 at 355, 532 and 1565 nm, respectively. Whereas on days with lower spruce pollen share, depolarization ratios are lower with less wavelength dependence. This spectral dependence of the depolarization ratios could be indicative of big, non-spherical spruce pollen. The depolarization ratio of pollen particles was investigated by applying a newly developed method 25 and assuming a backscatter-related Ångström exponent of zero. Depolarization ratios of 0.44 and 0.16 at 532 and 355 nm for the birch and spruce pollen mixture were determined.
... At night, the high humidity, low temperature and low wind speed are the factors reducing the emissions (Sofiev et al., 2013a). Recent lidar observations confirm that tree pollen concentrations in the air at night are low (Noh et al., 2013). Therefore, it is reasonable to assume no pollen emission at night and a peak emission as a puff release in the morning as done here. ...
... Mandrioli et al. (1984) show vertical profile of pollen (their Figure 8) which corresponds to the decrease shown in our Fig. 5 (that is, pollen concentration is maximum near the surface and decreases to few grains/m 3 about two km of altitude above ground level). More recently, Noh et al. (2013) observed by lidar (light detection and ranging) that daily tree pollen is lifted to 1-2 km of altitude consistent with Fig. 5. Vertical dispersion of up to 1-2 km as shown in our simulations are also consistent with TDMLD of up to 1000 km as reported in Europe for Betula (Sofiev et al., 2006a,b). For example, a pollen particle at altitude of 1.5 km under a sedimentation velocity of 1.3 cm/s would be airborne for about 32 h. ...
Simulating allergenic tree pollen is important to protect sensitive population and to support bioaerosols monitoring effort. Using the regional air quality model GEM-MACH, a simulation was conducted adopting two new main hypotheses: 1) the use of vertical correlation concept to force the vertical dispersion (a method normally used in tracer data assimilation) and, 2) the use of a puff instead of a continuous pollen release. The simulation was compared with pollen observations in Montreal and with the corresponding statistical forecasts (issued daily by the Weather Network) at several locations in the province of Quebec and elsewhere. The comparison with the simulation was found satisfactory (outperform forecasts based on persistence or pollen calendar and is also superior to numerical simulation of tree pollen done elsewhere in North America). Simulation shows that, for the 2012 pollen season, the majority (88%) of the Betula pollen measured in Montreal originated from the Laurentides region. Another result of scientific importance obtained here is that Betula pollen episodes (observed or simulated birch pollen) in Montreal occur only when the average daily temperature is in the range of 10o to 18oC. This research is considered as a first step in forecasting bioaerosols in Canada within an air quality model.
