Validation of TROPOMI Surface UV Radiation Product

The TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor (S5P) satellite was launched on 13 October 2017 to provide the atmospheric composition for atmosphere and climate research. The S5P is a sun-synchronous polar-orbiting satellite providing global daily coverage. The TROPOMI swath is 2600 km wide, and the ground resolution for most data products is 7.2x3.5 km2 (5.6x3.5 km2 since 6 August 2019) at nadir. The Finnish Meteorological Institute (FMI) is responsible for the development and processing of the TROPOMI Surface Ultraviolet (UV) Radiation Product which includes 36 UV parameters in total. Ground-based data from 25 sites located in arctic, subarctic, temperate, equatorial and antarctic areas were used for validation of TROPOMI overpass irradiance at 305, 310, 324 and 380 nm, overpass erythemally weighted dose rate / UV index and erythemally weighted daily dose for the period from 1 January 2018 to 31 August 2019. The validation results showed that for most sites 60–80% of TROPOMI data was within ±20% from ground-based data for snow free surface conditions. The median relative differences to ground-based measurements of TROPOMI snow free surface daily doses were within ±10% and ±5% at two thirds and at half of the sites, respectively. At several sites more than 90% of clear sky TROPOMI data were within ±20% from ground-based measurements. Generally median relative differences between TROPOMI data and ground-based measurements were a little biased towards negative values, but at high latitudes where nonhomogeneous topography and albedo/snow conditions occurred, the negative bias was exceptionally high, from -30% to -65%. Positive biases of 10–15% were also found for mountainous sites due to challenging topography. The TROPOMI Surface UV Radiation Product includes quality flags to detect increased uncertainties in the data due to heterogeneous surface albedo and rough terrain which can be used to filter the data retrieved under challenging conditions

Caractérisation d'épisodes de pollution particulaire observés in situ sur la plateforme d'observations de Lille

National audienc

Rayonnement UV solaire en France métropolitaine et à La Réunion : érythème et synthèse de la vitamine D

International audienceSolar UV radiation induces beneficial and detrimental effects on human health. Health agencies recommend avoiding sun exposure when UV radiation is maximum: between 2 h before and after solar noon in summer. A reduction in UV exposure being susceptible to reduce vitamin D synthesis, it is useful to estimate and compare exposure durations leading to erythema and to sufficient vitamin D production. These duration times were calculated using UV radiation measurements from spectroradiometers operating continuously at 3 French sites. One observes that exposure duration requested for vitamin D synthesis is generally shorter than that inducing erythema. Moreover, the time periods where limited solar exposure is recommended should be extended, especially at low latitude locations: in summer at least between 3 h before and after solar noon at mainland sites and, at La Réunion, between 4 h before and after solar noon. In spring and autumn, prudence is also needed.Le rayonnement UV solaire a des effets bénéfiques et délétères pour la santé humaine. Les agences de santé recommandent d'éviter l'exposition lorsque le rayonnement UV est maximum : entre 2 heures avant et après midi solaire en été. Une réduction de l'exposition UV pouvant entraîner une diminution de la synthèse de vitamine D, il est utile d'estimer et de comparer les durées d'exposition induisant un érythème ou une production suffisante de vitamine D. Ces durées ont été établies à partir de mesures du rayonnement UV obtenues à l'aide de spectroradiomètres opérant en continu sur trois sites français. On constate que la durée d'exposition nécessaire à la synthèse de vitamine D est généralement inférieure à celle induisant l'érythème. De plus, les périodes durant lesquelles une exposition limitée est recommandée devraient être étendues, spécialement aux basses latitudes : en été au moins entre 3 heures avant et après le midi solaire en métropole et, à La Réunion, entre 4 heures avant et après le midi solaire. Au printemps et en automne, il faut également être prudent

New Particle Formation observed in the close vicinity of a French megalopolis

International audienc

New Particle Formation observed in the close vicinity of a French megalopolis

International audienc

Measurement report: Atmospheric new particle formation at a peri-urban site in Lille, northern France

International audienceFormation of ultrafine particles (UFPs) in the urban atmosphere is expected to be less favored than in the rural atmosphere due to the high existing particle surface area acting as a sink for newly formed particles. Despite large condensation sink (CS) values, previous comparative studies between rural and urban sites reported higher frequency of new particle formation (NPF) events over urban sites in comparison to background sites as well as higher particle formation and growth rates attributed to the higher concentration of condensable species. The present study aims at a better understanding the environmental factors favoring, or disfavoring, atmospheric NPF over Lille, a large city in the north of France, and to analyze their impact on particle number concentration using a 4-year long-term dataset. The results highlight a strong seasonal variation of NPF occurrences with a maximum frequency observed during spring (27 events) and summer (53 events). It was found that high temperature (T > 295 K), low relative humidity (RH < 45 %), and high solar radiation are ideal to observe NPF events over Lille. Relatively high CS values (i.e., ∼ 2 × 10 −2 s −1) are reported during event days suggesting that high CS does not inhibit the occurrence of NPF over the ATmospheric Observations in LiLLE (ATOLL) station. Moreover, the particle growth rate was positively correlated with temperatures most probably due to higher emission of precursors. Finally, the nucleation strength factor (NSF) was calculated to highlight the impact of those NPF events on particle number concentrations. NSF reached a maximum of four in summer, evidencing a huge contribution of NPF events to particle number concentration at this time of the year

Validation of the TROPOspheric Monitoring Instrument (TROPOMI) surface UV radiation product

The TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor (S5P) satellite was launched on 13 October 2017 to provide the atmospheric composition for atmosphere and climate research. The S5P is a Sun-synchronous polar-orbiting satellite providing global daily coverage. The TROPOMI swath is 2600 km wide, and the ground resolution for most data products is 7.2×3.5 km2 (5.6×3.5 km2 since 6 August 2019) at nadir. The Finnish Meteorological Institute (FMI) is responsible for the development of the TROPOMI UV algorithm and the processing of the TROPOMI surface ultraviolet (UV) radiation product which includes 36 UV parameters in total. Ground-based data from 25 sites located in arctic, subarctic, temperate, equatorial and Antarctic areas were used for validation of the TROPOMI overpass irradiance at 305, 310, 324 and 380 nm, overpass erythemally weighted dose rate/UV index, and erythemally weighted daily dose for the period from 1 January 2018 to 31 August 2019. The validation results showed that for most sites 60 %–80 % of TROPOMI data was within ±20 % of ground-based data for snow-free surface conditions. The median relative differences to ground-based measurements of TROPOMI snow-free surface daily doses were within ±10 % and ±5 % at two-thirds and at half of the sites, respectively. At several sites more than 90 % of cloud-free TROPOMI data was within ±20 % of ground-based measurements. Generally median relative differences between TROPOMI data and ground-based measurements were a little biased towards negative values (i.e. satellite data < ground-based measurement), but at high latitudes where non-homogeneous topography and albedo or snow conditions occurred, the negative bias was exceptionally high: from −30 % to −65 %. Positive biases of 10 %–15 % were also found for mountainous sites due to challenging topography. The TROPOMI surface UV radiation product includes quality flags to detect increased uncertainties in the data due to heterogeneous surface albedo and rough terrain, which can be used to filter the data retrieved under challenging conditions