CHARACTERIZATION OF AEROSOL HYGROSCOPIC GROWTH
OVER MADRID THROUGH REMOTE SENSING TECHNIQUES
A. J. Fernández, F. Molero, M. Becerril-Valle, E. Alonso-Blanco, M. Barreiro, L. Núñez, P. Salvador, M. Palacios, F. J. Gómez, E. Díaz, E. Coz, A. Hernanz, B. Artíñano and M. Pujadas
Department of Environment. Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Avda Complutense, 40. Madrid, 28040. (Spain)
Contact information: [email protected]
Experimental site:
Introduction:
Barajas Airport
CIEMAT
and
AEMET
The lidar station is located at Madrid
(40.45ºN, 3.73ºW, 663 m asl) inside
the CIEMAT facilities. This station is
part of the European Aerosol Research
LIdar NETwork (EARLINET ).
One of the major uncertainties in radiative forcing estimates is the effect of aerosols
on the formation, characteristics and distribution of clouds (AR5-IPCC, 2013).
Hygroscopicity plays a crucial role as increases in relative humidity (RH) modify
aerosol optical properties, for instance: an enlargement in size, scattering or a
Radiosoundings are launched from
Barajas Airport, located at 13.5 km
east from the lidar station (see Fig. 1).
diminishment of refractive index. Since the RH increases with height, it is important
to observe and characterize the vertical distribution of aerosol properties at the
same time as RH in order to provide useful information for radiative forcing
The AEMET’s sun-sky photometer is
located 500 m far away from the
CIEMAT site
modeling.
Ground based lidars have become powerful tools as they can procure such
Figure 1. CIEMAT Lidar station, AEMET sunphotometer and radiosounding launching locations.
The Multiwavelength (3+2+1) Raman lidar system is based on:
information with high resolution both in time and vertical dimension. In this work,
• Pulsed Nd:Yag laser, (Spectra Physics model Quanta-Ray Lab 130-70), Repetition rate: 30 Hz, Energy/pulse: 214 mJ
at 1064 nm, 145 mJ at 532 nm and 138 mJ at 355 nm.
we present two events of aerosol hygroscopic growth observed at ambient
conditions in Madrid through remote sensing techniques: the multiwavelenth
• Newtonian telescope (Orion-Optics Dobson) with a 300 mm diameter primary reflective mirror and a 1200 mm
focal length.
Raman lidar station deployed at CIEMAT (Research Center for Energy,
• Detection line: 6 channels separated by dichroic mirrors and interferential filters. 3 elastic channels (1064, 532 and
355 nm) and 3 Raman channels (387 and 607 nm (nitrogen) and 407nm (water vapor)). Photomultiplier tubes (PMT)
for 355, 387, 407, 532 and 607 m channels and a Si-avalanche photodiode module (APD) for 1064 nm channel.
Acquisition data system: A transient recorder model licel TR-40-80
Environment and Technology) and ancillary instrumentation such as the sun-sky
photometer (CIMEL Electronique 318A spectral radiometer) installed at the AEMET
(Spanish Meteorological Agency) facilities.
.
Methodology and results:
The backscatter (β) and extinction (α) coefficients profiles were obtained by inverting (Klett, 1981) the time intervals shadowed in figure 3A & 4A. Then the β-Ångström exponent (ȧβ) is derived according to its
definition: ȧβ = -dln β(λ)/dln (λ) (fig. 3B&4B). The vertical distribution of the water vapour mixing ratio is estimated from the two Raman channel ratio (H2O(v):407 nm and N2:387 nm) (Whiteman et al., 1992).
Hence, relative humidity profiles are obtained from pressure and temperature profiles (radiosondes) and from water vapour mixing ratio profiles using the expressions described by Mattis et al. (2002). The
characterization of aerosol hygroscopic growth processes has been done through the calculation of the enhancement factor f(RH) from the general form of the Hänel equation (1976) particularized here for the
lidar-retrieved backscatter coefficient (532nm), fb (RH), (fig. 3C&4C). A well mixed boundary layer is required to avoid a misleading conclusion regarding hygroscopicity. The virtual potential temperature
(radiosondes) and water vapour profiles (lidar) are used as tracers since they maintain constant inside of a well mixed atmosphere. Aerosol size distributions are obtained from sun-sky photometer observations
so as to study, if possible, the effect of aerosol hygroscopic growth on such distributions (Dubovik and King, 2000) (fig. 3D&4D). Additionally, backward trajectories are obtained from the HSYPLIT model in
order to analyze the origin of air masses and therefore to determine possible aerosol composition (fig.3E&4E).
.
1st case study, June 3rd, 2013:
LIDAR-CIEMAT, Madrid, Range Corrected Signal @ 532 nm
7
120000
x107
(C)
(B)
(A)
(D)
(E)
6
100000
5
Height agl (m)
8000
4
6000
3
4000
2
2000
1
0
20:00
0
20:30
21:00
21:30
Time (UTC)
Figure 3. (A).- Colour-coded plot of the Range Corrected Signal at 532nm . Lidar products (20:15-20:25h UTC): (B).-Vertical profiles of relative humidity and β-Ångström exponent (532/355nm), (C).- The enhancement factor particularized for β (532 nm).
(D).- Aerosol size distributions (three modes) are provided by the sun-sky photometer. (E).- Backward trajectories at 1800, 2500 and 3300m agl which point out an Atlantic air masses origin.
2nd case study, June 20th, 2013:
LIDAR-CIEMAT, Madrid, Range Corrected Signal @ 532 nm
x107
4,5
5000
2
4
(A)
4000
3,5
(B)
(C)
(D)
(E)
Height agl (m)
3
3000
2,5
3
1
2
2
2000
1,5
1
1
1000
0,5
0
23:00
23:20
23:40
00:00
0
3
Time (UTC)
Figure 4. (A).- Colour-coded plot of the Range Corrected Signal at 532 nm. Lidar products (23:15-23:30h UTC): (B).- Vertical profiles of relative humidity and β-Ångström exponent (532/355nm), (C).- Evolution of β(532 nm) as a function of relative
humidity throughout the atmospheric levels: 1470, 2220 and 2580 m agl (points 1, 2 and 3 respectively). (D).- Aerosol size distributions (three modes) are obtained by the sun-sky photometer. (E).- Backward trajectories at 1500, 2000 and 3000 m agl
which point out an Atlantic air masses origin.
Discussion and conclusions
Two aerosol hygroscopic growth processes at the top of the atmospheric mixing layer in Madrid have been detected. They are characterised by a decrease of the β-Ångström exponent as the relative humidity increases. Their
full identification has been based on analysis the enhancement factor for β (532 nm) throughout the atmospheric vertical column. A plausible hysteresis in β (532) evolution has been observed when relative humidity
augments and diminishes as altitude increases. The stepply pattern identified at a relative humidity of 70% might be linked to deliquescence processes. This hypothesis is supported by the marine origin of air masses present
at the altitude where hygroscopic behaviour took place. It can be observed in figures 3E&4E where backward trajectories calculated by the HYSPLIT model are represented. Marine aerosols are comprised of crystaline
substances which in turn are very likely to exhibit deliquescence. Moreover, AERONET retrievals present aerosol size distributions which are composed of three modes during aerosol hygroscopic events.. This fact is
remarkable given that most AERONET retrievals usually show a bimodal aerosol size distribution at least in Madrid. Further research is required in order to better characterize these phenomena.
References
1.- Dubovik and King (2000). Jour. Geophys. Res, 105, 20673-20696
2.- Hänel, G. (1976). Advances in Geophysics, 19, 73 – 188
3.- Holben et al. (1998). Rem . Sens. of Environ. 66, 1 –16
4.- IPCC. (2013). Summary for Policymakers in Climate Change
5.- Klett, J. D. (1981). Appl. Opt., 20, 211-220
6.-.Mattis, I. et al. (2002). Appl. Opt. 41(30), 6451 – 6462
7.- Pappalardo, G. et al. (2014). Atmos. Meas. Tech.., 7, 2389 – 2409
8.- Whiteman, D. N. et al. (1992). Appl. Opt. 31, 3068 – 3082
ACKNOWLEDGMENTS
The research leading to these results has received funding from ACTRIS-2-H-2020 (grant agreement n° 654109) and also from the MICINN (Spanish Ministry of Science and Innovation) under
project CGL2014-52877-R. We thank AERONET and Juan Ramón Moreta González for their effort in establishing and maintaining the Madrid site. The authors gratefully acknowledge the NOAA
Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and/or READY website (http://www.arl.noaa.gov/ready.php) used in this publication.
3th ACTRIS-2 General and MTR Meeting,
February 2017,
Granada, Spain