African dust over the Canaries. Long term variability of the summer Saharan dust export

Transcription

1 African dust over the Canaries Long term variability of the summer Saharan dust export Sergio Rodríguez Izaña Atmospheric Research Centre, AEMET, Tenerife 1

2 Long term aerosols: Total number concentration 26 Size distribution 1 nm SMPS 28 Size distribution.5 2 µm APS 27 Scattering total and back 3 l TSI neph 28 Absorption 1 l MAAP 27 Aethalometer 7 l 212 chemical composition 1987 Izaña, Tenerife Island 2 m.a.s.l., free troposphere (night) Teide peak, 3718 m.a.s.l.

3 aerosol chemical composition at Izaña (since 1987): dust (Al, Fe,...), SO 4 =, NO 3 -, NH 4 +, Na, and Cl - sample collection on filter cellulose University of Miami 3 m3/h Dust: ash method (normalized Al/dust 8%) SO =, 4 NO -, 3 NH +, 4 Cl - : ion chromatography Al, Na, Fe: INAA PM T : total particulate matter The two data sets were jointed for the firs time years aerosol chemistry in the free troposphere quartz microfibber filter samples collected at night free troposphere 22- up to the date 3 m3/h AEMET + CSIC Dust: elemental composition IPC- AES, ICP-MS (normalized Al/dust 8%) SO 4 =, NO 3 -,, Cl -: : ion chromatography NH 4+ : capillary electrophoresis, specific electrode OC, EC: TOR PM T : total particulate matter PM 1 : particulate matter diameter 1 µm PM 2.5 : particulate matter diameter 2.5 µm

4 PM T 91% 2.2% 1.2%.4% 1.9% 3.8%.2% PM 1 91% 2.2% 1.2%.4% 1.3% 3.4%.2% PM % 3.% 2.7% 1.% 1.1% 5.8%.4% 47.3 µg/m µg/m µg/m dust (Al, Fe, Ca, Ti..) none ammonium-sulfate ammonium-sulfate ammonium nitrate organic matter elemental carbon dust none ammonium-sulfate ammonium-sulfate ammonium nitrate organic matter elemental carbon dust none ammonium-sulfate ammonium-sulfate ammonium nitrate organic matter elemental carbon Al = 8% dust

5 number of dust events / month at Izaña: average A) summer Izaña B) winter Izaña Aerosol Index

6 We have focused in summer Why? Is the season when maximum dust emissions occurs in North Africa due to the activation of subtropical Saharan sources Processes that modulated inter-annual variability in dust export are still unknown Sahara summer Sahel winter scientific question Which are the large scale processes that influence on long term inter-annual variability in Saharan dust export in summer? Winter: North Atlantic Oscillation (Ginoux et al., 24) Sahel: Monsoon rains (Prospero and Lamb, 23)

7 Summer (August) mean dust T at Izaña from 1987 to 214 Saharan Air Layer dust T, µg/m Izaña Max: 133 μg/m Min: 17 μg/m MDFA: Major Dust Frequency Activity UV Absorbing Aerosol Index = sensitive to iron oxides in dust number days UV Absorbing Aerosol Index > 1 MDFA = total number of days in the month = fraction of summertime AI>1 Satellite (Earth Probe, Nimbus 7, Aura): Total Ozone Monitor Spectrometer ( ) Ozone Monitor Instrument (25-212)

8 Summer (August) mean dust T at Izaña from 1987 to 214 Saharan Air Layer dust T, µg/m Izaña large scale meteorology in North Africa 1.2. to climate variability 2. Size distribution: interannual variability

9 Summer (August) mean dust T at Izaña from 1987 to 214 Saharan Air Layer dust T, µg/m Izaña large scale meteorology in North Africa 1.2. to climate variability 2. Size distribution: interannual variability

10 large scale meteorology in North Africa Summer North African meteorological scenario Complex puzzle from the tropic to the Mediterranean: -Subtropical high pressures, 35ºN -Harmattan ( trade) winds 25-3 ºN -ITCZ, 2ºN -Saharan heat low, 19ºN -Tropical low monsoon, 7-12ºN rain band, 5-12ºN Inflow, 5-2ºN dust -2 km.a.s.l. Saharan Air Layer Izaña dust export off the coast of Africa 1-5 km.a.s.l. 85 hpa, 15 masl 7 hpa, 3 masl Tsamalis et al., 213. Atmos. Chem. Phys., 13, , 213

11 large scale meteorology in North Africa Summer North African meteorological scenario Complex puzzle from the tropic to the Mediterranean: -Subtropical high pressures, 35ºN H -Harmattan ( trade) winds 25-3 ºN -ITCZ, 2ºN -Saharan heat low, 19ºN -Tropical low monsoon, 7-12ºN rain band, 5-12ºN Inflow, 5-2ºN L North African Dipole Mean height of the 85hPa geopotential Aug

12 large scale meteorology in North Africa Summer North African meteorological scenario 7hPa geop. height 85hPa geop. height Izaña Morocco Bamako Mali Izaña North AFrican Dipole Intensity (NAFDI) 7 hpa: relevant level for dust export In principle, NAFDI is just a measure of the geostrophic component of the North African outflow but, we will see it is provides additional useful information on climate variability

13 large scale meteorology in North Africa dust T, µg/m Morocco Bamako Mali North AFrican Dipole Intensity 7 hpa: relevant level for dust export

14 large scale meteorology in North Africa dust T, µg/m r= Pearson correlation between NAFDI and the dust at Izaña = +.72 Variability in NAFDI is associated with dust export NAFD I Morocco Bamako Mali North AFrican Dipole Intensity 7 hpa: relevant level for dust export

15 large scale meteorology in North Africa 1987, 1996, 1997 and , -2.4, and , 2, 28 and , +.83, +1.1 and hpa geop. height 85 hpa geop. height

16 large scale meteorology in North Africa 1987, 1996, 1997 and , -2.4, and , 2, 28 and , +.83, +1.1 and hpa geop. height 7 hpa geop. height

17 large scale meteorology in North Africa 1987, 1996, 1997 and , -2.4, and , 2, 28 and , +.83, +1.1 and Subtropical Saharan Stripe-SSS: Central Algeria to Western Saharan, 24-3 N

18 SSS large scale meteorology in North Africa 12 8 r= correlation of NAFDI with zonal wind r=.69 r=.77

19 SSS large scale meteorology in North Africa Correlation coefficient between NAFDI and 12 8 r= zonal wind r=.69 r=.77 MDAF frequency precipitation rates back trajectories

20 SSS large scale meteorology in North Africa 12 8 r= correlation of NAFDI with zonal wind r=.69 r=.77 High NAFDI values are associated high wind speeds at the north of the ITCZ which prompts dust export at subtropical latitudes

21 large scale meteorology in North Africa 1987, 1996, 1997 and , -2.4, and , 2, 28 and , +.83, +1.1 and the monsoon rain band shift northward in high NAFDI summers

22 SSS large scale meteorology in North Africa 12 8 r= correlation of NAFDI with zonal wind r=.69 r=.77 precipitation rates r=.74 Wet Sahel Portion: portion of Sahel region (14-18 N to 17 W-22 E) that experienced a precipitation rate 3 mm/day

23 SSS large scale meteorology in North Africa 12 8 r=.72 r= correlation of NAFDI with zonal wind Dust Activity r=.77 precipitation rates r=.74 Wet Sahel Portion: portion of Sahel region (14-18 N to 17 W-22 E) that experienced a precipitation rate 3 mm/day

24 large scale meteorology in North Africa 12 8 Summary: 1. Variability in the summer dust export is associated with variability in the large scale meteorology in western North Africa as described in terms of NAFDI. 2. Increases in the values of NAFDI are associated with: -enhanced dust export to the subtropics (linked to winds at the north of the ITCZ) -less dust export to the tropic (linked to more rainfall in the tropic and southern Sahel) 3. Variability in the summer dust export in the last 28 years has been mainly controlled by winds (hyper arid Sahara vs Sahel hydrological sources)

25 Summer (August) mean dust T at Izaña from 1987 to 214 Saharan Air Layer dust T, µg/m Izaña large scale meteorology in North Africa 1.2. to climate variability 2. Size distribution: interannual variability

26 climate variability NAFD I

27 climate variability NAFD I

28 climate variability La Niña: strong trade winds (well defined regular meteorology in the subtropics and tropics) El Niño: weak trade winds (non regular meteorology in the subtropics and tropics) r(dust-izaña, NAFDI) =.72 r(dust-izaña, -MEI) =.59 MEI (NOAA): Multivariate ENSO (El Niño Southern Oscillation) Index =f(sea level pressure, zonal and meridional surface winds, sea surface T, surface air T and total cloudiness fraction of the sky over the tropical Pacific Ocean) El Niño periods tend to be associated with low NAFDI summers however, peak dust summers associated with MEI peaks but rather low NAFDI values (e.g. 22 and 21 )... La Niña periods tend to be associated with high NAFDI summers and vice versa, peak dust summers associated with NAFDI peaks but rather low MEI values (e.g. 212 ).

29 climate variability r(dust-izaña, NAFDI) =.72 r(dust-izaña, -MEI) =.59 r(dust-izaña, NAFDI+(-1) MEI) =.77 Dust export is sensitive to climate variability in the subtropic to tropics Further investigations tele-connection of MEI with winds in North Africa (?)

30 Summer (August) mean dust T at Izaña from 1987 to 214 Saharan Air Layer dust T, µg/m Izaña large scale meteorology in North Africa 1.2. to climate variability 2. Size distribution: interannual variability

31 Size distribution: interannual variability summer average

32 La Niña El Niño Saharan Air Layer Izaña Highlights: 1. Saharan dust export (August means): 17 μg/m 3 (1997) 133 μg/m 3 (212) 2. Dust export from the hyper arid Sahara region has been controlled (28y) by climate variability, particularly variability in the subtropics to tropics (NAFDI, MEI-ENSO) climate variability may modulate air quality downwind of the Sahara

33 PM1, µg/m In cities, people is expose to a cocktail of dust and pollutants: 1 PMx = pollutants + dust Local urban and regional pollution tend to increase during dust events gravimetria - suma de fuentes B) 35 Marino sea salt Mineral dust Barcos ships Refineria oil refinery Automóviles vehicle exhausts Tenerife, Canary Islands PM 1 = 171 µg/m 3 PM 1 = 1 µg/m 3 PM2.5, µg/m B) Percentil gravimetria - suma de fuentes Marino Mineral Barcos Refineria Vehiculos -temperature inversion at low levels: due to advections of warmer Saharan air -reaction of pollutants with dust (sulphate, nitrate, metals...) Percentil

34 PM 1 7 µg/m 3 (24-h)

35 La Niña El Niño Saharan Air Layer Izaña Highlights: 1. Saharan dust export (August means): 17 μg/m 3 (1997) 133 μg/m 3 (212) 2. Dust export from the hyper arid Sahara region has been controlled (28y) by climate variability, particularly variability in the subtropics and tropics (NAFDI, MEI-ENSO) climate variability may modulate air quality downwind of the Sahara 3. Implications for the Mediterranean (?) Subtropical Sahara dust sources, Mediterranean