Jul 9, 1995 - aerosol physical, optical, and chemical properties of aerosols .... Cliniatologies ot'retrospeclive air mass trajectories indicate ..... source regions: (a) Opcn North Atlantic; (b) North Atlantic with European influence; (c) North ...
JOURNAL OF GfiOPIIYSICAL RESEARCH, VOL. 105, NO. D l l , PAGES 14,677-14,700, RTNI:16, 2000
Aerosol physical and optical properties and their relationship to aerosol composition in the free troposphere at Izaiia, Tenerife, Canary Islands, during July 1995 H. Maring,' D. L. S a v o i e , l M. A. Izaguirre,l C. M c C o r m i c k , l R. Arimoto,2 J. M Prospero,l a n d C . Pilinis3
Abstract. Aerosol physical, optical, and chemical properties were measured at 2360 m above sea level over the Canary Islands during July 1995. Five aerosol size modes were observed. Nuclealiori aerosols 1 1 3 nm (geometric diameter) and a mode at 2 0 to 30 nm reflected local sources. A mode at 5 0 to 6 0 nm (likely from the upper atmosphere), another between 100 to 200 nm (pollutants), and mineral dust reflected distant sources. Greeri light scattering (adjusted to 1013 mbar and 0°C) ranged fro111below detection to > I 6 0 Mm-1 at relative humiditics m P
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MARING ET AL.: AEROSOL PHYSICAL, OPTICAL, AND CHEMICAL PROPERTIES
(Pallflex, Pall Gelman Laboratories, All11 Arbor, Michigan). Aerosol-laden quartz-fiber filters are crushed and pressed into polyethylene test tuhes, and the activities of 7Be and 2loPb are determined using an automated galnma ray spectroscopy system. This system consists of a high-pority germanii~ln well-type detector, a sample changer, and a multichannel analyzer [Grausrein and Turekinn, 19961. The uncertainties in 210Pb and 7Bc values (Table 1) are a combination of coullting error and uncertainty in the sample volume.
3.8. Chemical Sample Collection and Data Averaging Because of the die1 cycle of upslope winds during daylight hours and downslope flow at night, filter samples for chemical analysis of free tropospheric air were collected from 2000 to 0800UT on the following morning. These sa111pling periods are designated hereinafter by the dates in July of the beginning and end of the sampling period ( e g , 10 to 11, 20 to 21). In some cases we collected samples during the day when upslope winds carried material up from the boundary layer. These sampling periods ran from 0800 to 2UUUUS on llle same day and arc dssignaled in this paper by the date of thc sampling pcriod (c.g., 14 to 14, 20 to 20). In urdsr to compare the physcial and optical properties of tlic act.asols to thcil. chcniical propcrlics, we averaged aerosol light scattering, absorption, and sizc distributions ovcr thc bulk filter sanlpling periods. All chemical, radionuclide, particle, scattering, and absorption data have heen adjusted to I atmosphere and O0C.
4. Results and D i s c ~ ~ s s i o ~ i
(Table I). With the exception of 7Be and MSA, all chemical species and radionuclide activities were lower during the nondusty period than the dusty period. Since 7Bc is produced in the upper troposphere and lower stratosphere, it is not surprising that 7Be varies independently of those chemical species produced at the Earth's surface. Iluring the nondusty period, Sod= ranged from 0.2 to 1.2 g m-3. The air mass trajectories associated with thc two nights having the highest SO4= concentrations, 11 to 12 and 13 to 14, tracked over the most heavily populated and industrialized regions in North America (see Figure 2a). Trajectories associated with the remaining nighttime sampling periods of the nondusty period tracked only over the North Atlantic or over sparsely populated and undeveloped northern Canada (not shown). Even though the concentrations are low, it appears pollutants from North America are transported across the North Atlantic. Mineral dust concentrations increased, on average, 2 orders of magnitude from the nondusty to the dusty period. The coincident increase in the concentrations of SO4= and NO3with dust aerosol suggests the presence of pollutants fwln North Africa and probably Europe as well during the dusty period. Virtually no sea salt aerosol was present in thc frcc troposphere at Izaiia [Arimoto ct a/.,19951. Aerosol Na+ was correlated with dust during hoth the nonduqty and dusty periods (correlation coefficients: 0.86 and 0.88, respectively). Thus Kt and, for that matter, SO4= originated from sources other than sea salt and should be considered "non-sea salt." Consequently, in this paper, total aerosol Kt and SO4= are interchangeable with nss-K+ and nss-SO4=.
4.1. Event and Meteorological Description
4.3. Data Verificatinn
We started our sampling and measurements on the evening of July 3, 1995 and terminated sampling at 0800UT on July 29, 1995. Relrospective isentropic air irtass lrdjectories (J. T. Merrill, unpublished data, 1998) indicate that the air masses reaching the CAW station came from over the North Atlantic to the northwest ofthe Canary Islands from July 3 to 16, 1995 (Figure 2a). Concentrations of aerosol SO4= and dust were low, typically p l ~ c , c.\c, 11.: C . . . I < . l \ . (11. \:l..:.l.. l,', , I , , IL ? / , I , ??, .'%?!.?.,?\, . ,,: Quinn, P.K.', and D.S. C o h a n , Local closure during the First Acrusul Clreiili.lcri~aliul11E n p c ~ i l ~ i r ~(ACE tl 1): Azrusul mass cmcentration and scattering nnd backscartering coefficients. J. Guaphys. R P T ,1fl3, 16,575-16:596, 1998. Quinn, P.K., D.J. CoSSman, V.N. Kapustin, T.S. Bates, and D.S. Covert, Aerosol optical properties in the marine boundary layer during the First Aerosol Churucterizution Expel.iment (ACE 1) and the u n d e r l v i n ~cheniical and olivsical aerosol orooerties. J. Geophys. Res..'10~,16.547-16,563: 1498. Quinn, P.K.. S F . Marshall, T.S. Bates, D.S. Covert, and V.N. Kapustin, Comparison o f ~neasured and calculated aerosol properties relevant to tile dimct rodialive liircir~guC lmpospheric salfate aerosol on climate, .I Grophys. R r s , 100, 8977.8991,
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R. Arimuto, Carlsbad Environmental Monitoring and Research Center, New Mexico State UniLersity, Carlsbad, NM 88220. M. A. Izaguirre, H. Maring. C. McConnick, I . M. Prospero, and D. L. Savoie, Rosenstiel School of Marine and Atmospheric Science, University of ~Miami, FL 33149-1098 (hmarin,Ccdrslnas. miamieduj C. Pilinis, Environincntal Science Department, University of Aegean, Karadoni 17 - Mytilene, GK-8100 Levos, Greece.
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(Received Scplembzr 1, 1999; revised February 2, 2000; accepted February 8,2000.)
