Jim Smith

Scientist II
TIIMES - ACD
BEACHON - UTLS

Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: FL0 - 3100
Telephone: 303-497-1468
Email: jimsmith@ucar.edu
Home Page | Group webpage

Project Summary:

I am a scientist and the head of the Ultrafine Aerosols Research Group in the Atmospheric Chemistry Division (ACD) at NCAR.  Ultrafine aerosols are particles with diameters smaller than 100 nm, and are important because they can perturb our climate through the modification of clouds and precipitation.  My research activities address three questions that are of fundamental importance to atmospheric chemistry and climate:

• How can we characterize the physico-chemical properties of the smallest particles in the atmosphere?

• What are the impacts of biogenic emissions on aerosol formation, and how do these impacts vary with climate change and land use practices?

• How do newly formed aerosols grow in the atmosphere to become important participants in chemistry/climate?

 

Activities of the Ultrafine Aerosols (UA) Research Group

The UA group conducts measurements to understand how particles form in the atmosphere and how they grow to become important participants in atmospheric chemistry and climate.   Ultrafine aerosols are particles with diameters smaller than 100 nm.  They can be formed in the atmosphere over spatial scales of hundreds of kilometers by a process known as new particle formation.  Measurements by the UA group and its collaborators performed in atmospheric environments as diverse as Mexico City (Figure 1a) and the boreal forests in central Finland (Figure 1b) confirm that new particle formation occurs frequently, and often is the fundamental process that controls particle number (Figure 1c).  As a demonstration of the latter, a recent modeling study of the southern ocean atmosphere has concluded that new particle formation add as much as 8 times more particles compared to anthropogenic primary particle sources [1].

The research activities of the UA group address three questions that are of fundamental importance to atmospheric chemistry and climate:

1. How can we characterize the physico-chemical properties of the smallest particles in the atmosphere?

2. What are the impacts of biogenic emissions on aerosol formation, and how do these impacts vary with climate change and land use practices?

3. How do newly formed aerosols grow to become important participants in chemistry/climate?

As Table I shows, these activities address the ESSL strategic priorities of exploring the role of aerosols in climate and weather and studying the impacts of megacities and urbanization.

 

Table I.  Summary of UA group research activities as they relate to ESSL strategic priorities

UA Group Activity	Megacities and the Effects of Urbanization	The Role of Aerosols in Climate and Weather
Develop new measurements for characterizing ultrafine aerosol physico-chemical properties	Better measurements of the physico-chemical properties of aerosols are needed to understand the impacts of urban emissions on regional and global climate.	Better measurements of the physico-chemical properties of aerosols are needed to understand how aerosols form, grow, and impact climate through direct and indirect radiative effects.
Investigate secondary organic aerosol (SOA) formation from biogenic precursors	The interactions between anthropogenic oxidants/emissions and biogenic trace gases are poorly understood, and may be important in SOA formation and gas-phase chemistry.	SOA formation from biogenic precursors surpasses that from anthropogenic sources and can modify cloud properties.  Cloud formation/precipitation can cause feedbacks due to their influence on biogenic emissions.
Investigate how newly formed particles grow to become important participants in chemistry and climate	New particle formation is frequently observed downwind of urban areas and may be a significant pathway for uptake and/or volatilization of organics.  It may also have implications on human health (respiratory effects) and regional photochemistry.	Understanding and modeling particle formation and growth will allow better predictions of the impact of this process on direct radiative scatter, cloud formation, and precipitation

 

 

How can we characterize the physico-chemical properties of the smallest particles in the atmosphere?

Figure 2. Flow diagram of TDCIMS particle collection and analysis

The ability to characterize the molecular constituents in nanoparticles, which is the subset of ultrafine particles whose diameters are smaller than 50 nm, is one of the greatest challenges in aerosol science.  This is because these measurements require the characterization of highly non-volatile compounds, which are generally not amenable to study.  In addition, rapid timescales for aerosol growth require measurements to be made at temporal resolutions as small as 10 minutes.  The size of these nanoparticles conspires against such efforts, since many existing instruments require micrograms of aerosol and thus require collection times of at least 3 hours.  Because of this there is still much that is not known about the species contribute to the formation and growth of particles in the atmosphere.  Without this knowledge, we cannot adequately predict the impacts of aerosols in chemistry and climate.  Meeting these challenges is of fundamental importance not only to the atmospheric sciences, but also to various engineering applications relating to the development of new materials and the control of particulate contaminates in microelectronics and nano-machine technologies. 

Click on picture to view the entire figure.


Figure 3. TDCIMS sensitivities to samples of (top) monocarboxylic and (bottom) dicarboxylic acids

To address the need for chemical composition of atmospheric nanoparticles, the UA group has teamed with Peter McMurry at the University of Minnesota to develop the thermal desorption chemical ionization mass spectrometer (TDCIMS).   The TDCIMS is an instrument that is capable of measuring the molecular composition of particles as small as 4 nm.  It accomplishes this with a sensitivity that makes it possible to measure the molecular composition of nanoparticles at ambient concentrations in the atmosphere.  Figure 2 shows a flow chart that describes TDCIMS operation.  Aerosols are first charged, then size resolved and collected by electrostatic deposition onto a platinum (Pt) filament. The collection time varies with particle size and concentration, but usually ranges from 5 – 15 min.  Then the filament is slid into the ionization region of an Atmospheric Pressure Chemical Ionization Mass Spectrometer (APCI-MS), where it is resistively heated to evaporate the particles.  The desorbed molecules are ionized by proton transfer with protonated water clusters or oxygen anions.  Ions are then transferred to a triple quadrupole mass spectrometer for mass analysis.

During 2007 the UA group has optimized their techniques for observing carboxylic acids in particles using TDCIMS, so it is now possible to detect the parent ion of a large range of these potentially important species.  Figure 3 shows a sensitivity analysis for the instrument for carboxylic acids with three to eight carbon atoms.  For reference, 1 pg of collected aerosol is commonly considered to be the detection limit for the instrument for pure compounds. Thus Figure 3 shows that the TDCIMS is close to performing at the necessary sensitivity.  A manuscript has been submitted describing this work [2].  Further developments in these techniques with other species expected in atmospheric nanoparticles are planned in 2008.

The UA group is also developing a novel instrument to measure the flux of chemically specified atmospheric particles in the 8 to 100 nm diameter range.  The approach is based on relaxed eddy accumulation (REA) sampling of atmospheric nanoparticles coupled with real-time chemical analysis of collected samples by TDCIMS.  The resulting instrument, the REA-TDCIMS, is currently being assembled and tested at NCAR by Andreas Held, a recipient of a Research Fellowship Grant by the German Research Foundation who is currently working in the laboratories of the UA group.  Additional funds have been provided by TIIMES.  Future plans for 2008 are to finish the assembly and testing of the instrument and then use it to study the formation and deposition of ultrafine aerosols at NCAR’s Marshall Field Site.

These activities in characterizing nanoparticle physico-chemical properties are supported by NSF and grants from the DOE and NOAA.

 

What are the impacts of biogenic emissions on aerosol formation, and how do these impacts vary with climate change & land use practices?

Click on picture to view the entire figure.


Figure 4. Time series of (top) particle size distribution and (bottom) meteorological observations on March 26, 2007 at Manitou Experimental Forest, showing a new particle formation event that started at 13:00 local time and coincident with a wind direction change from south (in which air masses from the Front Range metropolitan area are likely to be encountered) to north (likely dominated by biogenic emissions).

Globally, secondary organic aerosol (SOA) from biogenic precursors surpasses those from anthropogenic sources [3]. These organic particles have important impacts on climate through their direct interactions with radiation, as well as their ability to modulate cloud condensation nuclei numbers and thus cloud properties and precipitation.  These processes exert a substantial influence back upon the earth system through links to the terrestrial carbon and water cycles (e.g., precipitation regulates plant growth and thus emissions of organic compounds) [4].  The questions that currently confront researchers working in the fields of biogenic SOA and their impact on the earth system are numerous and multidisciplinary.  For example, currently lit-tle is known about the mechanism by which particles form in the atmosphere by nucleation and subsequent growth by condensation and coagulation.  Although biogenic aerosol have been observed to grow to a size that become important as cloud condensation nuclei, little is known about their ability to form cloud droplets or ice crystals [5].

The UA group is currently collaborating with researchers from ACD/BAI, TIIMES, and ASP to address the need to understand the formation of secondary organic aerosol from biogenic precursors.  Process-level studies are being conducted in the Biosphere-Atmosphere Interactions Chamber, located in the new Atmospheric Chemistry Laboratory at NCAR.  This chamber is an enhanced version of the facility used in a recent study of new particle formation from the oxidation of volatile organic compounds emitted from living vegetation [6].  The two primary components of the facility are a biogenic emissions enclosure and an aerosol growth chamber.  Experiments are initiated by continuously passing clean, dry air over a live branch in the biogenic emissions enclosure.  This sample air is fed to the aerosol growth chamber, where it is mixed with clean air containing ozone at approximately ambient concentrations; the reaction between the biogenic VOCs and ozone can lead to new particle formation and growth.  The most important accomplishment in 2007 was the expansion of the aerosol growth chamber to a volume of 10 m3.  This allows for average residence times of ~8 hours at 20 lpm sampling flow rates, which will gives sufficient time for aerosol growth to occur to a size that is pertinent to the study of cloud formation processes.  Future plans for 2008 include collaborative investigations with many university researchers.  Studies planned include one with the Jimenez group at the University of Colorado on the role that nitrogen species play in BSOA formation, and one with the Nenes group at Georgia Tech on the role of biogenic SOA in cloud formation. 

Since March 2007 the UA and BAI groups have been performing continuous measurements of ultrafine particle size distribution and some trace gases like O3 and SO2 at the Manitou Experimental Forest near Woodland Park, CO.  This research is part of the Biosphere-atmosphere Exchange of Aerosols within Cloud, Carbon and Hydrologic cycles, including Organics & Nitrogen (BEACHON) project in TIIMES.  Preliminary results indicate that new particle formation, such as the event shown in Figure 4, occurs regularly at this site. This “scoping study” is showing that there exist distinct periods where urban air is transported to the site and interacts with local biogenic emissions, as well as periods where the air masses are primarily biogenic in origin.   These measurements will continue through March 2008 in order to capture seasonal variations in aerosol size distributions.  Future plans for the site will be discussed during the BEACHON workshop to be held in Boulder, CO, in November 2007.  Possible research at the site may include expanding the measurements to include fluxes of aerosols, water vapor, nitrogen species, and organic compounds as well as characterizations of soil and plant biological activity.

Click on picture to view the entire figure.


Figure 5. (a) Time series of particle size distribution during the new particle formation event on 10 May 2007, noting with a circle the period in which the TDCIMS analysis of chemical composition of 8 nm particles shown in (b) was obtained. The spectrum in (b) shows the presence of formic acid (45 amu), acetic acid (59 amu), and other organic species.

In addition to the above activities, the past year included the longest continuous measurements of biogenic nanoparticle composition ever performed by TDCIMS.  These measurements were carried out during the EUCAARI-2007 campaign in the boreal forest in Hyytiälä, Finland from 15 April to 30 June 2007. These measurements, an example of which is shown in Figure 5, indicate a dominant role played by organic species in the formation of atmospheric nanoparticles.  Specifically, TDCIMS measurements showed the presence of methyl and dimethyl amines in particles as small as 8 nm.  Other oxidized organics detected are presumed to be multifunction organic compounds with alcohol, aldehyde, or ketone moieties and molecular weights as high as 400 amu.  TDCIMS measurements also showed the presence of multifunctional organics with carboxylic acid moieties, with molecular weights as high as 400 amu.  Changes in composition during early particle growth will also be explored, as were changes occurring during the transition from late winter to early summer.  Plans for 2008 will focus on the analysis of this comprehensive data set.

These activities in studying the physico-chemical properties of biogenic aerosols were supported by NSF and (for the EUCAARI-2007 campaign) the University of Helsinki.

 

How do newly formed aerosols grow to become important participants in chemistry and climate?

There are presently huge uncertainties in predictions of the role of aerosols in climate, especially as related to cloud formation and precipitation [7].   The use of global models to assess these impacts is at its infancy, yet one such study suggests that new particle formation can contribute up to 40% of the cloud condensation nuclei (CCN) at the boundary layer, and 90% in the remote troposphere [8].   Field observations of new particle formation and subsequent growth are needed to support such model developments. 

Click on picture to view the entire figure.


Figure 6. TDCIMS data acquired in Mexico City on March 16, 2006 during MILAGRO. The black line on the contour plot shows the particle sizes that were analyzed. Early in the event, when freshly nucleated particles were “small,” they contained primarily nitrates and organics. As time progressed, the signals for these species tended to decrease while the signal for sulfur species increased.

During 2007 the UA group has worked on the analysis of TDCIMS data acquired during the March 2006 MILAGRO campaign, in which TDCIMS measurements and particle size distributions were acquired at the ground-based “T1” site in Tecamac, Mexico.  These measurements included studies of the chemical composition of the particles in the peak of the growth mode in the size distribution during new particle formation events, as exemplified in Figure 6.  Note that on this day, nucleated particles contained far more nitrates and organics than sulfates: molar ratios of nitrate, organics and sulfur species were respectively ~50%, ~45% and ~5%, indicating that sulfur species were a relatively small fraction of the total. The TDCIMS data show that the measured organic species include methyl and dimethyl amine, organic nitrates, and organic acids. Independent calculations show that sulfuric acid condensation could have accounted for only 5-10% of the growth that was observed on this day, which is consistent with the TDCIMS measurements of composition. It follows that nitrogen compounds and organic acids must certainly contribute to the high growth rates that were observed.  Plans for 2008 include finishing the analysis of the MILAGRO data set and publishing results, and conducting further studies of the chemical composition of particles formed from nucleation in support of model development for predicting particle growth.

This work on studying the growth of freshly nucleated particles using TDCIMS measurements is supported by NSF and by grants from DOE and NOAA.

 

References
[1]	D.V. Spracklen, K.S. Carslaw, M. Kulmala, V.M. Kerminen, G.W. Mann, S.L. Sihto, Atmos. Chem. Phys., 6 (2006) 5631-5648.
[2]	J.N. Smith, G.J. Rathbone, Int. J. Mass Spectrom., submitted (2007).
[3]	J.H. Seinfeld, S.N. Pandis, Atmospheric Chemistry and Physics (John Wiley and Sons, New York, 1998).
[4]	M. Barth, J.P. McFadden, J.L. Sun, C. Wiedinmyer, P. Chuang, B. Collins, R. Griffin, M. Hannigan, T. Karl, S.W. Kim, S. Lasher-Trapp, S. Levis, M. Litvak, N. Mahowald, K. Moore, S. Nandi, E. Nemitz, A. Nenes, M. Potosnak, T.M. Raymond, J. Smith, C. Still, C. Stroud, Bull. Am. Met. Soc., 86 (2005) 1738-1742.
[5]	M.O. Andreae, P. Artaxo, C. Brandao, F.E. Carswell, P. Ciccioli, A.L. da Costa, A.D. Culf, J.L. Esteves, J.H.C. Gash, J. Grace, P. Kabat, J. Lelieveld, Y. Malhi, A.O. Manzi, F.X. Meixner, A.D. Nobre, C. Nobre, M. Ruivo, M.A. Silva-Dias, P. Stefani, R. Valentini, J. von Jouanne, M.J. Waterloo, J Geophys. Res. Atmos., 107 (2002).
[6]	T.M. VanReken, J.P. Greenberg, P.C. Harley, A.B. Guenther, J.N. Smith, 6 (2006) 4403-4413.
[7]	S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, H.L. Miller (Eds.), IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, 2007, 996 pp.
[8]	J.R. Pierce, P.J. Adams, Atmos. Chem. Phys., 7 (2007) 1367-1379.

TIIMES External Collaborators:

Kelley Barsanti, Oregon Health & Science University