THE IMPACT OF NOx ON OXIDATION PRODUCTS OF MONOTERPENES AND THE
SUBSEQUENT NANO-PARTICLE FORMATION AND GROWTH
C. YAN1, W. NIE2,1, A. L. VOGEL3, L. DADA1, K. LEHTIPALO1,3, D. STOLZENBURG4, F.
BIANCHI1, M.P. RISSANEN1, R. WAGNER1, M. SIMON5, M. HEINRITZI5, L. AHONEN1, M.
SIPILÄ1, J. CURTIUS5, J. KIRKBY5, U. BALTENSPERGER3, N. M. DONAHUE7, M. EHN1, D. R.
WORSNOP6,1, M. KULMALA1 and THE CLOUD COLLABORATION
1
Department of Physics, University of Helsinki, Helsinki, Finland
School of Atmospheric Sciences, Nanjing University, Nanjing, China
3
Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland
4
Faculty of Physics, University of Vienna, Vienna, Austria
5
Institute for Atmospheric and Environmental Sciences, Goethe-University of Frankfurt, Frankfurt,
Germany
6
CERN, Geneva, Switzerland
7
Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA. 8
Aerodyne Research, Inc., Billerica, MA, USA
2
Keywords: NOx, HOMs, NANO-PARTICLE FORMATION
INTRODUCTION
Atmospheric aerosol particles have a significant impact on the Earth’s climate (IPCC 2013). One
important source of these particles is the formation and subsequent growth of new aerosol particles
directly in the atmosphere (secondary aerosol), which potentially has a large contribution to the budget of
cloud condensation nuclei (CCN) on a global scale (Merikanto et al., 2009; Dunne et al., 2016).
In the past decade, organic vapors have been recognized as an important source of secondary aerosol
mass, through the condensation of their various oxidation products on pre-existing particles (Jimenez et
al., 2009). Recent chamber studies have shown that some oxidized products with very low volatility can
contribute to the initial growth of newly formed particles (Ehn et al., 2014, Tröstl et al., 2016), and even
participate in the nucleation process (Kirkby et al., 2016). Alpha-pinene, a common monoterpene, was
chosen as the VOC (Volatile Organic Compound) precursor in the abovementioned studies, as it is one of
the most abundant biogenic VOCs globally, especially in high-latitude regions. After the initiation of
oxidation by O3 and/or OH, the intermediate products may undergo fast auto-oxidation until a termination
reaction occurs, forming highly oxidized multifunctional compounds (HOMs) (Ehn et al., 2014, Jokinen et
al., 2015, Rissanen et al., 2015).
The ubiquitous nitrogen oxides (NOx) in the atmosphere have a significant influence on the VOC
oxidation, through reacting with peroxy radicals or initiating the oxidation by NO3, leading to various
products, many of which are nitrogen-containing compounds (Hallquist et al., 2009). Even in remote or
rural areas, such as the SMEAR II station in southern Finland (Hari and Kulmala, 2005), where the mixing
ratios of NOx are very low (hourly average NO2 concentration ≈ 1ppb and NO concentration ≈ 50 ppt),
NOx still has a strong influence on the HOM production (Yan et al., 2016, Lee et al., 2016). Accurate
aerosol modelling requires a better understanding of the extent that NOx modifies the oxidation pathways,
as well as detailed information of the oxidation products.
The ultra-clean CLOUD chamber (Kirkby et al., 2011, Duplissy et al., 2016), which is equipped with
state-of-the-art instruments, allows the study of HOM production and aerosol formation under
atmospherically relevant levels of NOx. By identifying the HOMs produced under various NOx conditions,
we deduced their plausible reaction pathways. We further characterized the growth rate of newly formed
particles to study the effect of NOx on aerosol particle formation.
METHODS
We studied the effect of NOx on HOM production and aerosol formation in the CERN CLOUD chamber
during the CLOUD10 campaign in fall 2015. Two most globally abundant monoterpenes, alpha-pinene
and delta-3-carene, were used as the VOC precursors. We varied their total concentration from 300 to
1200 ppt, while keeping their initial ratio constant at 2:1. As sulphuric acid (SA) is known as an important
contributor to aerosol formation, to better mimic the atmospheric particle growth, we also added 0.6 - 3.3
ppb of SO2, which produced about 0.5 – 2 ppt SA. We refer to each monoterpene-SA concentration pair as
one run. During each run, we injected three levels of NO into the chamber, most of which was quickly
converted into NO2 by O3, and a small fraction of NO2 was further oxidized to NO3. The NOx (NO+NO2)
concentration was measured as 0 – 5.2 ppb with a constant ratio between NO and NO2 (at ca. 0.6%).
We characterized the HOM production and nano-particle formation and growth in this SA-monoterpeneNOx 3-dimensional parameter space with various instruments. A time-of-flight chemical ionization mass
spectrometer (tof-CIMS, also known as CI-APi-TOF) using nitrate as the reagent ion was used to measure
the composition and concentration of sulfuric acid as well as highly oxidized products from monoterpenes
(Jokinen et al., 2012, Ehn et al., 2014). Another tof-CIMS equipped with a FIGAERO sampling inlet,
using iodide (I-) as the reagent ion, was used to measure the chemical composition of the aerosol particles
and the desorption temperature of these compounds. In addition, we deployed a set of instruments to
measure size-segregated particle formation and growth, including a PSM (particle size magnifier,
Vanhanen et al. 2011), a DMA-Train (Stolzenburg et al. 2016), a NAIS (Mirme and Mirme, 2013), and a
TSI nano-SMPS.
CONCLUSIONS
Figure 1 exhibits a typical run sequence when the concentration of NO was increased stepwise into the
chamber. The time evolution of some example HOMs is shown in the bottom panel, each of which
instantaneously responded to the NOx changes in different ways, suggesting multiple reaction pathways
were influenced or created by NOx. Such changes in HOMs had pronounced influence on aerosol
formation. As shown in the top panel, the aerosol formation was significantly suppressed when adding
NOx.
Figure 1. Temporal evolution of representative HOMs (bottom panel) and particle size distribution (top
panel) when various levels of NOx (middle panel) and ion concentrations (not shown) were present in the
chamber.
We will present more detailed information on the identities of various NOx-relevant oxidation products
and their plausible formation pathways that are deduced based on their elemental compositions as well as
their responses to NOx variation. We will show to what extent the chemical processes observed in our
chamber study can be found in the atmosphere. By characterizing the properties of such NOx-relevant
products, we will attempt to explain the negative effect of NOx on nano-particle formation.
ACKNOWLEDGEMENTS
We thank CERN for supporting CLOUD with important technical and financial resources, and for
providing a particle beam from the Proton Synchrotron. This research received funding from the EC
Seventh Framework Programme (Marie Curie Initial Training Network "CLOUD-ITN" no. 215072, MCITN "CLOUD-TRAIN" no. 316662, and ERC-Advanced "ATMNUCLE'' grant no. 227463), European
Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant
agreement No. 656994 (nano-CAVa), the German Federal Ministry of Education and Research (project
nos. 01LK0902A and 01LK1222A), the Swiss National Science Foundation (project nos. 200020_135307
and 206620_130527), the Academy of Finland (Center of Excellence project no. 1118615, projects
135054, 133872, 251427, 139656, 139995, 137749, 141217, 141451, 299574), the Finnish Funding
Agency for Technology and Innovation, the Nessling Foundation, the Austrian Science Fund (FWF;
project no. P19546 and L593), the Portuguese Foundation for Science and Technology (project no.
CERN/FP/116387/2010), the Swedish Research Council, Vetenskapsrå̊det (grant 2011-5120), the
Presidium of the Russian Academy of Sciences and Russian Foundation for Basic Research (grants 08-0291006-CERN and 12-02-91522-CERN), and the U.S. National Science Foundation (grants AGS1136479
and CHE1012293). .
REFERENCES
Dunne, E., et al. (2016). Global atmospheric particle formation from CERN CLOUD measurements.
Science 354(6316): 1119-1124.
Duplissy, J., et al. (2016). Effect of ions on sulfuric acid-water binary particle formation: 2. Experimental
data and comparison with qc-normalized classical nucleation theory. Journal of Geophysical Research:
Atmospheres 121: 1752–1775.
Ehn, M., et al. (2014). A large source of low-volatility secondary organic aerosol. Nature 506: 476-479.
Hallquist, M., et al., (2009). The formation, properties and impact of secondary organic aerosol:
current and emerging issues. Atmospheric Chemistry and Physics 9(14): 5155-5236.
Hari, P. and M. Kulmala (2005). Station for measuring ecosystem- atmosphere relations, Boreal Environ.
Res. 10, 315–322.
IPCC: Climate Change 2013: the Physical Science Basis. Contribution of Working Group I to the Fifth
Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press,
Cambridge, UK, and New York, NY, USA.
Jimenez, J., et al. (2009). Evolution of organic aerosols in the atmosphere. Science 326:1525-1529.
Jokinen, T., et al. (2014). Rapid Autoxidation Forms Highly Oxidized RO2 Radicals in the Atmosphere.
Angewandte Chemie International Edition 53(52): 14596-14600.
Jokinen, T., et al. (2015). Production of extremely low volatile organic compounds from biogenic
emissions: Measured yields and atmospheric implications. Proceedings of the National Academy of
Sciences 112: 7123-7128.
Kirkby, J., et al. (2016). Ion-induced nucleation of pure biogenic particles. Nature 533: 521–526.
Lee B., et al (2016). Highly functionalized organic nitrates in the southeast United States: Contribution to
secondary organic aerosol and reactive nitrogen budgets. Proceedings of the National Academy of
Sciences 113: 1516-1521.
Merikanto, J., et al. (2009). Impact of nucleation on global CCN. Atmospheric Chemistry and Physics
9(21): 8601-8616.
Mirme, S. and A. Mirme (2013). The mathematical principles and design of the NAIS – a spectrometer for
the measurement of cluster ion and nanometer aerosol size distributions, Atmospheric Measurement
Techniques 6: 1061–1071.
Riccobono, F., et al. (2014). Oxidation products of biogenic emissions contribute to nucleation of
atmospheric particles. Science 344(6185): 717-721.
Rissanen, M. P., et al. (2014). The Formation of Highly Oxidized Multifunctional Products in the
Ozonolysis of Cyclohexene. Journal of the American Chemical Society 136(44): 15596-15606.
Stolzenburg, D., G. Steiner, and P. M. Winkler (2016). A DMA-train for precision measurement of sub
10-nm aerosol dynamics, Atmospheric Measurement Techniques Discussions., doi:10.5194/amt-2016-346,
in review.
Tröstl, J., et al. (2016). Low-volatility organic compounds are key to initial particle growth in the
atmosphere. Nature 533: 527–531.
Vanhanen, J. et al. (2011). Particle size magnifier for nano-CN detection. Aerosol Science and Technology
45:533–542.
Yan C., et al (2016). Source characterization of highly oxidized multifunctional compounds in a boreal
forest environment using positive matrix factorization. Atmospheric Chemistry and Physics 16: 1271512731.