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Impact of NOx and OH on secondary organic aerosol formation from beta-pinene photooxidation

Sarrafzadeh, M., Wildt, J., Pullinen, I., Springer, M., Kleist, E., Tillmann, R., Schmitt, S. H., Wu, C., Mentel, T. F., Zhao, D., Hastie, D. R., and Kiendler-Scharr

Published September 2016 in Atmos. Chem. Phys., 16, 11237-11248, doi:10.5194/acp-16-11237-2016.

Abstract. In this study, the NOx dependence of secondary organic aerosol (SOA) formation from photooxidation of the biogenic volatile organic compound (BVOC) β-pinene was comprehensively investigated in the Jülich Plant Atmosphere Chamber. Consistent with the results of previous NOx studies we found increases of SOA yields with increasing [NOx] at low-NOx conditions ([NOx]0  <  30 ppb, [BVOC]0 ∕ [NOx]0  >  10 ppbC ppb−1). Furthermore, increasing [NOx] at high-NOx conditions ([NOx]0  >  30 ppb, [BVOC]0 ∕ [NOx]0  ∼  10 to  ∼  2.6 ppbC ppb−1) suppressed the SOA yield. The increase of SOA yield at low-NOx conditions was attributed to an increase of OH concentration, most probably by OH recycling in NO + HO2  →  NO2 + OH reaction. Separate measurements without NOx addition but with different OH primary production rates confirmed the OH dependence of SOA yields. After removing the effect of OH concentration on SOA mass growth by keeping the OH concentration constant, SOA yields only decreased with increasing [NOx]. Measuring the NOx dependence of SOA yields at lower [NO] ∕ [NO2] ratio showed less pronounced increase in both OH concentration and SOA yield. This result was consistent with our assumption of OH recycling by NO and to SOA yields being dependent on OH concentrations. Our results furthermore indicated that NOx dependencies vary for different NOx compositions. A substantial fraction of the NOx-induced decrease of SOA yields at high-NOx conditions was caused by NOx-induced suppression of new particle formation (NPF), which subsequently limits the particle surface where low volatiles condense. This was shown by probing the NOx dependence of SOA formation in the presence of seed particles. After eliminating the effect of NOx-induced suppression of NPF and NOx-induced changes of OH concentrations, the remaining effect of NOx on the SOA yield from β-pinene photooxidation was moderate. Compared to β-pinene, the SOA formation from α-pinene photooxidation was only suppressed by increasing NOx. However, basic mechanisms of the NOx impacts were the same as that of β-pinene.

Stable carbon isotope ratios of ambient aromatic volatile organic compounds

Anna Kornilova, Lin Huang, Marina Saccon, and Jochen Rudolph

Published September 21, 2016 in Atmos. Chem. Phys., 16, 11755-11722.

Abstract. Measurements of mixing ratios and stable carbon isotope ratios of aromatic volatile organic compounds (VOC) in the atmosphere were made in Toronto (Canada) in 2009 and 2010. Consistent with the kinetic isotope effect for reactions of aromatic VOC with the OH radical the observed stable carbon isotope ratios are on average significantly heavier than the isotope ratios of their emissions. The change of carbon isotope ratio between emission and observation is used to determine the extent of photochemical processing (photochemical age,  ∫ [OH]dt) of the different VOC. It is found that  ∫ [OH]dt of different VOC depends strongly on the VOC reactivity. This demonstrates that for this set of observations the assumption of a uniform  ∫ [OH]dt for VOC with different reactivity is not justified and that the observed values for  ∫ [OH]dt are the result of mixing of VOC from air masses with different values for  ∫ [OH]dt. Based on comparison between carbon isotope ratios and VOC concentration ratios it is also found that the varying influence of sources with different VOC emission ratios has a larger impact on VOC concentration ratios than photochemical processing. It is concluded that for this data set the use of VOC concentration ratios to determine  ∫ [OH]dt would result in values for  ∫ [OH]dt inconsistent with carbon isotope ratios and that the concept of a uniform  ∫ [OH]dt for an air mass has to be replaced by the concept of individual values of an average  ∫ [OH]dt for VOC with different reactivity.

Prof. Robert McLaren is accepting applications for graduate students and Post Docs

Prof. Robert McLaren is currently accepting applications for graduate students in atmospheric chemistry.

Prof. McLaren is also accepting applications for a post-doctoral position, with a focus on aerosol formation studies in collaboration with Environment Canada. Experience with aerosol mass spectrometry, PTR/MS and physical measurements of aerosols is an asset.

The 25th Annual Harold I Schiff Lecture Faculty of Science: Presented by Prof. Dr. Ulrich Platt

Institute of Environmental Physics
Heidelberg University
Quantification of Volcanic Gas Emission by Optical Spectroscopy - How and Why

Thursday, June 16, 2016, 2:30 PM
103 Life Science Bldg.
York University

Prof. Dr. Ulrich Platt

Prof. Dr. Ulrich Platt

: Volcanoes play an enormous role for the Earth system and for our atmosphere. Therefore, volcanic gas emissions are studied not only out of scientific curiosity. In addition to their influence on the atmosphere composition and emission rate of volcanic gases are a window to processes occurring in the Earth’s interior, also volcanic eruptions forecast can be improved by measuring variations of gas emissions    ratios e.g. CO2/SO2 or BrO/SO2. In recent years spectroscopic quantification of gas emissions from volcanoes and other sources made enormous progress. In particular passive spectroscopic approaches observing volcanic gases based on their observation of scattered sun-light in the ultra-violet (UV) spectral range evolved from an art to mature techniques. For instance UV spectrometers form the Continue reading


Faculty of Graduate Studies
Graduate Programme in Chemistry
Kevin Marshall Nikelski
A Candidate for the Degree of Master of Science.

Title of Thesis:
Exploring the Potential of Polyelectrolyte-Apatmer Films for Use in Optical and Electrochemical Sensing (Thesis)

Public Talk: Monday, March 14, 2016, 2:30 PM,  PSE 317

Nitrogen oxides (NOy) are key oxidative species within the nocturnal atmosphere, due to reduced OH mixing ratios during nocturnal hours. NOy species have also been found to serve as a source of radical production in the early morning. When coupled with their impact upon air quality and climate, the study of NOy serves as important undertaking Continue reading


Faculty of Graduate Studies Graduate Programme in Chemistry
Yasamin Hassani
A Candidate for the Degree of
Master of Science

Title of Thesis:
Method Development for Concentration Measurements of SVOCs and Analysis of Ambient Samples (Thesis)

Public Talk: Thursday, Sept. 24th, 2015, Room 317 Petrie


Semi-volatile organic compounds (SVOCs) comprise a wide range of toxic pollutants in the atmosphere. Phenols, polycyclic aromatic hydrocarbons (PAHs) and n-alkanes are specific examples of SVOCs that are the focus of this project. SVOCs are compounds with intermediate vapour pressures and can exist in the atmosphere in both gas phase and in particulate matter (PM), which makes their quantification in the atmosphere challenging. Therefore, developing a well-characterized analytical technique for accurate concentration measurement of the selected classes of SVOCs is essential in order to gain more insight into their ambient yield and environmental fate. Recently, a new methodology that allows sampling and analysis of the total (gas phase and PM) concentration of SVOCs in the atmosphere has been developed and tested on a class of SVOCs, namely, nitrophenols (Busca, 2010; Moukhtar et al., 2011; Saccon et al., 2013). This method is based on a sorbent impregnated filter (SIF) technique using conventional high volume air samplers, extraction and analysis by GC-MS.

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Faculty of Graduate Studies Graduate Programme in Chemistry

Ibraheem Nuaaman:
A Candidate for the Degree Doctor of Philosophy

Title of Thesis:
Investigation of air pollutants near the Great Lakes in Ontario and along the coast of California

Public Talk: Monday, April 20th, 2015, 1:30 - 2:15 PM., Room 317 PSE


Carbonyl measurements in rural Ridgetown, Ontario using an AT-DNPH-HPLC system during the BAQS-Met study (2007) will be discussed. An overview of the significance, source and sinks of carbonyls will be given. Principle of operation and calibrations for the AT-DNPH-HPLC system will be presented. Total carbonyl mixing ratios were observed to be few ppb. Carbonyls accounted for 22% of the non-methane hydrocarbon (NMHC) distribution and aldehyde contribution to NMHC reactivity towards OH radical was 37%. The net photochemical formation rate (S-L) was estimated and compared to the maximum observed formation established from diurnal profiles. The HCHO to CH3CHO ratio revealed that carbonyl precursors are largely anthropogenic in nature. Continue reading

The 24th Annual Harold I Schiff Lecture Faculty of Science: Presented by Steven S Brown

NOAA Earth System Research Laboratory
and Department of Chemistry, University of Colorado

The Atmospheric Chemistry of Winter

Thursday, May 28, 2015, 2:30 PM

103 Life Science Bldg.
York University

Abstract: The study of lower atmospheric chemistry, at least at northern mid-latitudes where a large fraction of the world’s population resides, has largely been a story of summertime phenomena. Rapid, summertime photochemical oxidation converts primary emissions into secondary pollutants, such as ozone and aerosols, in regions very near the emission sources, leading to significant impacts on air quality and human health. Winter oxidative processes tend to be much slower, allowing for wider dispersion of primary pollutants and generally weaker air quality impacts in the immediate vicinity of source regions. Yet there remain interesting and important chemical cycles that are Continue reading

HONO-Measurements During the OS Field Campaign at AMS13

Informal Lunchtime Atmospheric Chemistry Discussion Series
Presented by:
Kevin Nikelski, Graduate Student
April 7th, 2015 at Noon - 1PM
317 Petrie Science and Eng. Bldg.

Description: Nitrous acid (HONO) is of particular relevance to atmospheric chemistry in regards to its significant contribution to photochemical production of the OH radical, which serves as the main daytime oxidant in the troposphere. Many studies have reported observing significant HONO mixing ratios during daylight hours, which could be due to an as yet unexplained continuous daytime source and/or indicating a method of HONO uptake and storage during the night with subsequent release the next day. In this talk, I will discuss HONO measurements from Aug 17th- Sept 11th during the OS field campaign in the region near Fort McMurray Alberta at the AMS13 ground site. Continue reading