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Research

Research Areas

Research in our group applies a range of analytical techniques to address questions about the processes that control the composition of the atmosphere. Our focus is on acquiring and interpreting field measurements of concentrations and fluxes, but we also do some work with monitoring data and collaborate extensively with modelers.

Most of our research falls under the four broad themes:

  • Measurements of ammonia and particle composition
  • Atmosphere-biosphere exchange of trace gases and particles
  • Fate of organonitrogen in the atmosphere
  • Observational constraints on urban air quality and greenhouse gas emissions

 

Measurements of ammonia and particle composition

A significant focus in the group has been to develop the analytical capability to accurately measure ammonia (NH3) in the atmosphere, where it is the most important alkaline gas phase molecule. Our spectroscopic approach using an Aerodyne QCL is highly selective and sensitive, even in high humidity conditions (Ellis et al., 2010) and the results of an international intercomparison campaign (von Bobrutzki et al., 2010) indicate that it is among the most accurate and precise instruments for NH3 in the world. Our adaptation of a commercial online sampling system (AIM-IC) for water-soluble gases, including ammonia, and particulate matter (Markovic et al., 2012) has been a ‘workhorse’ instrument for the group. By providing high-quality NH3 observations that can be used to evaluate regional and global chemical transport models, we are helping to improve the understanding of NH3 emission and deposition, and its role in particle formation and growth.
 
Our observations at Bakersfield during the summer 2010 CalNex air quality field campaign showed that NH3 was in great excess compared to the inorganic acids. The QCL was deployed during the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPE) to measure vertical profiles of NH3 in the lowest 300 m of the atmosphere and found that the shape and magnitude of the diurnal cycle varied with height (Tevlin et al., 2017). During the Utah Winter Fine Particle Study (UWFPS) in 2017, we measured NH3 onboard a Twin Otter (Moravek et al., in prep) and on the ground in Salt Lake City (Hrdina et al., in prep) and found surprisingly high levels for a cold wintertime atmosphere, which contributes to high particle mass loadings in the region. Using simultaneous measurements of PM2.5 components and gas phase NH3 and HNO3, we can provide robust observational constraints on particle acidity (Murphy et al., 2017).
 

Our involvement in the collaborative and interdisciplinary NETCARE project has provided a unique opportunity to explore NH3 in the remote polar atmosphere. Our observations of neutralized particles and relatively high levels of NH3 in the Arctic marine boundary layer in 2014 allowed us to identify a significant role for colonies of migratory seabirds to impact the composition of the Arctic marine atmosphere (Wentworth et al., 2016). Using a chemical transport model with detailed aerosol microphysics, these seabird emissions are found to exert a very strong control on the radiative forcing of the Arctic atmosphere, suggesting the potential for climate feedbacks (Croft et al., 2016). In 2016, we returned to the Arctic, measuring ammonia both from the icebreaker and at Alert, and have intriguing evidence that the tundra can also act as a source of ammonia to the Arctic atmosphere (Wentworth and Moravek, in prep).   

 
 

Atmosphere-biosphere exchange of trace gases and particles

Our group has pursued a number of projects that directly or indirectly measure surface-atmosphere exchange of reactive nitrogen and other atmospheric constituents. Our initial work was carried out at Haliburton Forest, a region that historically received very large reactive nitrogen inputs, making it an ideal location to study links between the carbon cycle, nutrient inputs, and management practices. During the summer and fall of 2011, we found evidence of net uptake of CH4 in the tower footprint and identified soil moisture and wind speed as the key controls on the magnitude of the flux (Wang et al, 2012). Continuous measurements of CO2 fluxes from 2010 through 2012 demonstrate that the tower footprint typically represents a small source of carbon annually, but that a 3-day heatwave in May 2010 that severely damaged emerging leaves resulted in significant carbon losses over that year’s growing season (Geddes et al., AgForMet, 2014). Eddy covariance measurements of size-resolved particle fluxes made in the summer and fall of 2011 showed that particle size, leaf area index and atmospheric stability were all important controls on the direction and magnitude of particle fluxes (Petroff et al., 2018). At both Haliburton and the University of Michigan Biological Station (UMBS), we measured eddy covariance fluxes of nitrogen oxides during the summers of 2011 and 2012, respectively, and found that dry deposition accounted for 22 and 40% of the total NOy deposition at the sites. In 2016, we returned to UMBS as part of the PROPHET-AMOS campaign, where we focused on simultaneous above-canopy measurements of NO and NO2 fluxes. Our observations, along with 1D canopy modelling, carried out in collaboration with Allison Steiner, indicate that emissions of NOx from the local ecosystem in very small, and that a ‘morning pulse’ of NOx observed on polluted days can be attributed to the photochemical conversion of NOz to NOx (Shi, Kavassalis et al., in prep). 

N-containing trace gases like HONO and NH3 have microbial and abiotic sources and sinks within terrestrial ecosystems, making predictions of their rates of emission and deposition challenging. During field campaigns in Colorado and California, we found evidence of a soil reservoir for HONO (VandenBoer et al., 2013, VandenBoer et al., 2014), and performed laboratory flow tube studies using soil surrogates and field samples to confirm that HONO can be taken up by carbonate-containing minerals and subsequently displaced by stronger photochemical acids (VandenBoer et al., 2015). This work is significant because it provides another possible explanation for the missing source of HONO during the daytime, which contributes to the oxidative capacity of the atmosphere. Our observations during CalNex were also used in Pusede et al., 2015, who showed that while NO2 is significantly lower on weekends, there is no evidence of lower HONO production on weekends.
 
During the Border Air Quality and Meteorology Study (BAQS-Met) in southern Ontario, our analyses indicated that the magnitude (and even direction) of modelled ammonia surface fluxes is incorrect (Ellis et al., 2011), and that this causes significant biases in model predictions of the mass loading of fine particles, a criteria air pollutant (Markovic et al., 2011). Using the bidirectional flux framework and simultaneous measurements of soil and atmospheric chemistry in a subsequent field study, we were able to show that an unmanaged grassland transitioned from a source to a sink of ammonia between summer and fall (Wentworth et al., 2014). The inclusion of bi-directional ammonia fluxes in Environment Canada’s air quality model also resulted in a much better agreement with our measurements of ammonia during a field campaign in the Alberta Oil Sands region (Whaley et al., 2018). A common observation from our group and others is a sharp increase in NH3 mixing ratios shortly after sunrise; however, this feature is typically not simulated by chemical transport models. In collaboration with Jeff Collett (CSU), we used lab and field measurements of dew to provide direct evidence that substantial amounts of ammonia can accumulate in dew overnight and the subsequent evaporation of dew in the morning leads to an intense burst of NH3 into the near-surface atmosphere (Wentworth et al., 2016). 
 
Ongoing work in focused on measurements of reactive nitrogen exchange in agricultural environments. In 2017 and 2018, we have collaborated with Elizabeth Pattey at Agriculture and Agri-food Canada to measure fluxes of NH3 above fertilized corn fields across the entire growing season. Preliminary results indicate that even in fertilized fields, bi-directional exchange of ammonia is prevalent (Moravek et al., in prep).
 
 

Fate of organonitrogen in the atmosphere 

While ammonia is the most abundant form of reduced nitrogen, many other types of organic reduced nitrogen are emitted to the environment from natural, agricultural and industrial sources. We developed an online method for measurements of the organic analogues of ammonia, alkyl amines, in the gas and particle phases (VandenBoer et al., 2012). By combining size-resolved daily integrated samples of amines in particulate matter with online hourly measurements of amines in the gas and particle phases, we were able to show that amines are present at much lower levels than ammonia in the gas and bulk particle phase. However, as one moves to increasingly small particle sizes, amines can become more significant, implying that they may play a more significant role in the early stages of particle growth, or that they are reacted away during particle aging (VandenBoer et al., 2011).

In collaboration with Jon Abbatt’s group, we carried out smog chamber measurements of the oxidation of ethanolamine (a benchmark solvent for carbon capture and sequestration) and found a short lifetime against photochemical oxidation, a process that produces a gas phase amide (Borduas et al., 2013). Further experimental and theoretical work investigated the kinetics, mechanism, and products of amide oxidation, showing that the toxic isocyanates are common products (Borduas et al., 2015). We revisited the pH-dependent hydrolysis kinetics of HNCO and provided the first temperature-dependent solubility measurements for this compound (Borduas et al., ACP, 2016). Having identified HNCO and the “CO2 of organonitrogen” (i.e. the final product of atmospheric oxidation), we are now carrying out kinetics experiments to identify possible aqueous phase reaction pathways for HNCO that may be more important than hydrolysis alone. We are also studying condensed phase reactions of reduced nitrogen from the perspective of their influence on the reactive nitrogen budget, a complementary perspective to the interest of others in the production and loss of ‘brown carbon’.

 

Observational constraints on urban air quality and greenhouse gas emissions

More than 80% of Canadians live in urban areas, and these regions of intensive human activity result in concentrated emissions of air quality pollutants and greenhouse gases. Across the world, cities are looking for strategies to reduce emissions to protect public health and mitigate climate change. We have exploited observational data from long-term monitoring networks to identify which precursor emission reductions will be most effective in decreasing the secondary pollutant ozone, and how chemistry and meteorology interact to contribute to poor air quality (Geddes et al., 2009, Pugliese et al., 2014, Wentworth et al., 2015).We developed a unique high-resolution Southern Ontario CO2 Emission inventory (SOCE) and evaluated it against monitoring data by working with Environment and Climate Change Canada to simulate urban scale CO2concentrations in GEM-MACH (Pugliese et al., 2018). Our next step is to make simultaneous measurements of CO2, CO, CH4, NO, NO2, N2O and NH3 in the urban environment and use enhancement ratios between the different pollutants to understand the relative importance of emissions from different source sectors (e.g. cars, trucks, power plants, wastewater treatment).

Analytical Techniques

 

Ambient Ion Monitor/Ion Chromatograph (AIM-IC)

Quantum Cascade Tunable Infrared Laser Differential Absorption Spectroscopy (QC-TILDAS)

Chemiluminescent detection system for NO/NO2/NOy

Capable of highly sensitive, continuous and simultaneous measurements of atmospheric acidic and alkaline soluble gases and aerosol constituents.

Capable of making sensitive, high time resolution measurements of ammonia in a wide variety of environments.

Makes sensitive, high time resolution measurements of atmospheric NOxspecies and total reactive nitrogen oxides (NOy).
 
 
 

Field Campaigns


UMBS-PROPHET 2012, 2016

We have made measurements of nitrogen oxide mixing ratios and fluxes in two summer campaigns at the University of Michigan Biological Station’s Program for Research on Oxidants: PHotochemistry, Emissions, and Transport (PROPHET) tower. During the summer of 2016, we were part of a large collaborative effort to study oxidants in a biogenic-rich environment. Sarah Kavassalis is collaborating with Allison Steiner (University of Michigan) to perform 1D modelling of the canopy turbulence and chemistry.

UBWOS 2014

The Uintah Basin Winter Ozone Study (UBWOS) campaign took place in January-February of 2014. Angela Hong brought our 2-channel NOx/NOy chemiluminescence analyzer to Horse Pool Utah to study vertical profiles of nitrogen oxides and ozone in the snowpack. The data will be analyzed to better understand the roles of the snowpack in the recycling of nitrogen oxides and radicals in the region. Angela wrote a more detailed description of her experience in an Environmental Chemistry blog.

NETCARE


The Network on Climate and Aerosols (NETCARE) is large collaborative project (PI Jon Abbatt) aimed at addressing key uncertainties related to aerosols in remote Canadian environments, funded by the Climate Change and Atmospheric Research program at NSERC.  In the summer of 2014, the Murphy group operated the AIM-IC onboard the CCGS Amundsen while the vessel sailed through the Canadian Arctic. We measured high levels of gas phase ammonia that we were able to associate with biomass burning and emissions from migratory seabird colonies. In the summer of 2016, we brought the AIM-IC to Alert, and our QC-TILDAS instrument on board the Amundsen to learn more about water-soluble particles and gases in the Arctic.

FOSSILS 2013


The Fort McMurray Oil Sands Strategic Investigation of Local Sources (FOSSILS) campaign took place in August-September of 2013. The Murphy group was involved in measurements from the AMS 13 ground site, located near Fort McKay. We operated the AIM-IC instrument to make measurements of water-soluble PM2.5 and gas phase NH3, HNO3, and SO2. We also assisted Environment Canada with the operation of a PTR-TOF-MS for the measurement of volatile organic compounds. The data have been analyzed to better understand the sources and fates of emissions from Oil Sands industrial activity.

Haliburton Forest 2008-2013

Haliburton Forest and Wildlife Reserve is a privately-owned mixed hardwoord forest located 200 km northeast of Toronto. We have been making flux measurements from a 32 m tower located in Haliburton Forest since 2009. Our primary interests are the greenhouse gas and reactive nitrogen budgets of the forest.
In the summer of 2011, we made intensive measurements of the canopy-scale fluxes of methane, nitrogen oxides and particulate matter. Our analysis of the carbon dioxide fluxes between 2009 and 2013 indicate that the area around the tower is a negligible sink of carbon, and that a short heatwave in the spring of 2010 led to persistent loss of carbon throughout that summer.

CalNex 2010


The California Nexus (CalNex) campaign took place in California in the summer of 2010, with the objective of understanding issues that relate air quality and climate change. The Murphy group was involved in measurements of gas phase NH3 at the Pasadena ground site, and water-soluble PM2.5 and precursor gases at the Bakersfield ground site. Check out our publications page to see how these data have been used to better understand gas-particle partitioning and particle formation in southern and central California.

BAQS-Met 2007


The Border Air Quality and Meteorology Study (BAQS-Met) took place in June-July 2007, with the objective of understanding the impacts of transboundary transport and local emissions on air quality in southwestern Ontario. The Murphy group was involved in measurements of gas phase NH3 and water-soluble PM2.5 at the Harrow ground site. Many of the results from this study have been published in a special issue of Atmospheric Chemistry and Physics.

 

Data Analysis

In addition to analysis of data obtained in our group, we have support from Environment Canada to analyze observations from many federal and provincial monitoring networks (e.g. NAPS, CAPMON)

Ozone in GTA 

An examination of the last decade of observations of ozone and its precursors in the Greater Toronto Area has demonstrated why emission controls that have been so successful for primary pollutants have resulted in only minor reductions in photochemical ozone. This figure displays contours of predicted ozone production rates as a function of NO2 concentration and VOC reactivity, while the shaded arrow shows the chemical space over which the atmosphere has changed in the last eight years, resulting in minimal decreases in ozone.

Acid Deposition in Canada

Our analysis of the chemical composition of gases, particulate matter and precipitation from CAPMON sites across Canada between 1990 and 2007 found that decreases in sulphate yielded increases in the pH of precipitation, but also altered the partitioning between HNO3 and particulate nitrate. The lack of routine measurements of gas phase ammonia complicates the interpretation of trends and underlines the need for the type of accurate measurements we are pursuing.


Ground-based evaluation of OMI NO2

Applications of remotely sensed chemical composition data include evaluation of air quality models, assimilation into air quality forecast models, identification of previously unrecognized pollution hot spots or emission sources, and assessments of chronic pollutant exposure in epidemiological studies. There is interest in ascertaining to what degree observations of tropospheric columns of pollutants (e.g. NO2) observed from space can replicate/replace data from sparse networks of traditional in situ monitors, particularly in urban areas where there is a high degree of spatial variability. One caveat is the presence of clouds, which obscure the satellite instrument’s field of view. We are assessing this by using the fractional cloud cover observed by the Ozone Monitoring Instrument (OMI) to screen the ground-based measurements, and calculate whether there is a significant selection bias in NO2 and SO2.