Keywords: Volatile organic compounds (VOCs); Ozone (O3); Source attribution of air pollutants; GEOS-Chem; Proton Transfer Reaction Mass Spectrometry (PTR-MS)

Research tools: airborne and ground measurements, chemical transport models, inverse modeling, data analysis

Current projects

Emission and chemistry of wildfires

Understanding the chemistry in wildfire smoke has important implications for air quality, nutrient cycles, weather, and climate. We team up with scientists from four other universities (Colorado State U, CU-Boulder, U Washington, and U Wyoming) on an aircraft-based study of the emissions from western U.S. wildfire plumes. Western wildfire Experiment for Cloud chemistry, Aerosol absorption and Nitrogen (WE-CAN) campaign took place in summer 2018. Data will be collected using a wide range of instrumentation on the NSF/NCAR C-130 research aircraft. Overall we focus on three sets of scientific questions related to fixed nitrogen, absorbing aerosols, cloud activation and chemistry in wildfire plumes. This field campaign is being conducted in collaboration with the FIREX-AQ campaign supported by NOAA and NASA, which is scheduled to take place in summer 2019.

The role of our group in this project focuses on atmospheric measurements for volatile organic compounds (VOC) using a Proton-Transfer-Reaction Time-of-Flight Mass-Spectrometer (see the photos on the right), and analyzing the emission and chemical evolution of organic materials in fire plumes. Understanding the VOC chemistry and emissions of wildfires is crucial to assessing its impact on air quality and climate. In addition to the field campaign, extensive laboratory experiments will be carried out to improve the characterization of the PTR-ToF-MS instrument, particularly for those understudied VOCs.

As our continued effort into the wildfire smoke study, after the WE-CAN, we will have another intensive field campaign at Mt. Bachelor Observatory in 2019 summer. The focus of this campaign will be sampling aged fire smoke, in comparison to the fresh smoke sampled by the C-130 aircraft during WE-CAN. [UM News 2017; ABC FOX Montana news; UM News 2018; the Bozeman Daily Chronicle, NBC Montana.]

Funding: National Science Foundation (NSF)

Collaborators: WE-CAN Science Team, Bob Yokelson (U Montana), Dan Jaffe (U Washington), Qi Zhang (UC Davis)

References: Wielgasz et al. (AMS 2019); Permar et al. (AMS 2019); Permar et al. (AGU 2017); Hu et al. (2015b); Hu et al. (2015a); Hu et al. (2013); Hu et al. (2011)

WE-CAN logo

proton transfer reaction time of flight mass spectrometer

Custom-built PTR-TOF-MS (IONICON, Austria) in flight racks installed into the NSF NCAR C130 research aircraft during the WE-CAN field campaign for wildfire smoke sampling.

Permar and Hu in front of C130 during WE-CAN test flights

Permar and Hu in front of the NSF NCAR C130 aircraft after the WE-CAN test flights in Sept. 2017: where discoveries begin.

Factors controlling global tropospheric ozone

Ozone is central to our understanding of tropospheric oxidant chemistry through its driving of radical cycles. In the surface air, ozone is toxic to humans and vegetation. Ozone is also the 3rd most important greenhouse gas in the troposphere. Yet our understanding of factors determining its spatial distribution and the long-term trend is still poor. In collaboration with colleagues at Harvard and NASA GMAO, we use the atmospheric models such as GEOS-Chem chemical transport model as a platform to test our current knowledge of key factors controlling global tropospheric ozone, focusing on the following three projects:

1) Improving our understanding of global tropospheric ozone using integrated recent advancement of knowledge in isoprene chemistry, tropospheric halogen chemistry, lightning NOx source, and deep convection. This research is focused on evaluating the most recent model simulation integrating the above major model developments, against in-situ observations from ozonesonde, aircraft, and satellite to diagnose and correct model weaknesses (see the right figure for a comparison of satellite data and model prediction). This work has been featured at NASA Aura Science website.

2) Modeling global ozone concentration at very-high-resolution to improve the understandings of intercontinental transport of pollution and ozone climate forcing. This project aims to better understand the coupled effects of transport and chemical evolution on tropospheric ozone simulation over an unprecedented range of scales. For this work, we use the GEOS-Chem as a chemical module in NASA GEOS model at ~12×12 km2 resolution.

3) Investigating factors controlling the variability and trend of tropospheric ozone and OH radical over the last 30 years using the NASA Global Modeling Initiative (GMI) and GEOS-Chem chemical transport models.

Funding: National Oceanic and Atmospheric Administration (NOAA)

Collaborators: Daniel Jacob (Harvard), Christoph Keller (NASA/GSFC), Loretta Mickley (Harvard)

References: Hu et al. (2018), Hu et al. (2017), Hu et al. (AGU 2017)

Ozone concentration in the middle troposphere

Middle tropospheric ozone distribution from OMI satellite and simulated by GEOS-Chem for four seasons in 2012/2013. From Hu et al. (2017).

Ozone at 500 hPa

Above shown ozone concentration at 500 hPa on August 1, 2013 at 00:00 UTC simulated by the GEOS-5 Nature Run with GEOS-Chem chemistry at 12.5 km resolution. From Hu et al. (2018).


Atmospheric chemistry and biogenic VOCs in changing Arctic

The Arctic is experiencing rapid environmental changes due to a warming climate. Its consequences, among many, including lengthening the growing season and ecosystem transformations, are expected to increase atmospheric biogenic VOCs (BVOCs) in the Arctic, thus impacting atmospheric oxidation processes and climate. This NSF-funded project, collaborating with researchers at CU-Boulder and U Minnesota, will quantify emissions and ambient concentrations of BVOCs and other important atmospheric compositions like NOx and ozone in the Arctic tundra ecosystem (see the right map of Toolik Field Station, the site for fieldwork). Our group's role in this project is to utilize atmospheric models and the collected field data to test and improve the current understanding of the fate of air pollutants such as ozone in the changing Arctic. We will also visit Toolik Field Station in the Alaska North Slope to participate in the field campaign in 2019 summer.

Funding: National Science Foundation (NSF), U Montana 

Collaborators: Detlev Helmig (U Colorado Boulder), Dylan Millet (U Minnesota)

References: Hu et al. (2015b)

Toolik Field Station in Alaska

Location of the Toolik Field Station