Atmospheric Chemistry Group
Prof. Mark A. Zondlo
Department of Civil and Environmental Engineering
Center for Mid-Infrared Technologies for Health and the Environment
Princeton University


The Zondlo group uses novel optical instrumentation to address key questions in global climate change and air quality. New advances in optical technologies are allowing for unprecedented methods to observe the atmosphere, particularly with respect to cloud and aerosol processes which contribute the largest uncertainty to predicting future climate. We develop and deploy optical-based instrumentation using mid-infrared quantum cascade lasers and vertical cavity surface emitting lasers and analyze subsequent data to provide more accurate predictions of global climate change, air quality, and emissions of greenhouse gases.

Below is a list of current and recent projects:

Atmospheric ammonia in agricultural and urban environments

Ammonia plays critical roles in the nucleation, growth, and composition of aqueous aerosol particles that are integral in fine particle formation and urban air quality. Despite its importance to the atmospheric sciences, ammonia is surprisingly not well measured, limiting our ability to predict cloud formation and the effects of aerosols on air quality and climate. We are using a novel QC laser near 9 microns to probe atmospheric ammonia in an open-path configuration. Ammonia has similar sampling challenges as water vapor. Specifically, its mixing ratio is extremely low (parts per trillion to parts per billion levels), it readily partitions between the gas and aqueous phases, and it sticks to instrument surfaces. We have deployed the open-path sensor in urban and agricultural environments in field campaigns including NASA DISCOVER-AQ (Corolado; California; Houston, Texas) and CARE-BEIJING NCP (Beijing, China) to study ammonia emissions. This research is supported by MIRTHE.

Ammonia emissions from agriculture and urban areas create unhealthy fine particulate matter. We have developed a sensor to measure the spatial and temporal variability of ammonia to better constrain atmospheric emissions.

Nitrous oxide fluxes in ecosystems

We have developed a compact, low power, high precision (> 1 part in 1000), and high stability sensor for fast measurements of nitrous oxide, the third most important greenhouse gas. Nitrous oxide (N2O) has an atmospheric lifetime of ~ 110 years, and its emissions have tripled since the industrial revolution. Its sources are extremely heterogeneous in space and time, and thus an automated sensor is critically needed to assess the source strength from agriculture, tropical soils, permafrost, and urban emissions. The sensor is based upon quantum cascade laser technologies near 4.5 microns where carbon monoxide (CO) can also be measured as an important tracer for anthropogenic fossil fuel emissions. This research is supported by DOE, NSF, MIRTHE, and USDA

QC laser-based nitrous oxide sensor deployed in corn field to measure agricultural emission fluxes.

Fugitive methane emissions from petrochemical activities

By using our mobile laboratory in conjunction with micrometeorology measurements and boundary layer models, we are quantifying the distribution of fugitive methane emitted from gas/oil infrastructure in the Marcellus Shale. Mobile laboratories can sample a wide number of plumes emanating from gas/oil pads and compressor stations and chemically fingerprint the source (e.g. with concurrent ethane measurements), yet turning the concentrations into emission rates is challenging. Micrometeorology towers and methods provide more accurate flux estimates but are difficult to sample a large number of sites. By combining these two techniques, and then using large eddy simulation and Gaussian dispersion models, the goal of this project is to quantify the shape of the distribution of emissions in the Marcellus Shale. Highly-skewed, or fat-tailed, distributions suggest that only the largest leakers should be the focus of mitigation efforts, whereas a more normal distribution suggests that basin average measurements are representative for bottom-up inventories. This work is funded by NOAA Atmospheric Chemistry, Carbon Cycle, and Climate

Cross section of a fugitive CH4 plume.

Water vapor in the troposphere and lower stratosphere

Our group currently deploys a fast (25 Hz), open-path (minimizing sampling issues), and accurate (5-10%) water vapor sensor onboard the NSF Gulfstream-V research aircraft based upon a 1.8 micron vertical cavity surface emitting laser (VCSEL). Water vapor is the most important species in the climate and dynamics of the Earth's atmosphere, but its measurements are challenging due to its large dynamic range in concentration (one million), efficient adsorption to instrument surfaces, and difficulty calibrating at conditions of the upper troposphere and lower stratosphere. We are currently involved in global field campaigns analyzing among other things the frequency, extent, and depth of ice supersaturated regions near the tropopause. Ice supersaturated regions near the tropopause have important implications on how ice clouds nucleate as well as the trends of water in the lower stratosphere (where water vapor exhibits its strongest radiative forcing). This work is supported by NSF and NASA.

Global distribution of water vapor from the VCSEL hygrometer in our group during the HIPPO #1 deployment from the Arctic to the Antarctic in 2009.

Compact and lightweight sensor development for UAVs

The selectivity, sensitivity, and compact nature of open-path, laser-based detection schemes is particularly advantageous for deployment on unmanned aerial systems (UAS), also known as UAVs or drones. Small UAS - those with wing spans of a meter or two - provide great dexterity in profiling near-source emissions such as a well pad, pipeline, forest canopy, or an individual farm. We have developed, test flown and field deployed our sensors on a number of small UAS. We have also used such sensors on remote control aircraft to quantify methane emissions from gas/oil infrastructure in the Barnett Shale in Texas. We are currently working with Mid-Atlantic Aviation Partnership as part of the FAA-approved New Jersey, Maryland, and Virginia UAS Test Site. Funding for this work is from NSF, the Environmental Defense Fund, and NASA

Long open-path methane measurements in Alaska

Methane is an important greenhouse gas with diverse anthropogenic and natural emission sources with large spatial and temporal variability. Global climate change is accelerating natural methane emissions due to Arctic permafrost melting. The resulting formation of new Arctic thermokarst lakes contributes to significant methane ebullition (bubbling) emissions events from anoxic lake-bottom sediments. The temporal and spatial variability of these ebullition hotspot emissions are significant but have not been quantified extensively due to a lack of field measurements. We developed and deployed a long open path, quantum cascade laser-based methane sensor, demonstrating field methane measurements at Toolik Lake, Alaska.

Toolik Lake, Alaska