Welcome to the homepage of the Dahl Research Group at Loyola University Maryland.
Our research falls under the general categories of analytical chemistry, marine chemistry, atmospheric chemistry and biogeochemistry. In our group, we study the sources of alkyl nitrates in natural waters. We also are working on a variety of environmental water and air quality related projects. Most projects in our group are designed by undergraduate research students based on their interests. Some recent work and projects are outlined below.
Stony Run water quality assessment
Stony Run is an urban stream that runs through and around Loyola's Evergreen campus. Greyson Flynn (Chemistry, 2023) and Katie McManus (Biology, 2023) are current research student working on assessing the quality of the water. Their project expands upon the work of Blue Water Baltimore who works to assess other urban waterways in the city through Baltimore Water Watch and contributes to the work of the Friends of Stony Run who are stewards of the Stony Run stream valley. You can see their latest measurements on the station map and download their full results from our shared Google drive here: Water Quality Data.
Neighborhood air quality research
Take a deep breath, “our most basic common link is that we all inhabit this small planet. We all breathe the same air. We all cherish our children's future. And we are all mortal” (JFK, 1963). We all share one small planet, but we do not all inhabit the same space and we do not all breath the same air. The air that we breathe is highly variable in its quality and the health impacts of breathing polluted air have race and socioeconomic variables. Air quality can vary significantly between green spaces in cities, between areas adjacent to roadways, and those located behind vegetation barriers. We are working on assessing some of the factors that influence neighborhood air quality in north Baltimore. This project is designed to support both the commitment of the university to social justice and education as well the work of community partners in the city.
We have established a small network of particulate matter sensors in the Baltimore area. This data is available in real time from PurpleAir which has nearly 300 sensors in locations around the country and the world. Clicking on the sensor location on the map will allow you to see more detailed data for that location. Zooming out on the map will allow you to see additional PurpleAir sensors from other users. If you are interested in regional air quality, check out AirNow.gov.
Forest Patch Research
One of the benefits of urban trees is their ability to provide cooling and reduce air pollution. The city of Baltimore has hundreds of forest patches (tree canopies of at least 10,000 square feet), representing 34% of the city's tree canopy. We are partnering with Baltimore Green Space to assess the impact of some of these forest patches on local air quality. This project involves fine scale measurements of particulate matter across forest transects. Using portable Purple Air sensors, we compare the data from the forests' interiors to data collected on the edge or nearby the forest to determine if particulate matter is lower in the forest patches. To date we have worked in Govans Urban Forest, Wilson Woods, and Fairwood Forest.
Alkyl nitrate research
In our alkyl nitrate work we focus on sources of low-molecular weight alkyl nitrates to the atmosphere. In some areas of the troposphere (the lowest layer of the atmosphere), alkyl nitrates can account for up to 80% of the reactive nitrogen (NOy) present. When alkyl nitrates break down from either photolysis or reaction with OH radicals, they can generate NOx (NO+NO2) which can lead to the production of tropospheric ozone. While the sources of alkyl nitrates varies by location, a major source of low-molecular weight alkyl nitrates to the troposphere is the ocean. This leads to the question - how are alkyl nitrates formed in the oceans and water in general?
Photochemical Production in the Oceans
Previous work has shown that methyl (C1), ethyl (C2) and propyl (C3) nitrates (RONO2) are produced from the reaction of alkyl peroxy radicals with nitric oxide in water.
ROO + NO --> ROONO --> RONO2 or RO + NO2
In seawater, this reaction is initiated by photochemistry (i.e., the reaction with light) through the formation of NO from nitrite photolysis and ROO from dissolved organic matter (DOM). The reaction seems to be very dependent upon the availability of NO as well as the type of organic matter present.
At Loyola, our work has primarily focused on how variability in organic matter can affect alkyl nitrate speciation (i.e., which alkyl nitrates are formed). Observations during GOMECC, demonstrated that the proximity of the water sampled to the coast affected the relative amounts of alkyl nitrates formed compared to previous work in the open ocean. Laboratory studies with standard humic and fulvic substances confirmed that these observations were likely due to differences in organic matter between the coasts and the open ocean.
Biological Production by Phytoplankton
One of our major projects is investigating whether cultures of marine diatoms produce alkyl nitrates. Our hypothesis is that alkyl nitrates may form in cultures from the same reaction (ROO+NO). It has previously been observed that diatoms produce nitric oxide and it is thought that nitric oxide production can occur both as a function of normal growth and under stressful conditions.
In our experiments we are using chemostats to grow axenic cultures of marine diatoms in an artificial seawater version of L1 media. We primarily use two species - Thalassiosira weissfloggii & Chaetoceros muelleri. In the picture on the left (photo credit: Felisa Velasco), Christian Lewis is sampling the four chemostats. For the experimental set-up we have 3 chemostats containing cells and 1 for a chemical control since we know alkyl nitrates will be formed photochemically.
After sampling, we test for bacteria and then we measure alkyl nitrates, nitric oxide, stress via fv/fm chlorophyll and monitor pH and nutrients as well as counting cells. While our data is still preliminary, we have observed correlations of alkyl nitrates with both NO, cell count and stress.