Quantifying and Reducing Nitrogen Footprints of Urban Areas: A Case Study for Baltimore, Maryland

Reactive nitrogen (Nr; all N species except N2) is created by the Haber-Bosch process for food production and is created as a by-product of fossil fuel combustion as well as a number of other natural processes. While it is vital for food production, too much Nr has a negative effect on the environment. Calculating its amount released to the environment as a result of an entities’ resource use is useful for managing the amount of excess Nr in the environment. Footprints both provide a baseline for understanding N losses and are used to identify reduction strategies. The nitrogen (N) footprint tool for both individuals and institutions allows each of these entities to do that. Individuals use the personal N footprint calculator to calculate the N impacts of their daily activities. The institutional nitrogen footprint calculator is a tool designed for educational and operational purposes at institutions to quantify the impact of their activities on the institution’s N footprint.

The objective of my project is to calculate the nitrogen footprint for Baltimore City, using the calculation to build an urban nitrogen footprint tool with census block groups as the organizational format. The baseline footprint calculation will then be used to test scenarios on what actions could be taken to decrease the N footprint of Baltimore City. The steps to create this tool are establishing system bounds, collecting relevant data, calculating the N footprint, and suggesting reduction strategies. Reduction strategies will include scenarios coinciding with the state of Maryland’s Greenhouse Gas Action Plan as well as some food strategies intended to reduce the N footprint of the area. The intended result of this tool is to be able to communicate and implement N footprint reduction strategies in the Baltimore area by working with stakeholders. The intended users of this tool are scientists, city planners, and other city and county administrators. The model for the Baltimore N footprint calculation model can be applied to other cities in the US to provide an indicator of sustainability across cities.
 
For 2016, the total N footprint of Baltimore City was 17,128 metric tons (MT) N. The per capita N footprint of Baltimore City was 28 kg N. The N footprint of Baltimore is dominated by the food production sector (73%) and is comparable to the US average N footprint on a per capita basis. Energy sectors (electricity use, natural gas use, and transportation) made up 15% of the total Baltimore City N footprint. There is substantial variability among census block groups per capita N footprint within Baltimore City, governed primarily by economic factors. From the findings of this paper, there is a statistically significant relationship between per capita N footprint and per capita annual budgeted expenditures. As an individual’s annual expenditures increase, so does the N footprint for their census block group in Baltimore City. For these census block groups the most effective reductions scenarios are those which decrease the N footprint in the food sector, however these will be the most difficult to implement on a broad scale. The effectiveness and feasibility of food, energy, and transportation scenarios were analyzed and recommendations made for practices to reduce the Baltimore City N footprint.