Nitrogen References: Scope 3: Food

These food emission factors apply to the 2017, 2018, 2019, and 2020 version of emission factors in SIMAP.

Scope 3: Food      
  Name Unit Source URL Calculations Notes
Food purchases Nitrogen content kg N / kg food USDA Food Composition Database for Standard Reference Average protein content by food category * N content of protein (16%) Average nitrogen content for each food cateogry. Protein contents for the most common products purchased by campuses within each food category were researched from the USDA Food Composition Database. The most common products were identified by reviewing the top 10 purchases by category at multiple campuses. The average protein content of up to 10 relevant products for each category was taken, and that result was multiplied by 16% (protein is 16% nitrogen on average) to determine the average N content of each food category. Please contact us at if you would like to see which products were used for the average protein content calculation. 
Conventional virtual N factor  kg N loss / kg N food Leach et al. 2016, Environmental impact food labels combining carbon, nitrogen, and water footprints. Food Policy 61: 213-223; and Leach et al. 2012, A nitrogen footprint model to help consumers understand their role in nitrogen losses to the environment. Environmental Development 1: 40-66. Updated. Leach et al. 2016:, Leach et al. 2012 : kg N loss / kg N food Virtual nitrogen factors report the total amount of reactive nitrogen released to the enviornment per unit of nitrogen contained in the final product. The factors used in SIMAP are food supply virtual nitrogen factors, meaning that the calculations go through the food supply step of the food production chain. They do not include consumer-level food waste, which is accounted for separately in SIMAP.
Food waste Fraction [FAO] Food and Agriculture Organization of the United Nations  2011. Global food losses and food waste – Extent, causes and prevention. Rome. fraction The food waste factors were collected from Annex 4 of the FAO report for North America by food category. The food percentages used in SIMAP include the last two steps of food production: distribution and consumption. 
Food transport distance mi Hendrickson J. 1994. Energy Use in the U.S. Food System: A Summary of Existing Research and Analysis. mi Average food miles for the US were collected by food category.
Local food transport distance mi AASHE STARS Tehnical Manual Version 2.1, OP 7: Food Purchasing. mi 250 miles was selected because it is a widely used average for local food miles. The AASHE STARS guideline for local and community based from version 2.1 is a 250-mile radius.
Food transport emissions factor kg N / mi US Environmental Protection Agency. 1991. AP-42: Compilation of Air Pollutant Emission Factors, Volume 2: Mobile Sources. (0.00649 kg Nox/mi * 0.3043 kg N/kg Nox) + (0.000257 kg N2O/gal / 5.1 mpg * 0.6364 kg N / kg N2O) = kg N / mi The NOx and N2O emissions factors for a diesel truck were combined into a single emissions factor and converted to units N using the N content of NOx (0.3043) and N2O (0.6364). The calculation for the food transport nitrogen emissions is: Mass food (kg) / truck capacity (kg) * (miles) * (kg N / mi)
Truck capacity kg [USDOT] Comprehensive Truck Size & Weight Study. Rep. U.S. Department of Transportation, 6 Apr. 2011. kg / truck The average capacity of a shipping truck was determined to be approximately 50,000 lb (22,700 kg) from the USDOT database. This figure is used to determine how many trips would be necessary to ship the food items purchased by a campus for the nitrogen transport emissions calculation.