Summary

SECTION 7.11

UNPAVED ROAD DUST — FARM ROADS

(This page last updated on November 19, 2014)

Emission Inventory Source Category
Miscellaneous Processes / Unpaved Road Dust / Unpaved Road Travel Dust

Method Summary: This category includes estimates of fugitive dust particulate matter entrained by vehicular travel on unpaved farm roads. These are typically private roads that are used to access agricultural lands to perform land preparation and harvest operations. This update incorporates current activity data, based on 2005  harvested crop acreage for most of the state, and 2007 farmland acreage for San Joaquin Valley.

Activity Data Source: Annual agricultural unpaved road activity, expressed as pounds PM10 per vehicle mile traveled/acre/year (VMT/acre/year), is based on five crop-specific commodity factors (0.38 - 2.40 VMT/acre/year) and county-specific estimates of either harvested acreage or farmland acreage. Most regions used 2005 harvested acreage from USDA National Agricultural Statistics Services (NASS), as reported by California County Agricultural Commissioners. San Joaquin Valley used 2007 farmland acreage from the California Department of Conservation’s Farmland Mapping and Monitoring Program (FMMP), allocated to the various crops based on NASS harvested acreage reports for 2007. 

Emission Factor Source: The unpaved road dust emission factor (2.0 lbs PM10/VMT) was computed by averaging unpaved road dust emission measurements performed by the University of California, Davis, and the Desert Research Institute. The emissions measurements were performed at sites in the San Joaquin Valley. This emission factor is used for both agricultural and non-agricultural unpaved roads.

Temporal Data: Daily activity on agricultural unpaved roads occurs primarily during daylight hours. Activity is assumed to be the same each day of the week. The monthly activity profile allocates greater emissions to the months having higher agricultural activity levels. 

Changes in Method and Emissions Estimate: This updates incorporates a new method to substantially improve VMT estimates. It replaces the use of a single VMT value for all crops (4.38 VMT/acre/year) with an approach based on crop-specific VMT factors (0.38 - 2.40 VMT/acre/year). The emission factor was reduced by 15%, from 2.27 lbs PM10/VMT to 2.0 lbs PM10/VMT. The emission factor equation uses a revised particle size profile. Activity data were updated and new temporal profiles and growth surrogates were developed. 

Date of Last Update: December 2013

Growth Parameter: Growth in this category is based on projections of harvested crop acreage or farmland acreage and varies by region. 

Statewide Emissions Summary 
(2007 — Annual Average Tons/Day, Uncontrolled)

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