Near Road Air Monitoring Network

On February 9, 2010, U.S. EPA promulgated new minimum monitoring requirements for the NO2 monitoring network in support of newly revised 1-hour NO2 National Ambient Air Quality Standard (NAAQS) and the retained annual NAAQS


On February 9, 2010, U.S. EPA promulgated new minimum monitoring requirements for the NO2 monitoring network in support of newly revised 1-hour NO2 National Ambient Air Quality Standard (NAAQS) and the retained annual NAAQS. To implement the new monitoring requirements, South Coast AQMD is operating near-road NO2 monitoring stations at locations where peak hourly NO2 concentrations are expected to occur within the near-road environment in larger urban areas with consideration to traffic volumes, fleet mix, roadway design, traffic congestion patterns, local terrain or topography, and meteorology in determining where a required near-road NO2 monitor should be placed. Information on how sites were selected was presented at the Near Road Workshop and also the Annual Network Plan Workshop (PDF, 5.3MB).

The current and historical data is available here:

Anaheim Near Road Site

Ontario Near Road Site

Ontario (60 Fwy) Near Road Site

Long Beach (710 Fwy) Near Road Site

It should be noted that an exceedance of the concentration level of a federal standard does not necessarily mean that the NAAQS was violated or that it would cause a nonattainment designation. The 1-hour NO2 NAAQS (100 ppb) is the 3-year average of the annual 98th percentile of the daily maximum 1-hour average concentrations. The annual NO2 NAAQS (53 ppb) is the annual average concentration, averaged over three years.


Use of South Coast AQMD’s Near Road NO2 air quality data is at the user’s discretion and should be done with caution. The intent of the monitoring data is to provide air quality information that is supplemental to the existing South Coast AQMD air quality monitoring regional coverage. This monitor is intended to represent Near Road NO2 concentrations, in which the objective is to determine the air quality impact of NO2 in locations adjacent to the highway source of pollution (motor vehicles). Measurements from this monitor alone cannot determine the relative contributions of regional or source-specific origins to NO2. Local conditions for pollutants can vary widely based on meteorological conditions and proximity to sources of NO2.

This monitor measures Oxides of Nitrogen (NO, NO2, and NOx). NO2 is one of several routinely monitored “criteria” pollutants that the US EPA links to human health impacts, and also is a key ingredient in the production of the secondary criteria pollutant, Ozone (O3). 

Data provided on this website has been reviewed but not yet finalized for EPA submission, and is therefore subject to change. Gaseous analyzers such as this instrument require a daily automated calibration sequence, which disrupts measurements every morning for 1-2 hours. Measurements may also be disrupted for periodic weekly maintenance and quality checks, as well as unforeseen power failures and instrument malfunctions. Data provided is representative only of valid hourly averages, whereby hourly averages with less than 75% valid minute averages were omitted per EPA Quality Assurance guidelines. Finalized data is cross checked against for daily calibration specifications and Quality Assurance Audit thresholds. Until data is finalized for EPA submission, portions of the reviewed quarterly data presented on the South Coast AQMD website may not meet quality assurance criteria, and therefore not be submitted for review of NAAQS attainment.

South Coast AQMD provides no guarantee, either express or implied, as to the accuracy, reliability or completeness of data furnished via the website, maps, or of the forecasts provided in the South Coast AQMD website. Further, South Coast AQMD shall not be liable under any circumstances for any direct, special, incidental or consequential damages with respect to any claim by any user or third party as a result of, or arising from, the use of the data, forecasts or maps.

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