Pollution Levels & ForecastAir Quality Trends & Data  
Welcome to MassAir Online

Download Data Files:
Please select a pollutant:
Please select date period:

Note: This download utility is provided for your convenience and is not the complete final set of validated air monitoring data. If you need a complete and final dataset, please e-mail air.quality@state.ma.us with your data request.

About Downloading Data


How to Get Data
Select a pollutant as well as the year and month for which you wish to download data, then click the button of the format you want. Data are sorted by year and month to ensure faster download times for you and optimum web site performance for other users.


Data Notes (rev April 8, 2009)

Years Available – Data from 2003 - 2006 are currently available for all pollutants and sites. However, note that the 2003-6 data do not contain records for null sample values -- check back with this page to see when the null records are added. More historic data will be added in the near future.

Sample Time – All sample times downloaded from this page are in Easter Standard Time (EST). The maps and graphs display the data in current local time, which is Eastern Daylight Savings Time (EDT) for part of the year.

PM2.5 Data – Note that “Acceptable PM2.5 AQI and Speciation Mass” is the EPA parameter name for fine particulate matter (PM2.5) sampled by 2 different methods. One is the continuous PM monitors that are used for the maps displayed on this site – these data will have no value in the Frequency Code field. The other is for the PM2.5 speciation monitoring program that collects PM2.5 samples for detailed analysis of their chemical components.


Data Types Available

MassDEP air monitoring data from 2007 through yesterday is available for download by month and year. Files are created each night, meaning today’s data will not be available until tomorrow. If you require data for today, click on one or both of these tabs: Trends by Pollutant or Trends by Site.

Note that air monitoring data for certain pollutants – air toxics and lead, for example – require analysis and quality assurance checking after samples are collected. Final data are published on this web site only after this process has been completed.


Data Formats

You may download data in one of three formats, which are described below. There is no difference in the sample values from one format to the other:


Data Quality Review Status

Nearly all of the data available for download from this web page – except for the most recent data from continuous monitors – such as those for fine particles (PM2.5) and ozone (O3) – have undergone quality assurance checks by MassDEP staff. This data has “validated” in the Data Validity Code field in the downloads. Data that has not undergone quality assurance checks by MassDEP will have “raw” in the Data Validity Code field.

Preliminary data from continuous monitors are published here as soon as practical after the end of each hour, but still need to undergo standard quality assurance reviews before being reported as “final” to the U.S. Environmental Protection Agency (EPA). This typically happens within two to three months of the data being collected.

Although preliminary data are generally accurate, a few values occasionally need to be corrected after quality assurance review. Final data are published on this web site when available. Details on review status are provided with any preliminary data you may download.

Learn more about EPA air monitoring quality guidelines.


Understanding the Fields and Codes

Code References – The data uses EPA AQS reference codes in a number of fields. You can find the descriptions for these codes at the EPA AQS Codes and Descriptions web site. For specific tables, the links are given below (these links open .xls files).

Qualifier Codes (XLS file 23KB)
Null Data Codes Old Format (XLS file, 10.5K)
Sample Duration Codes (XLS file, 22K)
Collection Frequency Codes (XLS file, 10K)
Method Codes (by pollutant type – see Protocols with Sampling Methodologies)