The League of Conversation Voters launched a $1.9 million TV ad campaign last week targeting Massachusetts Sen. Scott Brown’s (R) environmental record. Today, Brown struck back against the group with an op-ed in the Lowell Sun, the main newspaper of the Bay State’s fourth-largest city.

Defending his environmental record, Brown wrote that the LCV ad “grossly distorts my environmental record.” He went on to outline pieces of pro-environment legislation he had supported and noted that his main priority is getting people back to work.

But Brown also used the op-ed to hammer home a key theme of his campaign’s narrative: He’s an independent Senator.

“I’ve never been part of the inside crowd either on Beacon Hill or on Capitol Hill. I don’t work for any political party, leader or interest group. I work only for the people of Massachusetts,” Brown wrote.

Lowell, a primarily working-class former mill town of about 107,000 people, was the largest city in the state to vote for Brown in the 2010 special election that vaulted him from a little-known state Senator to a national celebrity. Towns and cities like it, with many conservative Democrats, will be a battleground between Brown and Harvard Law School professor Elizabeth Warren, his presumptive Democratic opponent.

Meanwhile, the state Democratic Party is in the midst of an effort to contact thousands of voters and have them call Brown’s office to ask him to vote for the Rebuild America Jobs Act. The effort includes fliers, doorknocking, phonebanking, robocalls, email blasts and social media.

“Call Scott Brown’s office right now and tell him to put politics aside and support President Obama’s plan to get America back to work,” Massachusetts Democratic Party Chairman John Walsh wrote in an email to tens of thousands of supporters around the Bay State.