@include respond-to(0, $mq-m) {
  .l-article-intro,
  .l-article hr,
  .l-article .related-categories,
  .l-article-main,
  .l-article .related-links {
    @include column(12);
  }
}

@include respond-to($mq-m, $mq-l) {

  .l-article-intro {
    @include column(9);
    @include push(3);
  }

  .l-article .related-categories {
    @include column(3);
  }

  .l-article-main {
    @include column(9);
  }

  .l-article hr {
    @include column(12);
  }

  .l-article .related-links__heading {
    @include column(3);
  }

  .l-article .related-links__category {
    @include column(4);
  }

  .l-article .related-links__category:last-of-type {
    @include column(5);
  }
}

@include respond-to($mq-l) {

  .l-article-intro {
    @include column(7);
    @include push(2);
    @include pull(3);
  }

  .hr--article-intro {
    @include column(9);
  }

  .l-article .related-categories {
    @include column(2);
    clear:left;
  }

  .l-article-main {
    @include column(7);
  }

  .hr--article-related-links {
    display:none;
  }

  .l-article .related-links {
    @include column(3);
    margin-top:-4em;
  }
}

@include respond-to(0, $mq-m) {
  .l-article-intro,
  .l-article hr,
  .l-article .related-categories,
  .l-article-main,
  .l-article .related-links {
    @include column(12);
  }
}

@include respond-to($mq-m, $mq-l) {

  .l-article-intro {
    @include column(9);
    @include push(3);
  }

  .l-article .related-categories {
    @include column(3);
  }

  .l-article-main {
    @include column(9);
  }

  .l-article hr {
    @include column(12);
  }

  .l-article .related-links__heading {
    @include column(3);
  }

  .l-article .related-links__category {
    @include column(9);
    float:right;
  }
}

@include respond-to($mq-l) {

  .l-article-intro {
    @include column(7);
    @include push(2);
    @include pull(3);
  }

  .hr--article-intro {
    @include column(9);
  }

  .l-article .related-categories {
    @include column(2);
    clear:left;
  }

  .l-article-main {
    @include column(7);
  }

  .hr--article-related-links {
    display:none;
  }

  .l-article .related-links {
    @include column(3);
    margin-top:-4em;
  }
}

Change 2 column categories to single columns
Change 2 column categories to single columns
