Gary Guzy will leave his post as deputy director at the end of the month.
EPA chief Gina McCarthy plans to discuss pollution standards with Chinese officials.
The East Coast states want the EPA to place stricter air pollution regulations on Midwest states.
The Supreme Court will hear arguments on the administration's cross-state air pollution rule.
A climate concession could help the Canadian government's case with President Obama.
The agreement allows the Chinese mining company to develop two of the 31 blocks of coal.
The rule would require states cut ozone and fine particle emissions.
More than 90 green groups are asking for more stringent controls on methane emissions.
The withdrawn comments "enabled the false narrative" that hydraulic fracturing is unsafe, Bishop said.
The rule is aimed at preventing collisions between ships and the North Atlantic right whale.