Emerald Green Arborvitaes, similar to other Arborvitae trees or shrubs, could have foliage turn brown and dry out for a variety of reasons. Not all of them mean your tree is ill or dying, however, so it is important to identify what might be the cause.
Sometimes, your Emerald Green Arborvitae will have some inner branches near the trunk turn brown, and this is simply a natural part of their life cycle. They will experience seasonal needle drop and shed some weight from their inner foliage.
First, check for any bugs or spots in order to rule out pests or fungal infections. Also, make sure to check for root rot by inspecting the roots. If roots are black and sickly, there may not have been enough drainage in the soil and the roots were sitting in water for too long.
If many branches turn brown in the winter, this is likely due to extremely cold temperatures, aggressive cold winds, and not enough water in colder months. This is called winter burn and it is not deadly. While some of these branches may not recover in the spring, typically most do come back - so wait to prune until spring growth is well underway. You can help your arborvitae avoid any winter bronzing by planting them away from harsh and exposed windy areas, wrapping them in burlap for winter protection, and by watering the ground whenever there is a pause in the freezing weather, such as an uncharacteristically warmer day.
If branches have begun to turn brown in the summer months, extreme heat can also be a culprit. Emerald Green Arborvitaes need to stay hydrated, especially during hot summer or droughts. Make sure to provide a deep long watering at least once a week until the drought ends or the weather cools. Mulch can also help keep the temperature around the roots regulated properly.