def _quality_check(ds):
    """Check integrity of downloaded dataset. If dataset is invalid,
    `ValueError` is raised.

    :param ds: Dataset to check.
    :type ds: :py:class:`xarray.Dataset`
    """
    if (ds.indexes['time'].year == 1970).any():
        raise ValueError
    for da in ds.values():
        if da.isnull().any() or (da > 10000000000.0).any():
            raise ValueError
