def _to_DOM(self):
        """
        Dumps object data to a fully traversable DOM representation of the
        object.

        :returns: a ``xml.etree.Element`` object

        """
        root_node = ET.Element("no2index")
        reference_time_node = ET.SubElement(root_node, "reference_time")
        reference_time_node.text = str(self._reference_time)
        reception_time_node = ET.SubElement(root_node, "reception_time")
        reception_time_node.text = str(self._reception_time)
        interval_node = ET.SubElement(root_node, "interval")
        interval_node.text = str(self._interval)
        no2_samples_node = ET.SubElement(root_node, "no2_samples")
        for smpl in self._no2_samples:
            s = smpl.copy()
            # turn values to 12 decimal digits-formatted strings
            s['label'] = s['label']
            s['value'] = '{:.12e}'.format(s['value'])
            s['precision'] = '{:.12e}'.format(s['precision'])
            xmlutils.create_DOM_node_from_dict(s, "no2_sample",
                                               no2_samples_node)
        root_node.append(self._location._to_DOM())
        return root_node
Dumps object data to a fully traversable DOM representation of the
        object.

        :returns: a ``xml.etree.Element`` object