"photochemical smog" meaning in English

{
  "forms": [
    {
      "form": "photochemical smogs",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "photochemical smog (countable and uncountable, plural photochemical smogs)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "langcode": "en",
          "name": "Photochemistry",
          "orig": "en:Photochemistry",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "air pollution caused by photochemical reactions involving hydrocarbons, nitrogen oxides and other pollutants, especially in still air over cities."
      ],
      "id": "en-photochemical_smog-en-noun-Wgk0Sj9K",
      "links": [
        [
          "air pollution",
          "air pollution"
        ],
        [
          "photochemical reaction",
          "photochemical reaction"
        ],
        [
          "hydrocarbon",
          "hydrocarbon"
        ],
        [
          "nitrogen oxide",
          "nitrogen oxide"
        ],
        [
          "pollutant",
          "pollutant"
        ]
      ],
      "tags": [
        "countable",
        "uncountable"
      ],
      "wikipedia": [
        "photochemical smog"
      ]
    }
  ],
  "word": "photochemical smog"
}

{
  "forms": [
    {
      "form": "photochemical smogs",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "photochemical smog (countable and uncountable, plural photochemical smogs)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English uncountable nouns",
        "en:Photochemistry"
      ],
      "glosses": [
        "air pollution caused by photochemical reactions involving hydrocarbons, nitrogen oxides and other pollutants, especially in still air over cities."
      ],
      "links": [
        [
          "air pollution",
          "air pollution"
        ],
        [
          "photochemical reaction",
          "photochemical reaction"
        ],
        [
          "hydrocarbon",
          "hydrocarbon"
        ],
        [
          "nitrogen oxide",
          "nitrogen oxide"
        ],
        [
          "pollutant",
          "pollutant"
        ]
      ],
      "tags": [
        "countable",
        "uncountable"
      ],
      "wikipedia": [
        "photochemical smog"
      ]
    }
  ],
  "word": "photochemical smog"
}