At Kew, seven miles west of London, the reduction of sunshine due to the London smoke has been placed at 37% for a whole year.
In the United States of America for the decennium, 1901-1910, the aggregate hours of sunshine, percentage of possible sunshine, number of cloudy days, number of partly cloudy days, and number of foggy days have been found by the Pittsburgh smoke investigators, from a study of the records gathered by the United States Weather Bureau in various cities throughout the country, to be as shown in [Table III].
TABLE III.
Statistics of Sunshine in 18 Cities of the United States
| Station. |
1. Aggregate hrs. of sunshine. |
2. Percentage of possible sunshine. |
3. No. of cloudy days. |
4. No. of partly cloudy days. |
5. No. of foggy days. | 6. Total of 3. and 4. |
|---|---|---|---|---|---|---|
| Baltimore | 26,466 | 58.7 | 1440 | 1018 | 142 | 2458 |
| Boston | 25,877 | 56.8 | 1398 | 1003 | 98 | 2401 |
| Buffalo | 23,200 | 49.7 | 1713 | 1324 | 157 | 3037 |
| Chicago | 26,442 | 57.9 | 1238 | 1282 | 116 | 2520 |
| Cincinnati | 26,758 | 58.6 | 1356 | 1202 | 81 | 2588 |
| Cleveland | 22,394 | 47.8 | 1584 | 1187 | 67 | 2771 |
| Denver | 29,355 | 65.9 | 645 | 1500 | 45 | 2145 |
| Detroit | 23,201 | 50.3 | 1477 | 1165 | 133 | 2642 |
| Los Angeles | 31,521 | 70.9 | 743 | 1404 | 258 | 2147 |
| Louisville | 25,715 | 56.8 | 1284 | 1094 | 233 | 2378 |
| New Orleans | 26,091 | 58.6 | 1045 | 1365 | 162 | 2410 |
| New York | 28,762 | 57.6 | 1279 | 1182 | 120 | 2461 |
| Philadelphia | 25,249 | 56.6 | 1369 | 1071 | 127 | 2440 |
| Pittsburgh | 22,573 | 49.0 | 1385 | 1294 | 185 | 2679 |
| Portland, Me. | 26,914 | 59.4 | 1321 | 1040 | 303 | 2361 |
| San Francisco | 25,453 | 56.3 | 900 | 1136 | 241 | 2036 |
| St. Louis | 24,957 | 58.7 | 1185 | 1019 | 42 | 2204 |
| Washington D. C. | 25,078 | 55.8 | 1088 | 1135 | 115 | 2223 |
It is observable that all the cities which have become notorious in the matter of smoke pollution show a very low percentage of sunshine, the worst conditions obtaining in the two cities having the most unsavory reputation for smoke, viz., Cleveland and Pittsburgh. These two cities consistently have the worst records for sunshine, for percentage of possible sunshine and for cloudy and partly cloudy days (combined totals). Unfortunately no meteorological data are available from stations situated in non-smoke-producing centers whose geographical conditions are similar to those obtaining in smoke-producing cities like Pittsburgh, Cleveland, Detroit, Cincinnati and St. Louis. The above data only enable us to compare the atmospheric conditions of one smoky city with another smoky city or with cities whose geographical surroundings are so different as to render the data useless for comparative purposes. However, the data recently collected by the Smoke Investigation of the University of Pittsburgh show, in complete accordance with similar English findings, that the lessened amount of sunshine in Pittsburgh is due to the smoke factor. Figures based on the number of tons of coal consumed in Pittsburgh from 1905 to 1911 show a fair degree of parallelism between the quantity of coal consumed and the number of smoky days. During the years in which an increasing amount of coal has been burned (owing to the heightened cost of gas) the hours of sunshine have fallen from about 2800 to 2200. Likewise the days on which the United States Weather Bureau has observed light or dark smoke in Pittsburgh, have increased as follows for the successive years from 1905-1911: 85, 87, 106, 124, 112, 100 and 156 days (O’Connor, [17]). With the increase of coal consumption has come an increase of smoky days. Dr. Benner tells me that the per cent. of daylight (as chemically determined) in Pittsburgh was reduced for last November about 32%, for December 23%, January 36% and February 44% as compared with the town of Sewickley which is only about 12 miles distant. There can then be no doubt that smoke lessens the amount of sunshine.
Smoke likewise is directly related to the production of moisture, mist, clouds, rain or fogs, because it supplies some of the solid particles which may serve to aid in the formation of suspended drops of water. Rain drops are often formed around a solid nucleus. Without solid particles of dust in the atmosphere there would probably be much less mist, rain and dew ([4]). We would, therefore, infer on merely a priori grounds that smoke contributes to the production of fogs. That this is so seems to be shown by actual investigation. An investigation conducted by the Meteorological Council in 1901-1903 indicated that 20% of the fogs in London were smoke-induced, ([4], [21])—artificially induced and therefore preventable fogs. Most suggestive, as showing that smoke is partly responsible for the existence of fogs, are the fog and smoke statistics gathered in London during the last 30 years, as shown in [Table IV] (applicable to the winter months only). The number of days of fog have been reduced nearly 300% and the hours of bright sunshine have increased nearly 100% during this 30-year period ([10]).
TABLE IV.
| Date | Days of Fog | Hours of bright sunshine |
|---|---|---|
| 1883-1892 | 29.9% | 55.6% |
| 1892-1901 | 20.7% | 70.1% |
| 1901-1910 | 10.6% | 93.5% |
Likewise in Westminster the number of days of fog averaged 27 per year for the lustrum 1902-1906, and 17 per year for the period 1907-1911. The improvement shown above is due, in large part, to the increased use of gas and electricity and to better stoking (Kershaw, Russell). On the other hand, if we turn to Pittsburgh where the amount of smoke has been on the increase in recent years, we find that the number of days of fog increased from an average of 22.6 per year for the first five year period to 50.2 for the second five year period, 1907-1911.