The development There has been an increasing focus on shipping as a contributor to air pollution and regulation with respect to shipping emissions has been on a steady rise over the past decade. The appearance and colour of smoke emitted from ships can be vastly different and ranges from black smoke to invisible smoke. This primarily depends on its composition and source. Black smoke is usually composed of carbon particles (soot), whereas other colored smoke contains water vapour and nitrogen oxide particles among others. Most modern engines produce relatively little smoke at high loads but during transient or low loads such as when starting up or manoeuvring a vessel, a greater quantity of smoke is generated. In an attempt to reduce this form of pollution, a number of countries are amending their legislation and strictly enforcing rules and regulations. Recent changes have taken place in Hong Kong and Dubai. Hong Kong In recent years there has been more focus on air borne pollution in Hong Kong and in an effort to control the emission of dark smoke from vessels, Hong Kong has recently amended its legislation. As per section 50 of the Shipping and Port Control Ordinance (Cap 313) and Section 51 of the Merchant Shipping (Local Vessels) Ordinance (Cap. 548), it is now an offence for any vessel in Hong Kong waters to emit dark smoke for 3 minutes or more continuously at any one time. These legislative changes were gazetted on 18 July 2014 and came into effect immediately. The Shipping and Port Control Ordinance regulates dark smoke emission from ocean-going vessels, whereas the Merchant Shipping (Local Vessels) Ordinance applies to local vessels. Dark smoke is defined as smoke which is "dark as or darker than shade 2 on the Ringelmann chart". The Ringelmann chart has 5 shades ranging from 0 (clear) to 5 (black). The darker the smoke, the more polluting it is. Click on picture to enlarge Sample of the Ringelmann Chart - to be used for reference only, and not as a d